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1.
  1. The site(s) at which P2-receptor agonists act to evoke contractions of the rat isolated tail artery was studied by use of P2-receptor antagonists and the extracellular ATPase inhibitor 6-N,N-diethyl-D-β,γ-dibromomethyleneATP (ARL 67156).
  2. Suramin (1 μM–1 mM) and pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) (0.3–300 μM) inhibited contractions evoked by equi-effective concentrations of α,β-methyleneATP (α,β-meATP) (5 μM), 2-methylthioATP (2-meSATP) (100 μM) and adenosine 5′-triphosphate (ATP) (1 mM) in a concentration-dependent manner. Responses to α,β-meATP and 2-meSATP were abolished, but approximately one third of the peak response to ATP was resistant to suramin and PPADS.
  3. Contractions evoked by uridine 5′-triphosphate (UTP) (1 mM) were slightly inhibited by suramin (100 and 300 μM) and potentiated by PPADS (300 μM).
  4. Desensitization of the P2X1-receptor by α,β-meATP abolished contractions evoked by 2-meSATP (100 μM) and reduced those to ATP (1 mM) and UTP (1 mM) to 15±3% and 68±4% of control.
  5. Responses to α,β-meATP (5 μM) and 2-meSATP (100 μM) were abolished when tissues were bathed in nominally calcium-free solution, while the peak contractions to ATP (1 mM) and UTP (1 mM) were reduced to 24±6% and 61±13%, respectively, of their control response.
  6. ARL 67156 (3–100 μM) potentiated contractions elicited by UTP (1 mM), but inhibited responses to α,β-meATP (5 μM), 2-meSATP (100 μM) and ATP (1 mM) in a concentration-dependent manner.
  7. These results suggest that two populations of P2-receptors are present in the rat tail artery; ligand-gated P2X1-receptors and G-protein-coupled P2Y-receptors.
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2.
  1. The site(s) at which diadenosine 5′,5′′′-P1,P4-tetraphosphate (AP4A) and diadenosine 5′, 5′′′-P1,P5-pentaphosphate (AP5A) act to evoke contraction of the guinea-pig isolated vas deferens was studied by use of a series of P2-receptor antagonists and the ecto-ATPase inhibitor 6-N,N-diethyl-D-β,γ-dibromomethyleneATP (ARL 67156).
  2. Pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) (300 nM–30 μM), suramin (3–100 μM) and pyridoxal-5′-phosphate (P-5-P) (3–1000 μM) inhibited contractions evoked by equi-effective concentrations of AP5A (3 μM), AP4A (30 μM) and α,β-methyleneATP (α,β-meATP) (1 μM), in a concentration-dependent manner and abolished them at the highest concentrations used.
  3. PPADS was more potent than suramin, which in turn was more potent than P-5-P. PPADS inhibited AP5A, AP4A and α,β-meATP with similar IC50 values. No significant difference was found between IC50 values for suramin against α,β-meATP and AP5A or α,β-meATP and AP4A, but suramin was more than 2.5 times more potent against AP4A than AP5A. P-5-P showed the same pattern of antagonism.
  4. Desensitization of the P2X1-receptor by α,β-meATP abolished contractions evoked by AP5A (3 μM) and AP4A (30 μM), but had no effect on those elicited by noradrenaline (100 μM).
  5. ARL 67156 (100 μM) reversibly potentiated contractions evoked by AP4A (30 μM) by 61%, but caused a small, significant decrease in the mean response to AP5A (3 μM).
  6. It is concluded that AP4A and AP5A act at the P2X1-receptor, or a site similar to the P2X1-receptor, to evoke contraction of the guinea-pig isolated vas deferens. Furthermore, the potency of AP4A, but not AP5A, appears to be inhibited by an ecto-enzyme which is sensitive to ARL 67156.
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3.
  1. The effects of NF023, the symmetrical 3′-urea of 8-(benzamido)naphthalene-1,3,5-trisulphonic acid), and its parent compound suramin were investigated on vasoconstrictor responses to α,β-methylene ATP in rabbit isolated saphenous artery and vasodilator responses to ATP in noradrenaline-precontracted rabbit isolated thoracic aorta.
  2. In rabbit isolated saphenous artery, α,β-methylene ATP-induced vasoconstrictor responses via P2X-receptors were concentration-dependently and competitively antagonised by NF023 (30–300 μM; pA2=5.69±0.04). Suramin (100–1000 μM) also competitively blocked vasoconstrictor responses to α,β-methylene ATP, albeit with lower potency (pA2=4.79±0.05). In contrast, NF023 (100 μM) did not significantly affect contractile responses to noradrenaline or histamine in the saphenous artery.
  3. In noradrenaline-precontracted rabbit isolated thoracic aorta preparations, ATP (3–3000 μM) concentration-dependently induced relaxations via endothelium-dependent or smooth muscle P2Y-receptor subtypes. NF023 (30–300 μM) failed to block relaxant responses to ATP at endothelium-dependent P2Y-receptors, whereas suramin (100–1000 μM) did antagonise endothelium-dependent vasodilator responses to ATP. Neither NF023 (100 μM) nor suramin (300 μM) influenced vasorelaxant responses to ATP via endothelium-independent P2Y-receptors.
  4. In conclusion, this study outlines the selectivity of NF023 as an effective P2X-receptor antagonist in rabbit isolated blood vessels without affecting endothelium-dependent or endothelium-independent P2Y-receptor subtypes, adrenoceptors or histamine receptors.
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4.
  1. The electrophysiological actions of several agonists which may differentiate between P2X1- and P2X3-receptors were studied under concentration and voltage-clamp conditions in dissociated neurones of 1–4 day old rat dorsal root ganglia.
  2. β,γ-Methylene-D-ATP (β,γ-me-D-ATP) (1–300 μM), diadenosine 5′,5′′′-P1,P5-pentaphosphate (AP5A) (100 nM–300 μM), diadenosine 5′,5′′′-P1,P4-tetraphosphate (AP4A) (300 nM–300 μM) and uridine 5′-triphosphate (UTP) (1 μM–1 mM) all activated concentration-dependent inward currents with a latency to onset of a few ms.
  3. The concentration-response curves for β,γ-me-D-ATP and AP5A and ATP had similar maximum values, while that for AP4A had a lower maximum. The concentration-response curve to UTP was shallow and did not reach a maximum. β,γ-Methylene-L-ATP was virtually inactive. The rank order of agonist potency was ATP>AP5A≈amp;AP4A>β,γ-me-D-ATP>UTP>>β,γ-methylene-L-ATP.
  4. The inward currents were inhibited by the P2-receptor antagonists suramin (100 μM) and pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) (10 μM). PPADS also inhibited responses to ATP (800 nM) and α,β-methylene ATP (2 μM) in a concentration-dependent manner.
  5. This study shows that β,γ-me-D-ATP, AP5A, AP4A and UTP all act via a suramin- and PPADS-sensitive P2X-receptor to evoke rapid, transient inward currents in dissociated neurones of rat dorsal root ganglia. The very low activity of β,γ-methylene-L-ATP suggests that the agonists were acting at the P2X3-subtype to produce these effects.
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5.
  1. Nucleotide-induced currents in untreated (proliferating) and lipopolysaccharide (LPS; 100 ng ml−1) treated (non-proliferating) rat microglial cells were recorded by the whole-cell patch-clamp technique. Most experiments were carried out on non-proliferating microglial cells. ATP (100 nM–1 mM), ADP (10 nM–10 mM) and UTP (1 μM–100 mM), but not uridine (100 μM–10 mM) produced a slow outward current at a holding potential of 0 mV. The effect of UTP (1 mM) did not depend on the presence of extracellular Mg2+ (1 mM). The outward current response to UTP (1 mM) was similar in non-proliferating and proliferating microglia.
  2. In non-proliferating microglial cells, the ATP (10 μM)-induced outward current was antagonized by suramin (300 μM) or reactive blue 2 (50 μM), whereas 8-(p-sulphophenyl)-theophylline (8-SPT; 100 μM) was inactive. By contrast, the current induced by UTP (1 mM) was increased by suramin (300 μM) and was not altered by reactive blue 2 (50 μM) or 8-SPT (100 μM).
  3. The current response to UTP (1 mM) disappeared when K+ was replaced in the pipette solution by an equimolar concentration of Cs+ (150 mM). However, the effect of UTP (1 mM) did not change when most Cl was replaced with an equimolar concentration of gluconate (145 mM). The application of 4-aminopyridine (1 mM) or Cs+ (1 mM) to the bath solution failed to alter the UTP (1 mM)-induced current. UTP (1 mM) had almost no effect in a nominally Ca2+-free bath medium, or in the presence of charybdotoxin (0.1 μM); the inclusion of U-73122 (5 μM) or heparin (5 mg ml−1) into the pipette solution also blocked the responses to UTP (1 mM). By contrast, the effect of ATP (10 μM) persisted under these conditions.
  4. I-V relations were determined by delivering fast voltage ramps before and during the application of UTP (1 mM). In the presence of extracellular Cs+ (1 mM) and 4-aminopyridine (1 mM) the UTP-evoked current crossed the zero current level near−75 mV. Omission of Ca2+ from the Cs+ (1 mM)- and 4-aminopyridine (1 mM)-containing bath medium or replacement of K+ by Cs+ (150 mM) in the pipette solution abolished the UTP current.
  5. Replacement of GTP (200 μM) by GDP-β-S (200 μM) in the pipette solution abolished the current evoked by UTP (1 mM).
  6. When the pipette solution contained Cs+ (150 mM) instead of K+ and in addition inositol 1,4,5,-trisphosphate (InsP3; 10 μM), an inward current absolutely dependent on extracellular Ca2+ was activated after the establishment of whole-cell recording conditions. This current had a typical delay, a rather slow time course and did not reverse its amplitude up to 100 mV, as measured by fast voltage ramps.
  7. A rise of the internal free Ca2+ concentration from 0.01 to 0.5 μM on excised inside-out membrane patches produced single channel activity with a reversal potential of 0 mV in a symmetrical K+ solution. The reversal potential was shifted to negative values, when the extracellular K+ concentration was decreased from 144 to 32 mM. By contrast, a decrease of the extracellular Cl concentration from 164 to 38 mM did not change the reversal potential.
  8. Purine and pyrimidine nucleotides act at separate receptors in rat microglial cells. Pyrimidinoceptors activate via a G protein the enzyme phospholipase C with the subsequent release of InsP3. The depletion of the intracellular Ca2+ pool appears to initiate a capacitative entry of Ca+ from the extracellular space. This Ca2+ then activates a Ca2+-dependent K+ current.
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6.
  1. The present study was addressed to clarify the subtypes of P2-purinoceptor involved in ATP release and contraction evoked by α,β-methylene ATP (α,β-mATP) and other P2-agonists in guinea-pig ileum.
  2. α,β-mATP 100 μM produced a transient and steep contraction followed by ATP release from tissue segments. These maximum responses appeared with different time-courses and their ED50 values were 5 and 25 μM, respectively. The maximum release of ATP by α,β-mATP was markedly reduced by 250 μM suramin, 30 μM pyridoxal-phosphate-6-azophenyl-2′,5′-disulphonic acid (PPADS) and 30 μM reactive blue 2 (RB-2), P2-receptor antagonists. However, the contractile response was inhibited by suramin, tetrodotoxin and atropine, but not by PPADS and RB-2.
  3. Although the contraction caused by α,β-mATP was strongly diminished by Ca2+-removal and nifedipine, and also by tetrodotoxin and atropine at 0.3 μM, the release of ATP was virtually unaffected by these procedures.
  4. UTP, β,γ-methylene ATP (β,γ-mATP) and ADP at 100 μM elicited a moderate release of ATP. The release caused by UTP was virtually unaffected by RB-2. However, these P2-agonists failed to elicit a contraction of the segment.
  5. The potency order of all the agonists tested for the release of ATP was α,β-mATP>UTP>β,γ-mATP>ADP.
  6. In superfusion experiments with cultured smooth muscle cells from the ileum, α,β-mATP (100 μM) enhanced the release of ATP 5 fold above the basal value. This evoked release was inhibited by RB-2.
  7. These findings suggest that ATP release and contraction induced by P2-agonists such as α,β-mATP in the guinea-pig ileum result mainly from stimulation of different P2-purinoceptors, P2Y-like purinoceptors on the smooth muscles and, probably, P2X-purinoceptors on cholinergic nerve terminals, respectively. However, the ATP release may also be mediated, in part, by P2U-receptors, because UTP caused RB-2-insensitive ATP release.
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7.
  1. This study examined the effects of sodium rhein (0.03–30 μM) on the contractions of the isolated circular muscle of guinea-pig ileum induced by acetylcholine (100 nM), substance P (3 nM) and electrical stimulation (10 Hz for 0.3 s, 100 mA, 0.5 ms pulse duration). The effect of sodium rhein was also evaluated on the ascending excitatory reflex using a partitioned bath (oral and anal compartments). Ascending excitatory enteric nerve pathways were activated by electrical field stimulation (10 Hz for 2 s, 20 mA, 0.5 pulse duration) in the anal compartment and the resulting contraction of the guinea-pig intestinal circular muscle in the oral compartment was recorded.
  2. Sodium rhein (0.3, 3 and 30 μM) significantly potentiated (52±11% at 30 μM) acetylcholine-induced contractions. In the presence of tetrodotoxin (0.6 μM) or ω-conotoxin GVIA (10 nM) sodium rhein (3 and 30 μM) did not enhance, but significantly reduced (49±10% and 44±8%, respectively, at 30 μM) acetylcholine-induced contractions.
  3. Sodium rhein (0.3, 3 and 30 μM) significantly increased (65±11% at 30 μM) substance P-induced contractions. In the presence of tetrodotoxin (0.6 μM), ω-conotoxin GVIA (10 nM) or atropine (0.1 μM), sodium rhein (3 and 30 μM) significantly reduced (50±10%, 55±8% and 46±10%, respectively, at 30 μM) substance P-induced contractions.
  4. NG-nitro-L-arginine methyl ester (L-NAME, 100 μM) abolished the potentiating effect of sodium rhein on acetylcholine and substance P-induced contractions. At the highest concentration (30 μM), sodium rhein, in presence of L-NAME, reduced the acetylcholine (30±6%)- or substance P (36±6%)-induced contractions.
  5. Sodium rhein (30 μM) significantly potentiated (29±9%) the electrically-evoked contractions. L-NAME (100 μM), but not phentolamine, enhanced the effect of sodium rhein. Sodium rhein (30 μM) significantly increased (32±9%) the ascending excitatory reflex when applied in the oral, but not in the anal compartment.
  6. These results indicate that sodium rhein (i) activates excitatory cholinergic nerves on circular smooth muscle presumably through a facilitation of Ca2+ entry through the N-type Ca2+ channel, (ii) has a direct inhibitory effect on circular smooth muscle and (iii) does not affect enteric ascending neuroneural transmission. Nitric oxide could have a modulatory excitatory role on sodium rhein-induced changes of agonist-induced contractions and an inhibitory modulator role on sodium rhein-induced changes of electrically-induced contractions.
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8.
  1. Previous studies have shown that ciprofloxacin and biphenylacetic acid (BPAA) synergistically inhibit γ-aminobutyric acid (GABA)A receptors. In the present study, we have investigated the actions of these two drugs on other neuronal ligand-gated ion channels.
  2. Agonist-evoked depolarizations were recorded from rat vagus and optic nerves in vitro by use of an extracellular recording technique.
  3. GABA (50 μM)-evoked responses, in the vagus nerve in vitro, were inhibited by bicuculline (0.3–10 μM) and picrotoxin (0.3–10 μM), with IC50 values and 95% confidence intervals (CI) of 1.2 μM (1.1–1.4) and 3.6 μM (3.0–4.3), respectively, and were potentiated by sodium pentobarbitone (30 μM) and diazepam (1 μM) to (mean±s.e.mean) 168±18% and 117±4% of control, respectively. 5-Hydroxytryptamine (5-HT; 0.5 μM)-evoked responses were inhibited by MDL 72222 (1 μM) to 10±4% of control; DMPP (10 μM)-evoked responses were inhibited by hexamethonium (100 μM) to 12±5% of control, and αbMeATP (30 μM)-evoked responses were inhibited by PPADS (10 μM) to 21±5% of control. Together, these data are consistent with activation of GABAA, 5-HT3, nicotinic ACh and P2X receptors, respectively.
  4. Ciprofloxacin (10–3000 μM) inhibited GABAA-mediated responses in the vagus nerve with an IC50 (and 95% CI) of 202 μM (148–275). BPAA (1–1000 μM) had little or no effect on the GABAA-mediated response but concentration-dependently potentiated the effects of ciprofloxacin by up to 33,000 times.
  5. Responses mediated by 5-HT3, nicotinic ACh and P2X receptors in the vagus nerve and strychnine-sensitive glycine receptors in the optic nerve were little or unaffected by ciprofloxacin (100 μM), BPAA (100 μM) or the combination of these drugs (both at 100 μM).
  6. GABA (1 mM)-evoked responses in the optic nerve were inhibited by bicuculline with an IC50 of 3.6 μM (2.8–4.5), a value not significantly different from that determined in the vagus nerve. Ciprofloxacin also inhibited the GABA-evoked response with an IC50 of 334 μM (256–437) and BPAA (100 μM) potentiated these antagonist effects. However, the magnitude of the synergy was 48 times less than that seen in the vagus nerve.
  7. These data indicate that ciprofloxacin and BPAA are selective antagonists of GABAA receptors, an action that may contribute to their excitatory effects in vivo. Additionally, our data suggest that the molecular properties of GABAA receptors in different regions of the CNS influence the extent to which these drugs synergistically inhibit the GABAA receptor.
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9.
  1. Inhalation of vanadium compounds, particularly vanadate, is a cause of occupational bronchial asthma. We have now studied the action of vanadate on human isolated bronchus. Vanadate (0.1 μM–3 mM) produced concentration-dependent, well-sustained contraction. Its −logEC50 was 3.74±0.05 (mean±s.e.mean) and its maximal effect was equivalent to 97.5±4.2% of the response to acetylcholine (ACh, 1 mM).
  2. Vanadate (200 μM)-induced contraction of human bronchus was epithelium-independent and was not inhibited by indomethacin (2.8 μM), zileuton (10 μM), a mixture of atropine, mepyramine and phentolamine (each at 1 μM), or by mast cell degranulation with compound 48/80.
  3. Vanadate (200 μM)-induced contraction was unaltered by tissue exposure to verapamil or nifedipine (each 1 μM) or to a Ca2+-free, EGTA (0.1 mM)-containing physiological salt solution (PSS). However, tissue incubation with ryanodine (10 μM) in Ca2+-free, EGTA (0.1 mM)-containing PSS reduced vanadate-induced contraction. A series of vanadate challenges was made in tissues exposed to Ca2+-free EGTA (0.1 mM)-containing PSS with the object of depleting intracellular Ca2+ stores. In such tissues cyclopiazonic acid (CPA; 10 μM) prevented Ca2+-induced recovery of vanadate-induced contraction.
  4. Tissue incubation in K+-rich (80 mM) PSS, K+-free PSS, or PSS containing ouabain (10 μM) did not alter vanadate (200 μM)-induced contraction. Ouabain (10 μM) abolished the K+-induced relaxation of human bronchus bathed in K+-free PSS. This action was not shared by vanadate (200 μM). The tissue content of Na+ was increased and the tissue content of K+ was decreased by ouabain (10 μM). In contrast, vanadate (200 μM) did not alter the tissue content of these ions. Tissue incubation in a Na+-deficient (25 mM) PSS or in PSS containing amiloride (0.1 mM) markedly inhibited the spasmogenic effect of vanadate (200 μM).
  5. Vanadate (200 μM)-induced contractions were markedly reduced by tissue treatment with each of the protein kinase C (PKC) inhibitors H-7 (10 μM), staurosporine (1 μM) and calphostin C (1 μM). Genistein (100 μM), an inhibitor of protein tyrosine kinase, also reduced the response to vanadate.
  6. Vanadate (0.1–3 mM) and ACh (1 μM–3 mM) each increased inositol phosphate accumulation in bronchus. Such responses were unaffected by a Ca2+-free medium either alone or in combination with ryanodine (10 μM).
  7. In human cultured tracheal smooth muscle cells, histamine (100 μM) and vanadate (200 μM) each produced a transient increase in intracellular Ca2+ concentration ([Ca2+]i).
  8. Intracellular microelectrode recording showed that the contractile effect of vanadate (200 μM) in human bronchus was associated with cellular depolarization.
  9. It is concluded that vanadate acts directly on human bronchial smooth muscle, promoting the release of Ca2+ from an intracellular store. The Ca2+ release mechanism involves both the production of inositol phosphate second messengers and inhibition of Ca-ATPase. The activation of PKC plays an important role in mediating vanadate-induced contraction at values of [Ca2+]i that are close to basal.
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10.
  1. Radioligand binding and patch-clamp techniques were used to study the actions of γ-aminobutyric acid (GABA) and the general anaesthetics propofol (2,6-diisopropylphenol), pentobarbitone and 5α-pregnan-3α-ol-20-one on rat α1 and β3 GABAA receptor subunits, expressed either alone or in combination.
  2. Membranes from HEK293 cells after transfection with α1 cDNA did not bind significant levels of [35S]-tert-butyl bicyclophosphorothionate ([35S]-TBPS) (<0.03 pmol mg−1 protein). GABA (100 μM) applied to whole-cells transfected with α1 cDNA and clamped at −60 mV, also failed to activate discernible currents.
  3. The membranes of cells expressing β3 cDNAs bound [35S]-TBPS (∼1 pmol mg−1 protein). However, the binding was not influenced by GABA (10 nM–100 μM). Neither GABA (100 μM) nor picrotoxin (10 μM) affected currents recorded from cells expressing β3 cDNA, suggesting that β3 subunits do not form functional GABAA receptors or spontaneously active ion channels.
  4. GABA (10 nM–100 μM) modulated [35S]-TBPS binding to the membranes of cells transfected with both α1 and β3 cDNAs. GABA (0.1 μM–1 mM) also dose-dependently activated inward currents with an EC50 of 9 μM recorded from cells transfected with α1 and β3 cDNAs, clamped at −60 mV.
  5. Propofol (10 nM–100 μM), pentobarbitone (10 nM–100 μM) and 5α-pregnan-3α-ol-20-one (1 nM–30 μM) modulated [35S]-TBPS binding to the membranes of cells expressing either α1β3 or β3 receptors. Propofol (100 μM), pentobarbitone (1 mM) and 5α-pregnan-3α-ol-20-one (10 μM) also activated currents recorded from cells expressing α1β3 receptors.
  6. Propofol (1 μM–1 mM) and pentobarbitone (1 mM) both activated currents recorded from cells expressing β3 homomers. In contrast, application of 5α-pregnan-3α-ol-20-one (10 μM) failed to activate detectable currents.
  7. Propofol (100 μM)-activated currents recorded from cells expressing either α1β3 or β3 receptors reversed at the C1 equilibrium potential and were inhibited to 34±13% and 39±10% of control, respectively, by picrotoxin (10 μM). 5α-Pregnan-3α-ol-20-one (100 nM) enhanced propofol (100 μM)-evoked currents mediated by α1β3 receptors to 1101±299% of control. In contrast, even at high concentration 5α-pregnan-3α-ol-20-one (10 μM) caused only a modest facilitation (to 128±12% of control) of propofol (100 μM)-evoked currents mediated by β3 homomers.
  8. Propofol (3–100 μM) activated α1β3 and β3 receptors in a concentration-dependent manner. For both receptor combinations, higher concentrations of propofol (300 μM and 1 mM) caused a decline in current amplitude. This inhibition of receptor function reversed rapidly during washout resulting in a ‘surge'' current on cessation of propofol (300 μM and 1 mM) application. Surge currents were also evident following pentobarbitone (1 mM) application to cells expressing either receptor combination. By contrast, this phenomenon was not apparent following applications of 5α-pregnan-3α-ol-20-one (10 μM) to cells expressing α1β3 receptors.
  9. These observations demonstrate that rat β3 subunits form homomeric receptors that are not spontaneously active, are insensitive to GABA and can be activated by some general anaesthetics. Taken together, these data also suggest similar sites on GABAA receptors for propofol and barbiturates, and a separate site for the anaesthetic steroids.
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11.
  1. The influence of L-NG-nitro-arginine (L-NOARG, 30 μM) on contractile responses to exogenous noradrenaline was studied in the rat anococcygeus muscle.
  2. Noradrenaline (0.1–100 μM) contracted the muscle in a concentration-dependent manner. L-NOARG (30 μM) had no effect on noradrenaline responses.
  3. Phenoxybenzamine (Pbz 0.1 μM) depressed by 46% (P<0.001) the maximum response and shifted to the right (P<0.001) the E/[A] curve to noradrenaline (pEC50 control: 6.92±0.09; pEC50 Pbz: 5.30±0.10; n=20).
  4. The nested hyperbolic null method of analysing noradrenaline responses after phenoxybenzamine showed that only 0.61% of the receptors need to be occupied to elicit 50% of the maximum response, indicating a very high functional receptor reserve.
  5. Contractile responses to noradrenaline after partial α1-adrenoceptor alkylation with phenoxybenzamine (0.1 μM) were clearly enhanced by L-NOARG.
  6. The potentiating effect of L-NOARG on noradrenaline responses after phenoxybenzamine was reversed by (100 μM) L-arginine but not by (100 μM) D-arginine.
  7. These results indicate that spontaneous release of NO by nitrergic nerves can influence the α1-adrenoceptor-mediated response to exogenous noradrenaline.
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12.
  1. Nicotine-induced relaxation and release of vasoactive intestinal polypeptide (VIP)- and peptide histidine isoleucine (PHI)-like immunoreactivity (LI) were measured in longitudinal muscle strips from the rat gastric fundus.
  2. Under non-cholinergic conditions (0.3 μM atropine), nicotine (3–300 μM) produced concentration-dependent relaxations of the 5-hydroxytryptamine (3 μM)-precontracted strips. Under non-adrenergic non-cholinergic (NANC) conditions (0.3 μM atropine+1 μM phentolamine+1 μM nadolol), relaxations induced by sub-maximal nicotine concentrations (10 and 30 μM) were significantly smaller, while that produced by the highest concentration used (300 μM) was similar to that seen under non-cholinergic conditions.
  3. Re-exposure to the same nicotine concentration 1 h later induced smaller relaxations, indicating desensitization. The reductions seen in the second responses were proportional to the concentration used.
  4. Under non-cholinergic conditions, the relaxant response to 30 μM nicotine was abolished by hexamethonium (100 μM) and significantly reduced by tetrodotoxin (TTX, 3 μM). The TTX-resistant component was not observed under NANC conditions.
  5. NANC relaxation induced by 30 μM nicotine was significantly reduced by a specific anti-VIP serum (approximately 35% less than that seen with normal rabbit serum).
  6. Nicotine (30–300 μM) caused significant, concentration-dependent increases in the outflow of VIP- and PHI-LI from the strips; these effects were also diminished with re-exposure. The increases in both types of immunoreactivity evoked by nicotine (300 μM) were abolished by hexamethonium (300 μM), TTX (3 μM) and a calcium-free medium.
  7. These findings indicate that VIP and possibly PHI are involved in NANC relaxation of the rat gastric fundus induced by nicotine.
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13.
  1. The effects of nifedipine on both levcromakalim-induced membrane currents and unitary currents in pig proximal urethra were investigated by use of patch-clamp techniques (conventional whole-cell configuration and cell-attached patches).
  2. Nifedipine had a voltage-dependent inhibitory effect on voltage-dependent Ba2+ currents at −50 mV (Ki=30.6 nM).
  3. In current-clamp mode, subsequent application of higher concentrations of nifedipine (⩾30 μM) caused a significant depolarization even after the membrane potential had been hyperpolarized to approximately −82 mV by application of 100 μM levcromakalim.
  4. The 100 μM levcromakalim-induced inward current (symmetrical 140 mM K+ conditions, −50 mV) was inhibited by additional application of three different types of Ca antagonists (nifedipine, verapamil and diltiazem, all at 100 μM). In contrast, Bay K 8644 (1 μM) possessed no activating effect on the amplitude of this glibenclamide-sensitive current.
  5. When 100 μM nifedipine was included in the pipette solution during conventional whole-cell recording at −50 mV, application of levcromakalim (100 μM) caused a significant inward membrane current which was suppressed by 5 μM glibenclamide. On the other hand, inclusion of 5 μM glibenclamide in the pipette solution prevented levcromakalim from inducing an inward membrane current.
  6. The levcromakalim-induced K+ channel openings in cell-attached configuration were suppressed by subsequent application of 5 μM glibenclamide but not of 100 μM nifedipine.
  7. These results suggest that in pig proximal urethra, nifedipine inhibits the glibenclamide-sensitive 43 pS K+ channel activity mainly through extracellular blocking actions on the K+ channel itself.
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14.
  1. We have used whole-cell patch clamping methods to study and characterize the cytolytic P2X7 (P2Z) receptor in the NTW8 mouse microglial cell line.
  2. At room temperature, in an extracellular solution containing 2 mM Ca2+ and 1 mM Mg2+, 2′- and 3′-O-(4-benzoylbenzoyl)-adenosine-5′-triphosphate (Bz-ATP; 300 μM), or ATP (3 mM), evoked peak whole cell inward currents, at a holding potential of −90 mV, of 549±191 and 644±198 pA, respectively. Current-voltage relationships generated with 3 mM ATP reversed at 4.6 mV and did not display strong rectification.
  3. In an extracellular solution containing zero Mg2+ and 500 μM Ca2+ (low divalent solution), brief (0.5 s) application of these agonists elicited larger maximal currents (909±138 and 1818±218 pA, Bz-ATP and ATP, respectively). Longer application of ATP (1 mM for 30 s) produced larger, slowly developing, currents which reached a plateau after approximately 15–20 s and were reversible on washing. Under these conditions, in the presence of ATP, ethidium bromide uptake could be demonstrated. Further applictions of 1 mM ATP produced rapid currents of the same magnitude as those observed during the 30 s application. Subsequent determination of concentration-effect curves to Bz-ATP, ATP and 2-methylthio-ATP yielded EC50 values of 58.3, 298 and 505 μM, respectively. These affects of ATP were antagonized by pyridoxal-phosphate-6-azophenyl- 2′, 4′-disulphonic acid (PPADS; 30 μM) but not suramin (100 μM).
  4. In low divalent solution, repeated application of 1 mM ATP for 1 s produced successively larger currents which reached a plateau, after 8 applications, of 466% of the first application current. PPADS (30 μM) prevented this augmentation, while 5-(N,N-hexamethylene)-amiloride (HMA) (100 μM) accelerated it such that maximal augmentation was observed after only one application of ATP in the presence of HMA. At a bath temperature of 32°C, current augmentation also occurred in normal divalent cation containing solution.
  5. These data demonstrate that mouse microglial NTW8 cells possess a purinoceptor with pharmacological characteristics resembling the P2X7 receptor. We suggest that the current augmentation phenomenon observed reflects formation of the large cytolytic pore characteristic of this receptor. We have demonstrated that pore formation can occur under normal physiological conditions and can be modulated pharmacologically, both positively and negatively.
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15.
  1. Nitric oxide (NO) synthase activity was studied in slices of human temporal cortex samples obtained in neurosurgery by measuring the conversion of L-[3H]-arginine to L-[3H]-citrulline.
  2. Elevation of extracellular K+ to 20, 35 or 60 mM concentration-dependently augmented L-[3H]-citrulline production. The response to 35 mM KCl was abolished by NG-nitro-L-arginine (100 μM) demonstrating NO synthase specific conversion of L-arginine to L-citrulline. Increasing extracellular MgCl2 concentration up to 10 mM also prevented the K+ (35 mM)-induced NO synthase activation, suggesting the absolute requirement of external calcium ions for enzyme activity.
  3. However, the effect of high K+ (35 mM) on citrulline synthesis was insensitive to the antagonists of ionotropic and metabotropic glutamate receptors dizocilpine (MK-801), 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2-3-dione (NBQX) or L-2-amino-3-phosphonopropionic acid (L-AP3) as well as to the nicotinic receptor antagonist, mecamylamine.
  4. The 35 mM K+ response was insensitive to ω-conotoxin GVIA (1 μM) and nifedipine (100 μM), but could be prevented in part by ω-agatoxin IVA (0.1 and 1 μM). The inhibition caused by 0.1 μM ω-agatoxin IVA (∼30%) was enhanced by adding ω-conotoxin GVIA (1 μM) or nifedipine (100 μM). Further inhibition (up to above 70%) could be observed when the three Ca2+ channel blockers were added together. Similarly, synthetic FTX 3.3 arginine polyamine (sFTX) prevented (50% at 100 μM) the K+-evoked NO synthase activation. This effect of sFTX was further enhanced (up to 70%) by adding 1 μM ω-conotoxin GVIA plus 100 μM nifedipine. No further inhibition could be observed upon addition of MK-801 or/and NBQX.
  5. It was concluded that elevation of extracellular [K+] causes NO synthase activation by external Ca+ entering cells mainly through channels of the P/Q-type. Other Ca2+ channels (L- and N-type) appear to contribute when P/Q-channels are blocked.
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16.
  1. The signalling pathway which causes contractions to adenosine 5′-O-2-thiodiphosphate (ADPβS) and α,β-methylene adenosine 5′-diphosphate (α,β-Me ADP) was investigated in rat urinary bladder smooth muscle by measuring isotonic tension.
  2. The responses to 10 μM α,β-methylene adenosine 5′-triphosphate (α,β-Me ATP) in 0 and 3.6 mM Ca2+ were 5.9±1.3 (n=10) and 122.2±6.4 (n=8) % respectively of those obtained in 1.8 mM Ca2+, whereas those to 100 μM ADPβS were 34.6±3.3 (n=8) and 96.8±7.2 (n=8) %, in 0 and 3.6 mM Ca2+, respectively. In both experimental conditions, the responses to the two agonists expressed as % of the control responses were significantly different (P<0.01).
  3. Indomethacin at high concentrations (>1 μM) decreased the responses to α,β-Me ATP (10 μM), ADPβS (100 μM) and α,β-Me ADP (100 μM). However, no significant difference was obtained between the responses to all the agonists at 30 μM indomethacin.
  4. 2-Nitro-4-carboxphenyl n,n-diphenylcarbamate (NCDC) at concentrations between 1 μM and 100 μM concentration-dependently decreased the responses to ADPβS (100 μM) and α,β-Me ADP (100 μM) and almost completely inhibited them at 100 μM. Although the responses to α,β-Me ATP (10 μM) were also inhibited by the drug, at 50 and 100 μM NCDC the responses to α,β-Me ATP were significantly larger than those to ADPβS and α,β-Me ADP (P<0.01).
  5. NCDC 100 μM significantly inhibited the KCl-induced contraction to 65.9±4.9% (n=6) of the control (P<0.01).
  6. It is suggested that the contraction via ADPβS-sensitive receptors in the rat urinary bladder smooth muscle mainly depends on Ca2+ ions liberated from intracellular Ca2+ stores, though the contribution of Ca2+ ions from the extracellular space cannot be neglected. The release of Ca2+ ions from stores is mainly mediated by the production of inositol trisphosphate (IP3) via the activation of phospholipase C.
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17.
  1. The effect of protein tyrosine kinase inhibitors on human adenosine A1 receptor-mediated [3H]-inositol phosphate ([3H]-IP) accumulation has been studied in transfected Chinese hamster ovary cells (CHO-A1) cells.
  2. In agreement with our previous studies the selective adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) stimulated the accumulation of [3H]-IPs in CHO-A1 cells. Pre-treatment with the broad spectrum tyrosine kinase inhibitor genistein (100 μM; 30 min) potentiated the responses elicited by 1 μM (199±17% of control CPA response) and 10 μM CPA (234±15%). Similarly, tyrphostin A47 (100 μM) potentiated the accumulation of [3H]-IPs elicited by 1 μM CPA (280±32%).
  3. Genistein (EC50=13.7±1.2 μM) and tyrphostin A47 (EC50=10.4±3.9 μM) potentiated the [3H]-IP response to 1 μM CPA in a concentration-dependent manner.
  4. Pre-incubation with the inactive analogues of genistein and tyrphostin A47, daidzein (100 μM; 30 min) and tyrphostin A1 (100 μM; 30 min), respectively, had no significant effect on the accumulation of [3H]-IPs elicited by 1 μM CPA.
  5. Genistein (100 μM) had no significant effect on the accumulation of [3H]-IPs produced by the endogenous thrombin receptor (1 u ml−1; 100±10% of control response). In contrast, tyrphostin A47 produced a small augmentation of the thrombin [3H]-IP response (148±13%).
  6. Genistein (100 μM) had no effect on the [3H]-IP response produced by activation of the endogenous Gq-protein coupled CCKA receptor with the sulphated C-terminal octapeptide of cholecystokinin (1 μM CCK-8; 96±6% of control). In contrast, tyrphostin A47 (100 μM) caused a small but significant increase in the response to 1 μM CCK-8 (113±3% of control).
  7. The phosphatidylinositol 3-kinase inhibitor LY 294002 (30 μM) and the MAP kinase kinase inhibitor PD 98059 (50 μM) had no significant effect on the [3H]-IP responses produced by 1 μM CPA and 1 μM CCK-8.
  8. These observations suggest that a tyrosine kinase-dependent pathway may be involved in the regulation of human adenosine A1 receptor mediated [3H]-IP responses in CHO-A1 cells.
  相似文献   

18.
  1. The pharmacological features of the pre- and postsynaptic metabotropic glutamate receptors (mGluRs) present in the guinea-pig olfactory cortex, were examined in brain slices in vitro by use of a conventional intracellular current clamp/voltage clamp recording technique.
  2. Bath-application of trans-aminocyclopentane-1,3-dicarboxylic acid (trans-ACPD) (50 μM) produced a sustained membrane depolarization, increase in cell excitability and induction of a post-stimulus inward (afterdepolarizing) tail current (IADP) (measured under ‘hybrid'' voltage clamp) similar to those evoked by the muscarinic receptor agonist oxotremorine-M (OXO-M, 2 μM).
  3. L-Glutamate (0.25–1 mM, in the presence of 20 μM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 100 μM DL-amino-5-phosphono valeric acid (DL-APV)) or the broad spectrum mGluR agonists 1S,3R-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD, 10 μM), 1S,3S-ACPD (50 μM), ibotenate (Ibo; 25 μM, in the presence of 100 μM DL-APV), the selective mGluR I agonists (S)-3,5-dihydroxyphenylglycine ((S)-3,5-DHPG, 10 μM), (S)-3-hydroxyphenylglycine ((S)-3HPG, 50 μM), or quisqualate (10 μM, in the presence of 20 μM CNQX), but not the mGluR II agonist 2S,1′S,2′S-2-(2′-carboxycyclopropyl)-glycine (L-CCGI, 1 μM) or mGluR III agonist L(+)-2-amino-4-phosphonobutyric acid (L-AP4, 1 mM), were all effective in producing membrane depolarization and inducing a post-stimulus IADP. Unexpectedly, the proposed mGluR II-selective agonist (2S,1′R,2′R,3′R)-2-(2′,3′-dicarboxycyclopropyl)-glycine (DCG-IV, 10 μM, in the presence of 100 μM DL-APV) was also active.
  4. The excitatory effects induced by 10 μM 1S,3R-ACPD were reversibly antagonized by the mGluR I/II antagonist (+)-α-methyl-4-carboxyphenylglycine ((+)-MCPG, 0.5–1 mM), as well as the selective mGluR I antagonists (S)-4-carboxyphenylglycine ((S)-4CPG) and (S)-4-carboxy-3-hydroxyphenyl glycine ((S)-4C3HPG) (both at 1 mM), but not the nonselective mGluR antagonist L(+)-2-amino-3-phosphonopropionic acid (L-AP3, 1 mM) or the selective mGluR III antagonist (S)-α-methyl-L-AP4 (MAP4, 1 mM).
  5. The excitatory postsynaptic potentials (e.p.s.ps), induced by single focal stimulation of cortical excitatory fibre tracts, were markedly reduced by 1S,3R-ACPD or L-AP4 (both at 10 μM), and by the selective mGluR II agonists (mGluR I antagonists) (S)-4CPG or (S)-4C3HPG (both at 1 mM) but not (S)-3,5-DHPG or (S)-3HPG (both at 100 μM).
  6. The inhibitory effects of 1S-3R-ACPD, but not L-AP4, were reversibly blocked by (+)-MCPG (1 mM), whereas those produced by L-AP4, but not 1S,3R-ACPD, were blocked by the selective mGluR III antagonist MAP4 (1 mM).
  7. It is concluded that a group I mGluR is most likely involved in mediating excitatory postsynaptic effects, whereas two distinct mGluRs (e.g. group II and III) might serve as presynaptic inhibitory autoreceptors in the guinea-pig olfactory cortex.
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19.
  1. The effects of the antioxidants ascorbic acid and α-tocopherol and of the metal chelator ethylenediaminetetraacetic acid (EDTA) were studied on relaxations in response to S-nitrosothiols, authentic nitric oxide (NO) and nitrergic non-adrenergic non-cholinergic stimulation of the rat gastric fundus.
  2. The S-nitrosothiols S-nitrosocysteine (1–100 nM), S-nitrosoglutathione (0.01–3 μM) and S-nitroso-N-acetylpenicillamine (0.01–3 μM) induced concentration-dependent relaxations of the rat gastric fundus muscle strips, which were precontracted with prostaglandin F. The relaxations to all S-nitrosothiols were concentration-dependently enhanced by the antioxidants ascorbic acid (0.1–3 μM) and α-tocopherol (3–30 μM) and inhibited by the metal chelator EDTA (26 μM).
  3. Ascorbic acid and α-tocopherol alone did not induce a relaxation of the precontracted rat gastric fundus muscle strip. However, when ascorbic acid (1 μM) or α-tocopherol (1 μM) were injected in the organ bath 1 minute after S-nitrosoglutathione (0.1 μM) or after S-nitroso-N-acetylpenicillamine (0.1 μM), they induced an immediate, sharp and transient relaxation. This relaxation was inhibited by the superoxide generator pyrogallol (2 μM). Such a relaxation to ascorbic acid or α-tocopherol was not observed in the presence of S-nitrosocysteine (10 nM).
  4. Electrical field stimulation (0.5–4 Hz) of the precontracted rat gastric fundus strips induced frequency-dependent nitrergic relaxations which were mimicked by authentic NO (3–300 nM) and by acidified sodium nitrite NaNO2 (0.3–10 μM). Ascorbic acid (0.3–3 μM), α-tocopherol (3–30 μM) or EDTA (26 μM) did not affect the relaxations to nitrergic stimulation, NO or NaNO2.
  5. In summary, relaxations to S-nitrosothiols in the rat gastric fundus are enhanced by the antioxidants ascorbic acid and α-tocopherol and inhibited by the metal chelator EDTA. However, relaxations to nitrergic stimulation of the rat gastric fundus or those to authentic NO were not affected by the antioxidants or by the metal chelator. These results indicate that antioxidants and metal chelators have a different effect on the biological activity of S-nitrosothiols and on that of the nitrergic neurotransmitter. Therefore, our results suggest that S-nitrosothiols do not act as intermediate compounds in nitrergic neurotransmission in the rat gastric fundus.
  相似文献   

20.
  1. 5-Hydroxytryptamine (5-HT; 1 nM–100 μM) concentration-dependently inhibited the amplitude and frequency of spontaneous contractions in longitudinal and circular muscles of the porcine myometrium. The circular muscle (EC50; 68–84 nM) was more sensitive than the longitudinal muscle (EC50; 1.3–1.44 μM) to 5-HT. To characterize the 5-HT receptor subtype responsible for inhibition of myometrial contractility, the effects of 5-HT receptor agonists on spontaneous contractions and of 5-HT receptor antagonists on inhibition by 5-HT were examined in circular muscle preparations.
  2. Pretreatment with tetrodotoxin (1 μM), propranolol (1 μM), atropine (1 μM), guanethidine (10 μM) or L-NAME (100 μM) failed to change the inhibition by 5-HT, indicating that the inhibition was due to a direct action of 5-HT on the smooth muscle cells.
  3. 5-CT, 5-MeOT and 8-OH-DPAT mimicked the inhibitory response of 5-HT, and the rank order of the potency was 5-CT>5-HT>5-MeOT>8-OH-DPAT. On the other hand, oxymethazoline, α-methyl-5-HT, 2-methyl-5-HT, cisapride, BIMU-1, BIMU-8, ergotamine and dihydroergotamine had almost no effect on spontaneous contractions, even at 10–100 μM.
  4. Inhibition by 5-HT was not decreased by either pindolol (1 μM), ketanserin (1 μM), tropisetron (10 μM), MDL72222 (1 μM) or GR113808 (10 μM), but was antagonized by the following compounds in a competitive manner (with pA2 values in parentheses): methiothepin (8.05), methysergide (7.92), metergoline (7.4), mianserin (7.08), clozapine (7.06) and spiperone (6.86).
  5. Ro 20-1724 (20 μM) and rolipram (10 μM) significantly enhanced the inhibitory response of 5-HT, but neither zaprinast (10 μM) nor dipyridamole (10 μM) altered the response of 5-HT.
  6. 5-HT (1 nM–1 μM) caused a concentration-dependent accumulation of intracellular cyclic AMP in the circular muscle.
  7. From the present results, the 5-HT receptor, which is functionally correlated with the 5-HT7 receptor, mediates the inhibitory effect of 5-HT on porcine myometrial contractility. This inhibitory response is probably due to an increase in intracellular cyclic AMP through the activation of adenylate cyclase that is positively coupled to 5-HT7 receptors.
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