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1.
The release of 3H-(-)-noradrenaline (NA) from rat vas deferens in vitro was examined under various experimental conditions. It was found that in normal and reserpinized vas deferens the release of NA evoked by (+)-amphetamine (5 X 10(-6) M) or low external Na+ (26 mM) was antagonized by imipramine methiodide and desipramine, inhibitors of the NA uptake, but was not dependent on the presence of Ca2+ in the medium and was not antagonized by the potent local anaesthetic agent bethoxycaine. The release evoked by veratridine in reserpinized tissue was antagonized by the uptake inhibitors but was in normal tissue only partially inhibited in presence of Ca2+ but almost completely in absence of Ca2+. The release by high K+ (117 mM)+low Na+ (26 mM) in normal tissue was dependent on the presence of Ca2+ and was antagonized by the muscarinic agonists carbacholine and metacholine and by high concentrations of desipramine. In the reserpinized vasa the corresponding release was not dependent on Ca2+ and was not antagonized by the muscarinic agents but was inhibited by high concentrations of desipramine. 相似文献
2.
High spatial resolution studies of muscarinic neuroeffector junctions in mouse isolated vas deferens
It is acknowledged that neurotransmission in the mouse vas deferens is predominantly mediated by ATP and noradrenaline (NA) released from sympathetic nerves while cholinergic transmission in the rodent vas deferens is often overlooked despite early literature. Recently we have characterized a cholinergic component of neurogenic contraction of mouse isolated vas deferens. In the present paper, by confocal imaging of Ca2+ dynamics we detected acetylcholine (ACh) action at muscarinic cholinergic neuroeffector junctions at high-resolution. Experiments were carried out in the presence of prazosin (100 nM) and α,β methylene ATP (α,β-MeATP) (1 μM) to inhibit responses to NA and ATP respectively. Exogenous ACh (10 μM) elicited Ca2+ transients, an effect blocked by the muscarinic receptor antagonist, cyclopentolate (1 μM). Ca2+ transients were evoked by electrical stimulation of intrinsic nerves in the presence of the cholinesterase inhibitor neostigmine (10 μM). Stimulation produced a marked increase in the frequency and number of Ca2+ transients. Cyclopentolate reduced the frequency of occurrence of spontaneous and evoked events to control levels. The α2-adrenoceptor antagonist yohimbine (300 nM) did not affect the spontaneous Ca2+ transients, but increased the frequency of occurrence of evoked transients, an effect inhibited by cyclopentolate. The postjunctional effects of neuronally-released ACh are limited by the action of cholinesterase. Release of ACh appears to be tonically inhibited by NA released from sympathetic nerve terminals through action at prejunctional α2-adrenoceptors. Tetrodotoxin (TTX, 300 nM) abolished the nerve-evoked Ca2+ events, with no effect on Ca2+ transients elicited by exogenous ACh. In conclusion, the presence of spontaneous and evoked cholinergic Ca2+ transients in smooth muscle cells of the mouse isolated vas deferens has been revealed. These events are mediated by ACh acting at M3 muscarinic receptors. This action stands in marked contrast to the lack of effect of neuronally-released NA on smooth muscle Ca2+ dynamics in this tissue. 相似文献
3.
M. M. Vohra 《Inflammation research》1979,9(4):319-326
The effect of histamine on adrenergic neurotransmission in the mouse isolated vas deferens preparation was investigated. Concentrations of histamine ranging from 0.2 to 650 M depressed, in a dose-related manner, not only the contractile response elicited by field stimulation but also the response caused by the addition of exogenous noradrenaline and acetylcholine. However, the release of [3H]-NA evoked by field stimulation or by high K+ remained unchanged in the presence of these concentrations of histamine. The inhibitory effect of histamine on the contractile responses caused by various stimuli was reduced or completely antagonized by cimetidine, a histamine H2-receptor antagonist but not by mepyramine, a conventional antihistamine. The inhibitory effect of histamine was found to be inversely proportional to both the Ca2+ concentration in the bathing medium and to the frequency of field stimulation. Further, the inhibitory effect of histamine was markedly reduced when Mg2+ was omitted from the bathing medium. It is concluded that the mouse vas deferens preparation contains a post-junctional inhibitory H2-receptor. The stimulation of H2-receptors by histamine inhibits the contractile response of the vas deferens, possibly by decreasing the availability of Ca2+ required for contraction by depressing the influx of Ca2+. 相似文献
4.
Cell-free, Ca2+ dependent phospholipase A2 activity (PLA2) was measured in human synovial fluid of patients with various kinds of arthritis using [1–14C] oleate-labelled autoclaved Escherichia coli as substrate. PLA2 activity at pH 7.0 and with 5 mM added Ca2+ was stimulated and then inhibited in a dose-dependent fashion by NaCl; maximal stimulation of 8.8 fold was found at 150 mM Na+. Similar effects were obtained with K+ Li+ and Ru+. In the absence of added Na+, PLA2 activity was maximal with 25 mM Ca2+ (145 nmols/hr/mg), but in the presence of 150 mM Na+, activity was maximal with 4 mM Ca2+ (415 nmols/hr/mg). PLA2 activity was optimal between pH 6.5–8.0 in presence of 150 mM Na+1 and 4 mM Ca2+. There was no significant difference between PLA2 activity in synovial fluids from rhematoid and other types of arthritis. Neutral active, Ca2+-dependent PLA2 activity in acid extracts of human platelets, plasma, polymorphonuclear leukocytes and synovial fluid varied in response to added Na+. In presence of 150 mM added Na+ and 5 mM PLA2 activity in human synovial fluid was inhibited by all multivalent cations tested. In the absence of Na+, Cu2+ and Mg2+ stimulated PLA2 activity in a dose dependent fashion; whereas, Fe2+, Fe3+ and Al3+ were inhibitory. The extent of stimulation by Mg2+ was inversely related to the concentration of added Ca2+. 相似文献
5.
Bernd Engelmann Volkmar Gross Udo Schumacher Jochen Duhm 《Pflügers Archiv : European journal of physiology》1992,421(5):497-502
To examine the functional significance of epidermal growth factor (EGF) binding sites present on the human erythrocyte membrane [Engelmann et al. (1992) Am J Hematol 39:239–241], the effect of EGF on 45Ca2+ uptake and on 22Na+ efflux from these cells has been studied. In all cases media contained 1.25 mM Ca2+, whereas Na+ and K+ were varied. In 140 mM Na+/5 mM K+ medium EGF (250 ng/ml) stimulated 45Ca2+ uptake by 50%–90% in quin-2-loaded cells, and by up to threefold in untreated cells. Increasing extracellular K+ up to 75 mM at the expense of extracellular Na2+ stimulated the EGF-induced 45Ca2+ uptake by about twofold compared to 145 mM Na+ medium both in quin-2-loaded and in untreated cells. In 145 mM K+ medium, however, no EGF-induced 45Ca2+ uptake was detectable in quin-2-loaded cells, while in untreated cells Ca2+ entry was stimulated twofold by EGF. After increasing intracellular Na+ from 6 mmol/l cells to 18 mmol/l cells in untreated cells suspended in 145 mM K+ medium, 45Ca2+ uptake induced by EGF gradually increased. In contrast, in 140 mM Na+/5 mM K+ as well as in 70 mM Na+/75 mM K+ medium, 45Ca2+ uptake accelerated by EGF was largely unaffected by a modified red cell Na+ content. When 22Na-loaded untreated red cells were suspended in 145 mM K+ medium EGF stimulated red cell 22Na+ efflux by more than threefold. In 140 mM Na+/5 mM K+ as well as in 70 mM Na+/75 mM K+ medium, no 22Na+ efflux induced by the growth factor was evident. The results are consistent with the idea that EGF stimulates (at least) two components of 45Ca2+ uptake in human erythrocytes. One of the two is unmasked in 145 mM K+ medium, inhibited by quin-2 loading, accelerated by intracellular Na+ and appears to involve reversed Na+/Ca2+ exchange. 相似文献
6.
M. A. Jansen C. J. A. Van Echteld T. J. C. Ruigrok 《Pflügers Archiv : European journal of physiology》1998,436(4):515-520
Ca2+ paradox damage has been suggested to be determined by Na+ entry during Ca2+ depletion and exchange of Na+ for Ca2+ during Ca2+ repletion. Since previously a Ca2+ paradox without prior increase of total intracellular [Na+] ([Na+]i) has been observed, we investigated whether local accumulation of Na+ close to the inner side of the sarcolemma during Ca2+ depletion plays a role in the Ca2+ paradox by replacing all extracellular Na+ by Li+ 5 min before and during 10 min Ca2+-free perfusion (37°C) in isolated rat hearts (group I). Subsequently, hearts were perfused with a standard, Na+- and Ca2+-containing solution. Verapamil was used to prevent contracture due to the absence of Na+/Ca2+ exchange during Na+-free perfusion in the presence of Ca2+. In group II, the Ca2+-free period was omitted, and in group III normal extracellular [Na+] was used throughout. 23Na-NMR was used to monitor intra- and extracellular Na+ signals. Total creatine kinase release was 2,977±413, 36±24 and 3170±297 IU/g dry weight in groups I, II and III respectively,
indicating a full Ca2+ paradox in groups I and III. [Na+]i decreased from 11.3±0.6 mM during control perfusion to 1.2±0.4 mM after 10 min Ca2+ depletion in group I, whereas in group III [Na+]i was 10.9±2.2 mM during control perfusion and did not change significantly after 10 min Ca2+-free perfusion. It is concluded that accumulation of Na+ close to the inner side of the sarcolemma during Ca2+ depletion is not a prerequisite for the Ca2+ paradox.
Received: 2 February 1998 / Received after revision: 31 March 1998 / Accepted: 9 April 1998 相似文献
7.
Bo Hellman Janove Sehlin Inge-Bert Täljedal 《Pflügers Archiv : European journal of physiology》1978,378(2):93-97
Microdissected pancreatic islets of noninbredob/ob-mice were used to study ionic effects on the lanthanum-nondisplaceable45Ca2+ uptake by islet cells. Omission of Mg2+ from the incubation medium had no effect, but the45Ca2+ uptake was increased by omission of Na+ and decreased by omission of K+. Excess Mg2+ (1.2–15 mM) inhibited and excess K+ (4.7–25 mM) stimulated the45Ca2+ uptake in a concentration-dependent manner. Stimulation of45Ca2+ uptake in Na+-deficient islets was associated with an enhancement of the basal insulin release. Total abolishment of glucose-stimulated45Ca2+ uptake in K+-deficient islets did not preclude a significant secretory response to glucose. It is concluded that the lanthanum-nondisplaceable45Ca2+ uptake shows a partial correlation to insulin release. 相似文献
8.
Yamazaki T Akiyama T Kitagawa H Komaki F Mori H Kawada T Sunagawa K Sugimachi M 《Acta physiologica (Oxford, England)》2007,191(4):275-284
Aim: Although ouabain modulates autonomic nerve ending function, it is uncertain whether ouabain‐induced releasing mechanism differs between in vivo sympathetic and parasympathetic nerve endings. Using cardiac dialysis, we examined how ouabain induces neurotransmitter release from autonomic nerve ending. Methods: Dialysis probe was implanted in left ventricle, and dialysate noradrenaline (NA) or acetylcholine (ACh) levels in the anaesthetized cats were measured as indices of neurotransmitter release from post‐ganglionic autonomic nerve endings. Results: Locally applied ouabain (100 μm ) increased in dialysate NA or ACh levels. The ouabain‐induced increases in NA levels remained unaffected by cardiac sympathetic denervation and tetrodotoxin (Na+ channel blocker, TTX), but the ouabain‐induced increases in ACh levels were attenuated by TTX. The ouabain‐induced increases in NA levels were suppressed by pretreatment with desipramine (NA transport blocker) and augmented by reserpine (vesicle NA transport blocker). In contrast, the ouabain‐induced increases in ACh levels remained unaffected by pretreatment with hemicholinium‐3 (choline transport blocker) but suppressed by vesamicol (vesicle ACh transport blocker). The ouabain‐induced increases in NA levels were suppressed by pretreatment with ω‐conotoxin GVIA (N‐type Ca2+ channel blocker), verapamil (L‐type Ca2+ channel blocker) and TMB‐8 (intracellular Ca2+ antagonist). The ouabain‐induced increases in ACh levels were suppressed by pretreatment with ω‐conotoxin MVIIC (P/Q‐type Ca2+ channel blocker), and TMB‐8. Conclusions: Ouabain‐induced NA release is attributable to the mechanisms of regional exocytosis and/or carrier‐mediated outward transport of NA, from stored NA vesicle and/or axoplasma, respectively, while the ouabain‐induced ACh release is attributable to the mechanism of exocytosis, which is triggered by regional depolarization. At both sympathetic and parasympathetic nerve endings, the regional exocytosis is because of opening of calcium channels and intracellular calcium mobilization. 相似文献
9.
Carlos B. Duarte Ildete L. Ferreira Arsélio P. Carvalho Caetana M. Carvalho 《Pflügers Archiv : European journal of physiology》1993,423(3-4):314-323
The specific inhibitor of the -aminobutyric acid (GABA) carrier, NNC-711, {1-[(2-diphenylmethylene) amino]oxyethyl}-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride, blocks the Ca2+-independent release of [3H]GABA from rat brain synaptosomes induced by 50 mM K+ depolarization. Thus, in the presence of this inhibitor, it was possible to study the Ca2+-dependent release of [3H]GABA in the total absence of carrier-mediated release. Reversal of the Na+/Ca2+ exchanger was used to increase the intracellular free Ca2+ concentration ([Ca2+]i) to test whether an increase in [Ca2+]i alone is sufficient to induce exocytosis in the absence of depolarization. We found that the [Ca2+]i may rise to values above 400 nM, as a result of Na+/Ca2+ exchange, without inducing release of [3H]GABA, but subsequent K+ depolarization immediately induced [3H]GABA release. Thus, a rise of only a few nanomolar Ca2+ in the cytoplasm induced by 50 mM K+ depolarization, after loading the synaptosomes with Ca2+ by Na+/Ca2+ exchange, induced exocytotic [3H]GABA release, whereas the rise in cytoplasmic [Ca2+] caused by reversal of the Na+/Ca2+ exchanger was insufficient to induce exocytosis, although the value for [Ca2+]i attained was higher than that required for exocytosis induced by K+ depolarization. The voltage-dependent Ca2+ entry due to K+ depolarization, after maximal Ca2+ loading of the synaptosomes by Na+/Ca2+ exchange, and the consequent [3H]GABA release could be blocked by 50 M verapamil. Although preloading the synaptosomes with Ca2+ by Na+/Ca2+ exchange did not cause [3H]GABA release under any conditions studied, the rise in cytoplasmic [Ca2+] due to Na+/Ca2+ exchange increased the sensitivity to external Ca2+ of the exocytotic release of [3H]GABA induced by subsequent K+ depolarization. Thus, our results show that the vesicular release of [3H]GABA is rather insensitive to bulk cytoplasmic [Ca2+] and are compatible with the view that GABA exocytosis is triggered very effectively by Ca2+ entry through Ca2+ channels near the active zones. 相似文献
10.
Noriyoshi Teramoto Hai-Lei Zhu Mari Yotsu-Yamashita Tetsuichiro Inai Thomas C. Cunnane 《Pflügers Archiv : European journal of physiology》2012,464(5):493-502
Patch-clamp experiments were performed to investigate the molecular properties of resurgent-like currents in single smooth muscle cells dispersed from mouse vas deferens, utilizing both NaV1.6-null mice (NaV1.6?/?), lacking the expression of the Scn8a Na+ channel gene, and their wild-type littermates (NaV1.6+/+). NaV1.6 immunoreactivity was clearly visible in dispersed smooth muscle cells obtained from NaV1.6+/+, but not NaV1.6?/?, vas deferens. Following a depolarization to +30?mV from a holding potential of ?70?mV (to produce maximal inactivation of the Na+ current), repolarization to voltages between ?60 and +20?mV elicited a tetrodotoxin (TTX)-sensitive inward current in NaV1.6+/+, but not NaV1.6?/?, vas deferens myocytes. The resurgent-like current in NaV1.6+/+ vas deferens myocytes peaked at approximately ?20?mV in the current–voltage relationship. The peak amplitude of the resurgent-like current remained at a constant level when the membrane potential was repolarized to ?20?mV following the application of depolarizing rectangular pulses to more positive potentials than +20?mV. 4,9-Anhydrotetrodotoxin (4,9-anhydroTTX), a selective NaV1.6 blocking toxin, purified from a crude mixture of TTX analogues by LC-FLD techniques, reversibly suppressed the resurgent-like currents. β-Pompilidotoxin, a voltage-gated Na+ channel activator, evoked sustained resurgent-like currents in NaV1.6+/+ but not NaV1.6?/? murine vas deferens myocytes. These results strongly indicate that, primarily, resurgent-like currents are generated as a result of NaV1.6 channel activity. 相似文献
11.
The regulation of blood vessel diameter is under the control of the autonomic nervous system (as well as hormones and metabolites), sympathetic nerve stimulation evoking depolarizing post-synaptic potentials. Excitatory junction potentials (EJPs) were recorded from vascular smooth muscle cells of guinea-pig small mesenteric arteries (pressurized) following nerve stimulation. Repetitive stimulation (>5Hz) led to summation of EJPs, which evoked spikes and vasoconstriction. Replacing extracellular Na+ with choline (plus atropine) resulted in a decrease in EJP amplitude, but spike amplitude and maximum rate of rise (+Vmax) were unaffected. Decreasing the extracellular Ca2+ concentration produced decreases in EJP amplitude and spike +Vmax, while increasing extracellular Ca2+ resulted in increased EJP amplitude and spike +Vmax. Verapamil and bepridil, agents that depress Ca2+ influx in vascular and visceral smooth muscle, depolarized the membrane and depressed EJPs and spikes at high concentrations (10–5 M and 5×10–6 M, respectively). The data indicate that EJPs are dependent on external Na+ and Ca2+ ions, and that spikes are dependent on Ca2+. Thus, neuromuscular transmission in this muscle is similar to that in non-vascular smooth muscles, such as intestinal muscle and vas deferens.Part of this work has been presented to the Biophysical Society (Zelcer and Sperelakis 1980) and to the American Physiological Society (Zelcer and Sperelakis 1981) 相似文献
12.
Peter E. Jensen Michael J. Mulvany Christian Aalkjaer 《Pflügers Archiv : European journal of physiology》1992,420(5-6):536-543
The relationship between isometric tension and free cytoplasmic calcium, [Ca2+]i, was investigated in rat isolated resistance arteries using fura-2. Depolarisation with 125 mM K+ induced a tonic contraction, while [Ca2+]i increased transiently but stabilised above resting [Ca2+]i. Furthermore, the tension/[Ca2+]i ratio was lower during activation with 125 mM K+ if the effect of endogenous noradrenaline (NA) was inhibited. Concentration/ response curves with NA and K+ indicated that NA increased the sensitivity to [Ca2+]i. Calcium concentration/response curves in the presence of 10 M NA or 125 mM K+ showed that NA could induce force at or below resting [Ca2+]i, while for any given bath calcium concentration, [Ca2+]i was similar in the presence of NA or K+. Addition of NA or vasopressin (AVP) to vessels depolarised with 125 mM K+ caused force development but no increase in [Ca2+]i, suggesting that agonists increase the efficacy of [Ca2+]i. However, during activation with AVP the efficacy of [Ca2+]i decreased time-dependently. The results suggest that in resistance arteries [Ca2+]i plays a crucial role in excitation-contraction coupling, but the tension/[Ca2+]i relationship can be modified by exogenous and endogenous agonists. 相似文献
13.
A. TEDESCHI M. ARQUATI M. PALELLA N. MILAZZO A. MIADONNA 《Clinical and experimental allergy》1994,24(1):66-72
The effects of different extracellular Na+ and CV2+ concentrations on histamine release from human basophils were investigated. Isosmotic replacement of extracellular Na + either with choline +, a non-permeant Na + analogue, or glucose significantly increased spontaneous and anti-IgE-induced histamine release. Basophils from 12 of 49 normal subjects, which were found not to release histamine upon challenge with an optimal dose of anti-IgE in a 135 mM NaCl buffer, were converted into releasing basophils when stimulation with anti-IgE was performed in a low-Na+ medium. The increase in Na + concentration in the extracellular medium was accompanied by a reduction in the magnitude of basophil response to anti-IgE, which was significantly more pronounced in non-releasers than in releasers (per cent inhibition by 70 mM NaCl 75.5 + 3.2 vs 43.5 + 9.0, P < 0.01). At higher Na+ concentrations a progressive and almost complete abrogation of histamine release was observed in non-releasers, but not in releasers (maximal per cent inhibition at 140 mM NaCl 97.3+1.3 vs 50.4 + 8.6). The Na+/H+ exchanger monensin had a dose-dependent inhibitory effect on anti-IgE-induced histamine release, and the concentration inhibiting 50% of histamine release was l.5 × 10?7M. When basophils were challenged in the presence of different Na+ and C2+ concentrations, it was shown that the two cations have antagonistic effects, which is to say that they down-regulate and upregulate histamine release, respectively. Moreover, the requirement of extracellular Ca2+ was lowered in a low-Na+ medium. These results suggest that Na+ and Ca+ ions contribute with opposite effects to the modulation of basophil response to anti-IgE and that non-releasing basophils are converted into releasing basophils in a low-Na + medium. 相似文献
14.
Uehara A. Iwamoto T. Shigekawa M. Imanaga I. 《Pflügers Archiv : European journal of physiology》1997,434(3):335-338
A conventional patch-clamp technique was used to record the whole-cell current from the cloned canine cardiac Na+/Ca2+ exchanger NCX1 overexpressed in a fibroblast cell. Ca2+ was extracellularly applied to the Na+-loaded cell to activate the outward current by operating the reverse mode of NCX1. No measurable outward current was ever
elicited from the nontransfected cell. Na+/Ca2+ exchange blocker 5 mM Ni2+ or 3 μM KB-R7943 that was applied extracellularly abolished the outward current. With 140 mM external Li+ (replacing Na+), the outward current was transient during the Ca2+ application. In contrast, with 140 mM external Na+, the outward current was maintained without any inactivation during the Ca2+ application. I–V relations predicted from the whole-cell clamp protocols used were obtained both before and during the Ca2+ application. The exchanger whole-cell currents are thus successfully detectable from NCX1 which is overexpressed in this stable
transfectant system.
Received: 28 February 1997 / Accepted: 9 April 1997 相似文献
15.
R. J. M. Bindels P. L. M. Ramakers J. A. Dempster A. Hartog C. H. van Os 《Pflügers Archiv : European journal of physiology》1992,420(5-6):566-572
Cells from connecting tubule and cortical collecting duct of rabbit kidney were isolated by immunodissection with mAb R2G9 and cultured on permeable filters. Confluent monolayers developed an amiloride-sensitive transepithelial potential difference of –50±1 mV (lumen negative) and a transepithelial resistance of 507±18 cm2. Transepithelial Ca2+ transport increased dose-dependently with apical [Ca2+] and, in solutions containing 1 mM Ca2+, the active transcellular Ca2+ transport rate was 92±2 nmol h–1 cm–2. Transcellular Ca2+ transport was dependent on basolateral Na+ (Na
b
+
). Isoosmotic substitution of Na
b
+
for N-methylglucamine resulted in a concentration-dependent decrease in Ca2+ absorption, with maximal inhibition of 67±5%. A Hill plot of the Na+-dependence yielded a coefficient of 1.9±0.4, indicating more than one Na+ site on a Na+-dependent Ca2+ transport system. In addition, the absence of Ca
b
2+
resulted in a significant increase in Ca2+ transport both in the presence and absence of Na
b
+
. Added basolaterally, ouabain (0.1 mM) inhibited Ca2+ transport to the same extent as did Na+-free solutions, while bepridil (0.1 mM), an inhibitor of Na+/Ca2+ exchange, reduced Ca2+ transport by 32±6%. Methoxyverapamil, felodipine, flunarizine and diltiazem (10 M) were without effect. Depolarisation of the basolateral membrane, by raising [K+]b to 60 mM, significantly decreased transcellular Ca2+ transport, which is indicative of electrogenic Na+/Ca2+ exchange. In conclusion, active Ca2+ transport in the collecting system of rabbit kidney is largely driven by basolateral Na+/Ca2+ exchange. However, a residual Ca2+ absorption of about 30% was always observed, suggesting that other Ca2+ transport mechanisms, presumably a Ca2+-ATPase, participate as well. 相似文献
16.
An analysis of the mechanisms underlying the non-quantal release of acetylcholine at the mouse neuromuscular junction 总被引:6,自引:0,他引:6
The hyperpolarization produced by the application of 10?5 M d-tubocurarine to the end-plate of mouse diaphragm-phrenic nerve preparation pretreated with an irreversible anticholinesterase was studied. This hyperpolarization has been attributed to a non-quantal release of acetylcholine by the nerve terminals. The usual hyperpolarization effect of about 10 mV was mimicked by adding 10?7 M acetylcholine to the bath which contained 15mM Ca2+ to block the non-quantal release. The hyperpolarization effect was maximal (9.2 ± 0.8mV) in saline solution with the normal concentrations of Ca2+ (2mM) and K+ (5mM). Reducing [Ca2+] in the bath decreased the hyperpolarization effect. In Ca-free solution with 4.10?4 M ethleneglycoltetra-acetate the hyperpolarization effect was3.8 ± 0.6mV. An increase of [Ca2+] also reduced the hyperpolarization effect and it was absent in 15mM of Ca2+. When the external concentration of Ca2+ was kept constant (2mM), both decreasing and increasing K+ concentration from 5 mM diminished the hyperpolarization effect. However, the decrease at elevated K+ concentrations was due to a reduction of membrane resistance and when the hyperpolarization effect was corrected for the change in size of the miniature endplate potential, it was unchanged in solutions with increased [K+] up to 13 mM. No traces of non-quantal release were observed during repetitive stimulation of the phrenic nerve in a medium containing 0.3 mM Ca2+. The hyperpolarization effect was not found in denervated muscles that lacked signs of neuromuscular transmission. The hyperpolarization effect was blocked by botulinum toxin while some evoked release of ACh was present. The time required for the block by 1 μg/ml toxin was shorter than for 0.25 μg/ml. The application of α-bungarotoxin produced a hyperpolarization of the membrane in the junctional region. The addition of d-tubocurarine failed to produce the hyperpolarization effect. The hyperpolarization effect was also absent when muscles were incubated with the desensitization potentiating drug, SKF-525A. The hyperpolarization effect was unchanged by replacement of Na+ with guanidine and was absent following the replacement of Na+ with arginine.The data suggest the channel responsible for the hyperpolarization effect is the same as that giving the endplate potential. The results are in agreement with the hypothesis that the hyperpolarization effect reflects a sustained non-quantal release of acetylcholine from the nerve terminal into the synaptic cleft. 相似文献
17.
Contribution of Na+/Ca2+ exchanger to the regulation of myogenic tone in isolated rat small arteries
S. Horiguchi J. Watanabe H. Kato S. Baba T. Shinozaki M. Miura M. Fukuchi Y. Kagaya K. Shirato 《Acta physiologica (Oxford, England)》2001,173(2):167-173
The contribution of the Na+/Ca2+ exchanger to the myogenic vascular tone was examined in rat isolated skeletal muscle small arteries (ASK) with pronounced myogenic tone and mesenteric small arteries (AMS) with little myogenic tone. Myogenic tone was assessed by the vascular inner diameter at transmural pressures of 40 and 100 mmHg. To depress the Na+/Ca2+ exchanger, the extracellular Na+ concentration ([Na+]o) was lowered from 143 to 1.2 mM by substituting choline‐Cl for NaCl. The ASK developed significant myogenic tone and constricted further in low [Na+]o. Nifedipine (1 μM ) reduced both myogenic tone and low [Na+]o‐induced contraction. Because the membrane potential of ASK was not changed by low [Na+]o (–35 ± 2 mV at 143 mM [Na+]o, ?37 ± 3 mV at 1.2 mM [Na+]o), depolarization‐induced Ca2+ influx was not a cause of the low [Na+]o‐induced contraction. The AMS did not develop significant myogenic tone. Although low [Na+]o also constricted AMS, the magnitude of constriction was significantly weaker than that in ASK (17 ± 4 vs. 47 ± 6%, P < 0.01, at 58 mM Na+). With Bay K 8644, AMS developed myogenic tone, and low [Na+]o‐induced constriction was significantly increased. In conclusion, Na+/Ca2+ exchanger may play an important role in regulating myogenic tone, likely via mediating Ca2+‐extrusion. 相似文献
18.
C. Loty C. Huchet‐Cadiou S. Talon S. Choisy W. Hleihel 《Acta physiologica (Oxford, England)》2001,172(1):27-37
This study investigated the effect of caffeine on the sarcolemmal mechanisms involved in intracellular calcium control. Ferret cardiac preparations were treated with ryanodine and thapsigargin in order to eliminate the sarcoplasmic reticulum (SR) function. This treatment abolished caffeine contracture irreversibly in normal solution. The perfusion with K‐free medium that blocked the Na+–K+ pump resulted in a recovery of slow relaxing caffeine contractures similar to Na‐free contractures. The amplitude of caffeine contractures was dependent on the bathing [caffeine]o and [Ca2+]o. Divalent cations Ni2+ and Cd2+, which have an inhibitory effect on the Na+/Ca2+ exchanger, produced dose‐dependent inhibition of caffeine responses with apparent Ki of 780 ± 19 and 132 ± 5 μM , respectively. Caffeine also caused dose‐dependent inhibition of Na‐free contractures (Ki=4.62 ± 1.5 mM ), and the reduction or removal of [Na+]o exerted an inhibitory effect on caffeine contractures (Ki=73.5 ± 17.12 mM ). These experiments indicate that the increase in resting tension following exposure to caffeine was mediated by Na+/Ca2+ exchanger, which represents an additional element of complexity in caffeine action on cardiac muscle. 相似文献
19.
In the present study we have compared the effects of increased intracellular Ca2+ in whole frog skin and isolated epithelium (Rana temporaria). Cellular Ca2+ was increased by the use of the endoplasmic reticulum Ca2+ ATPase inhibitor, thapsigargin. Serosal addition of thapsigargin to the whole frog skin increased the Na+ transport by increasing the apical Na+ permeability. This could be blocked by the addition of indomethacin or by removal of Ca2+ from the serosal solution. The increase in Na+ transport was accompanied by an increased prostaglandin E2 release. This indicated that the response in Na+ transport was due to a Ca2+ dependent activation of the prostaglandin E2 synthesis. Addition of thapsigargin to isolated epithelia inhibited the Na+ transport and had no effect on the prostaglandin E2 release, though the prostaglandin E2 release from the isolated epithelia could be increased by the addition of arachidonic acid. Addition of prostaglandin E2 increased the cAMP contents of the isolated epithelia significantly, whereas thapsigargin had no significant effect on the cAMP level. Our results demonstrate that serosal addition of thapsigargin causes a release of prostaglandin E2 from the dermis below the transporting epithelium. The prostaglandin E2 diffuses to the epithelium where it activates the Na+ transport by increasing cellular cAMP. The epithelium itself does not contribute significantly to the prostaglandin E2 synthesis. Furthermore an increase in intracellular Ca2+ in the epithelial cells without a concomitant increase in prostaglandin E2 release leads to an inhibition of the active Na+-transport. 相似文献
20.
Adrenergic and cholinergic inhibition of Ca2+ channels mediated by different GTP-binding proteins in rat sympathetic neurones 总被引:3,自引:0,他引:3
S. -Y. Song K. Saito K. Noguchi S. Konishi 《Pflügers Archiv : European journal of physiology》1991,418(6):592-600
Effects of acetylcholine (ACh) and noradrenaline (NA) on voltage-gated ion channels of sympathetic neurones acutely dissociated from rat superior cervical ganglion (SCG) were examined using the whole-cell voltage-clamp technique. Depolarizing voltage steps elicited two types of low- and high-voltage-activated (LVA and HVA) Ca2+ currents. Pressure applications of ACh and NA produced concentration-dependent inhibition of the HVA Ca2+ current without affecting the LVA Ca2+ current. The inhibitory action of ACh on the Ca2+ current was blocked by a muscarinic antagonist, atropine. The action of NA was suppressed by an
2-adrenergic antagonist, yohimbine, but not by an
1-adrenergic antagonist, prazosin. Delayed rectifying outward K+ currents and inward rectifying K+ current were not affected by either ACh or NA. Tetrodotoxin-sensitive and -insensitive Na+ currents also remained unaffected under actions of ACh and NA. When recorded with electrode containing guanosine-5-O-(3-thiotriphosphate) (GTP--S), the inhibitory actions of ACh and NA on Ca2+ currents became irreversible. After treatment of SCG neurones with pertussis toxin, the inhibitory action of ACh on the Ca2+ current was almost completely abolished, whereas the action of NA was only partially reduced. The results suggest that ACh and NA differentially inhibit the HVA Ca2+ current via different G proteins coupling muscarinic and
2-adrenergic receptors to Ca2+ channels in rat SCG neurones. 相似文献