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1.
The influence of internal Ca2+ ions has been investigated during intracellular perfusion of isolated neurones from pedal ganglia of Helix pomatia in which serotonin (5-HT) induces a cyclic-adenosine-monophosphate-(cAMP)-dependent enhancement of high-threshold Ca2+ current (I
Ca). Internal free Ca2+ ([Ca2+]i) was varied between 0.01 and 10 M by addition of Ca2+-EGTA [ethylenebis(oxonitrilo)tetraacetate] buffer. Elevation of [Ca2+]i depressed the 5-HT effect. The dose/ effect curve for the Ca2+ blockade had a biphasic character and could be described by the sum of two Langmuir's isotherms for tetramolecular binding with dissociation constants K
d1=0.063 M and K
d2=1 M. Addition of calmodulin (CM) antagonists (50 M trifluoperazine or 50 M chlorpromazine), phosphodiesterase (PDE) antagonists [100 M isobutylmethylxanthine (IBMX) or 5 mM theophylline] and protein phosphatase antagonists [2 M okadaic acid (OA)] in the perfusion solution caused anticalcium action and modified the Ca2+ binding isotherm. Using the effect of OA and IBMX, two components of the total Ca2+ inhibition were separated and evaluated. In the presence of one of these blockers tetramolecular curves with K
d1=0.04 M and K
d2=0.69 M were obtained describing the activation of the retained unblocked enzyme — PDE or calcineurin (CN) correspondingly. The sum of these isotherms gave a biphasic curve similar to that in control. Leupeptin (100 M), a blocker of Ca2+-dependent proteases did not influence the amplitude of 5-HT effect, indicating that channel proteolysis is not involved in the depression. Our findings show that the molecular mechanism of Ca2+-induced suppression of the cAMP-dependent upregulation of Ca2+ channels is due to involvement of two Ca2+-CM-dependent enzymes: PDE reducing the cAMP level, and CN causing channel dephosphorylation. No other processes are involved in the investigated phenomenon at a Ca2+ concentration of less than or equal to 10 M. 相似文献
2.
Hiroyuki Hanai Masaki Kameyama Eizo Kaneko Michiya Fujita 《Pflügers Archiv : European journal of physiology》1991,419(2):184-189
Calcium transport systems of isolated ileal epithelial cells were investigated. The concentration of cytosolic free calcium ions, [Ca2+]i, was monitored with a fluorescent Ca2+ dye, fura-2. The fluorescence intensity ratio (I
340/I
380) was used as an index of [Ca2+]i. [Ca2+]i of the cells suspended in the nominally Ca2+-free solution was estimated at 52±3 nM. Ca2+ uptake was followed for as long as 5 min in the presence of 100–1000 M added CaCl2. Most of the experiments were performed at 200 M CaCl2. The Ca2+ uptake was abolished by 0.8 mM Ni2+ and 50 M Mn2+ and partitally antagonized by 50 M verapamil and 50 M diltiazem but not affected by 20 M nifedipine. The Ca2+ entry was reduced by increasing concentrations of extracellular K+ in the presence of valinomycin, suggesting a voltage-dependent nature of the uptake. On the other hand, the Ca2+ transport doubled in the presence of Bay K8644 (8 M), a Ca2+ channel agonist. The Bay-K-8644-induced uptake was inhibited by either 10 M nifedipine, 10 M verapamil or 10 M diltiazem and was relatively independent of extracellular K+ concentration. These results suggest that there are at least two distinct Ca2+ transport systems in the rat ileal epithelial cells, one resistant to organic Ca2+ channel blockers but relatively sensitive to membrane potential (basal uptake) and another inducible by Bay K 8644 and sensitive to the channel blockers but relatively independent of membrane potential. 相似文献
3.
Li C Fultz ME Parkash J Rhoten WB Wright GL 《Journal of muscle research and cell motility》2001,22(6):521-534
Previous work has shown that stimulation of contraction in A7r5 smooth muscle cells with phorbol ester (PDBu) results in the disassembly and remodeling of the -actin component of the cytoskeleton (Fultz et al., 2000, J Mus Res Cell Motil 21: 775–781). In the present study, we evaluated the effect of increasing intracellular calcium ion concentration [Ca2+]i by A23187 and thapsigargin on - and -actin remodeling. The effects of A23187 and thapsigargin on cell contraction and actin remodeling were effectively identical. The two compounds caused contraction of A7r5 cells that was earlier in onset and more quickly completed than PDBu-induced contractions. Both the - and -actin isoforms were incorporated into stress cables in the resting cell. During the interval of contraction, -actin cables shortened without evidence of disassembly. By comparison, the increase of [Ca2+]i resulted in partial or complete dissolution of -actin cables without further remodeling. In addition, PDBu-mediated -actin remodeling was blocked in the presence of A23187. Increased [Ca2+]i also caused dispersal of -actinin but had no effect on the cellular distribution of talin suggesting the effect was selective for -actin cytoskeletal structure. The incubation of cells in calcium-free media prevented -actin dissolution by A23187/thapsigargin and also blocked PDBu-mediated remodeling. Finally, of six kinase inhibitors investigated, only ML-7 partially blocked the dissolution of -actin cables by increased [Ca2+]i. The results suggest that the sustained elevation of [Ca2+]i beyond a threshold level initiates depolymerization of -actin but not -actin. It further appears that PDBu-induced -actin remodeling requires Ca2+ but increases of [Ca2+]i beyond a threshold level may inhibit this activity. The finding that ML-7 partially inhibits -actin dissolution in the presence of A23187/thapsigargin may be suggesting that myosin light chain kinase (MLCK) plays a role in destabilizing -actin structure in the activated cell. 相似文献
4.
Single channel Ca2+ currents inHelix pomatia neurons 总被引:4,自引:0,他引:4
Unitary Ca2+ currents of TEA injected Helix neurons were recorded in the Giga seal situation (6, 7) from microscopic membrane patches exposed to 50 mM [Ca2+]o, O [Na+]o, 20 mM [TEA+]o and 2.5 M [TTX]o. Constant field assumptions yield a channel permeability of 2.9±1.0×10–14 cm3s–1 corresponding to slope conductances of 5 to 15 pS between 0 and –30 mV. Frequency of occurrence of the units strongly increased with depolarization. Mean open time of the Ca2+ channels was about 3 ms without obvious dependence on voltage. A similar open time was seen with [Ba2+]o, yielding about double the current strength when compared with [Ca2+]o. 相似文献
5.
Gervaise Loirand Pierre Pacaud 《Pflügers Archiv : European journal of physiology》1995,430(3):429-436
Effects of exogenous adenosine 5-triphosphate (ATP) were studied by measurements of intracellular Ca2+ concentration ([Ca2+]i) and membrane currents in myocytes freshly isolated from the human saphenous vein. At a holding potential of –60 mV, ATP (10 M) elicited a transient inward current and increased [Ca2+]i. These effects of ATP were inhibited by ,-methylene adenosine 5-triphosphate (AMPCPP, 10 M). The ATP-gated current corresponded to a non-selective cation conductance allowing Ca2+ entry. The ATP-induced [Ca2+]i rise was abolished in Ca2+-free solution and was reduced to 30.1±5.5% (n=14) of the control response when ATP was applied immediately after caffeine, and to 23.7±3.8% (n=11) in the presence of thapsigargin. The Ca2+-induced Ca2+ release blocker tetracaine inhibited the rise in [Ca2+]i induced by both caffeine and ATP, with apparent inhibitory constants of 70 M and 100 M, respectively. Of the ATP-induced increase in [Ca2+]i 29.3±3.9% (n=8) was tetracaine resistant. It is concluded that the effects of ATP in human saphenous vein myocytes are only mediated by activation of P2x receptor channels. The ATP-induced [Ca2+]i rise is due to both Ca2+ entry and Ca2+ release activated by Ca2+ ions that enter the cell through P2x receptor channels. 相似文献
6.
Antonio R. Artalejo Antonio G. García Erwin Neher 《Pflügers Archiv : European journal of physiology》1993,423(1-2):97-103
Simultaneous whole-cell patch-clamp and fura-2 fluorescence [Ca2+]i measurements were used to characterize Ca2+-activated K+ currents in cultured bovine chromaffin cells. Extracellular application of histamine (10 M) induced a rise of [Ca2+]i concomitantly with an outward current at holding potentials positive to –80 mV. The activation of the current reflected an increase in conductance, which did not depend on membrane potential in the range –80 mV to –40 mV. Increasing the extracellular K+ concentration to 20 mM at the holding potential of –78 mV was associated with inwardly directed currents during the [Ca2+]i elevations induced either by histamine (10 M) or short voltage-clamp depolarizations. The current reversal potential was close to the K+ equilibrium potential, being a function of external K+ concentration. Current fluctuation analysis suggested a unit conductance of 3–5 pS for the channel that underlies this K+ current. The current could be blocked by apamin (1 M). Whole-cell current-clamp recordings snowed that histamine (10 M) application caused a transient hyperpolarization, which evolved in parallel with the [Ca2+]i changes. It is proposed that a small-conductance Ca2+-activated K+ channel is present in the membrane of bovine chromaffin cells and may be involved in regulating catecholamine secretion by the adrenal glands of various species. 相似文献
7.
P. E. Squires R. F. L. James N. J. M. London M. J. Dunne 《Pflügers Archiv : European journal of physiology》1994,427(1-2):181-183
Using isolated -cells from human islets of Langerhans we have demonstrated that purinergic receptor agonists are functionally coupled to rises in the intracellular calcium ion concentration ([Ca2+]i). The effects of ATP, ADP and AMP have been examined over a range of concentrations, 0.5 to 500M. The actions of ATP were more potent than those of either ADP or AMP suggesting that a P2-type of purinergic receptor operates in these cells. Responses to ATP were concentration-related, but exhibited marked desensitisation at high concentrations (>100M). Purinergic receptor agonists elevate [Ca2+]i by mechanisms that involve both Ca2+ influx and Ca2+ mobilisation from intracellular stores. The physiological significance of our data has been discussed, and related to previous studies carried out upon rodent and clonal insulin-secreting cells. 相似文献
8.
Enzymatically dispersed smooth muscle cells of the guinea-pig portal vein were studied by the patch-clamp technique. They were found to have Ca2+-dependent K+ channels with the typical properties of the BK channel, i.e. a reversal potential at the calculated equilibrium potential for K+ ions, a striking voltage dependence, and a conductance of approximately 200 pS ([K+]0 50 mM, [K+]i 150 mM, positive patch potentials). Tedisamil, a new bradycardic agent with an inhibitory action on K+ currents in heart muscle, reduced the open probability of the BK channels concentration-dependently (1–100 M) when applied at the cytosolic side of membrane inside-out patches. At 100 M [Ca2+]i, the IC50 of tedisamil was 13.8 M (¯x, n=5). Tedisamil increased the frequency of channel closures, and reduced the mean duration of openings from 8 ms to < 1 ms, while the mean duration of closures within bursts (1–2 ms) was not altered. Tedisamil did not affect long closures (> 160 ms) between bursts, either. The mean time of residence of tedisamil at the BK channel was estimated to be 1–2ms. Hence, tedisamil, in comparison to the slow blocker Ba2+ and the fast blocker tetraethylammonium, holds the position of an intermediate K+ channel blocker.Supported by the Deutsche Forschungsgemeinschaft 相似文献
9.
U. M. Rose R. J. M. Bindels A. Vis J. W. C. M. Jansen C. H. Van Os 《Pflügers Archiv : European journal of physiology》1993,423(5-6):378-386
Ca2+ channel blockers (CCB) have been shown to be protective against ischaemic damage of the kidney, suggesting an important role for intracellular Ca2+ ([Ca2+]i) in generating cell damage. To delineate the mechanism behind this protective effect, we studied [Ca2+]i in cultured proximal tubule (PT) cells during anoxia in the absence of glycolysis and the effect of methoxyverapamil (D600) and felodipine on [Ca2+]i during anoxia. A method was developed whereby [Ca2+]i in cultured PT cells could be measured continuously with a fura-2 imaging technique during anoxic periods up to 60 min. Complete absence of O2 was realised by inclusion of a mixture of oxygenases in an anoxic chamber. [Ca2+]i in PT cells started to rise after 10 min of anoxia and reached maximal levels at 30 min, which remained stable up to 60 min. The onset of this increase and the maximal levels reached varied markedly among individual cells. The mean values for normoxic and anoxic [Ca2+]i were 118±2 (n=98) and 662±22 (n=160) nM, respectively. D600 (1 M), but not felodipine (10 M), significantly reduced basal [Ca2+]i in normoxic incubations. During anoxia 1 M and 100 M D 600 significantly decreased anoxic [Ca2+]i levels by 22 and 63% respectively. Felodipine at 10 M was as effective as 1 M D600. Removal of extracellular Ca2+ and addition of 0.1 mM La3+ completely abolished anoxia-induced increases in [Ca2+]i. We conclude that anoxia induces increases in [Ca2+]i in rabbit PT cells in primary culture, which results from Ca2+ influx. Since this Ca2+ influx is partially inhibited by low doses of CCBs, Ltype Ca2+ channels may be involved. 相似文献
10.
Mark S. Kirby Robert W. Hadley W. J. Lederer 《Pflügers Archiv : European journal of physiology》1994,427(1-2):169-177
We have constructed a modular instrument to measure intracellular [Ca2+] ([Ca2+]i) in single isolated cells while simultaneously imposing step changes in [Ca2+]i using caged Ca2+. By combining the outputs of a xenon arc lamp with a frequency-tripled (Nd: YAG) laser, the instrument can operate with low maintained illumination to measure [Ca2+]i using a ratiometric Ca2+-sensitive fluorophore and also activate the release of Ca2+ from a caged-Ca2+ compound with a high energy pulse of ultraviolet light. This instrument is simple to assemble, introduces little electrical noise, provides a wide range of illumination power, produces only moderate photobleaching of the Ca2+ indicator and can be readily adapted to diverse cellular preparations. We demonstrate the use of this system to measure step changes in [Ca2+]i in adult rat ventricular myocytes and a human embryonic kidney cell line (293 cells) in culture. 相似文献
11.
Jesper Gromada Tino D. Jørgensen Steen Dissing 《Pflügers Archiv : European journal of physiology》1995,429(6):751-761
Stimulation of rat lacrimal acinar cells with acetylcholine (ACh) and the -adrenergic agonist isoprenaline causes a rapid increase in inositol phosphates with 1–4 phosphate groups, resulting in release of Ca2+ from intracellular stores. Stimulation with the -adrenergic agonist phenylephrine, however, causes a release of Ca2+ from internal stores which is 36% of that observed with ACh stimulation, but without inositol phosphate production. This Ca2+ rise was completely inhibited by 100 M ryanodine. Adrenaline (causing activation of both - and -adrenergic receptors) induces a Ca2+ release with inositol phosphate synthesis identical to that occuring in the -adrenergic response. Thus, the signalling pathway for -adrenergic stimulation occurs via a path different from that which releases Ca2+ via muscarinic cholinergic and -adrenergic stimulation. In permeabilized lacrimal acinar cells cyclic adenosine 5-diphosphoribose (cADP-ribose) and inositol 1,4,5-trisphosphate [Ins(1,4,5)P
3] cause release of Ca2+ from intracellular stores. The Ca2+ release evoked by cADP-ribose, but not by Ins(1,4,5)P
3, was abolished by 100 M ryanodine, implicating a possible involvement of cADP-ribose in phenylephrine-induced Ca2+ signalling. When the intracellular free Ca2+ concentration ([Ca2+]i) is raised by application of ionomycin, inositol phosphates are synthesized with a half-maximal effect seen at 425 nM. In contrast, loading cells with the Ca2+ chelator 1,2-bis(2-aminophenoxy) ethane-N,N,N,N-tetraacetic acid (BAPTA) reduced the adrenaline-induced inositol phosphate synthesis by 27%. The stimulation-induced rise in [Ca2+]i, therefore, appears to cause further synthesis of inositol phosphates, thereby amplifying the receptor-mediated response. 相似文献
12.
E. Schlatter I. Ankorina S. Haxelmans R. Kleta 《Pflügers Archiv : European journal of physiology》1995,430(5):721-728
Diadenosine polyphosphates (Ap
n
A) are known to influence cellular Ca2+ activity ([Ca2+]i) in several cells. Their vasoactive potency has been described in various systems including the kidney. We examined the effects of diadenosine polyphosphates, adenosine 5-triphosphate (ATP) and angiotensin II (Ang II) on cytosolic Ca2+ activity of mesangial cells (MC) in culture obtained from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. [Ca2+]i was measured as a fluorescence ratio F
340/F
380 with the fura-2 technique using three excitation wavelengths (340 nm, 360 nm and 380 nm) and a photon counting tube. Resting [Ca2+]i was not significantly different in MC from WKY and SHR rats and was measured as 132±9 nmol/l (n=65) and 114±12 nmol/l (n=36), respectively. Diadenosine polyphosphates (Ap3A–Ap6A) increased [Ca2+]i transiently with an initial peak and a secondary plateau phase comparable to the effects of ATP or Ang II. Increases in [Ca2+]i induced by all these agonists were not significantly different between MC of WKY and SHR rats. ATP, Ap3A, Ap4A, Ap5A, Ap6A (each 5 mol/l) increased the fura-2 fluorescence ratio initially by 0.66±0.09 (n=33), 0.52±0.08 (n=18), 0.25±0.05 (n=16), 0.09±0.06 (n=7), 0.09±0.04 (n=11), respectively. A half-maximal initial increase in the fura-2 fluorescence ratio was reached at 22 nmol/l, 0.9 mol/l, 2.0 mol/l and 4.0 mol/l with Ang II, Ap3A, ATP and Ap4A, respectively. Ap4A (100 mol/l, n=18) led to a reversible contraction of MC. Diadenosine polyphosphates increase [Ca2+]i in rat MC, in a similar manner to ATP or Ang II and lead to a contraction of MC, suggesting that these nucleotides are also involved in the control of glomerular haemodynamics. 相似文献
13.
Indu S. Ambudkar James E. Melvin Bruce J. Baum 《Pflügers Archiv : European journal of physiology》1988,412(1-2):75-79
In rat parotid acinar cells, maximal 1-adrenergic receptor stimulation (10–5 M epinephrine +10–5 M propranolol) leads to a rapid (<10 s), 4–5-fold elevation in cytosolic Ca2+ ( 800 nM at peak) which decreases to 50% of peak Ca2+ by 3–4 min. Similarly, cells preloaded with36Cl– show a rapid (<10 s) 35–50% loss of36Cl– which returns to 80% of resting values in 3–4 min. Both responses are dependent on epinephrine, with half-maximal effects achieved at 2×10–7 M and 2×10–6 M agonist for Cl– and Ca2+, respectively. In the presence of low extracellular Ca2+ (i.e. with EGTA), the initial rapid changes in cellular Ca2+ and Cl– are unaltered. However, cellular Ca2+ and Cl– levels return to basal values sooner than when extracellular Ca2+ is present (within 2 and 3 min, respectively). Maximal epinephrine-induced Ca2+ and Cl– responses are unaffected by the 2-adrenergic antagonist, yohimbine, are completely blocked by the 1-adrenergic antagonist, SZL-49, and are similar to ion fluxes induced by maximal muscarinic-cholinergic receptor stimulation (10–5 M carbachol). The data suggest that a close association exists between mobilization of intracellular Ca2+ and Cl– content in rat parotid acinar cells after 1-adrenocetor stimulation. 相似文献
14.
N. Hara M. Ichinose M. Sawada T. Maeno 《Pflügers Archiv : European journal of physiology》1991,419(3-4):371-379
Responses to adrenaline in mouse peritoneal macrophages were investigated with perforated and cell-attached patch-clamp recording, and with a combination of the perforated-patch recording and fura-2 fluorescence measurements. Extracellularly applied adrenaline induced a transient outward current (4–10s in duration, 100–500 pA in amplitude) at –40 mV associated with a marked increase in conductance. The adrenaline-induced current [I
o (Adr)] reversed polarity near –80 mV. The reversal potential depended distinctly on the external K+ concentration but not on external Cl– concentration. Removal of external Ca2+ did not affect I
o(Adr) within 2–4 min but subsequent responses to adrenaline were progressively depressed. In contrast, treatment with an intracellular Ca2+ chelator, the acetoxymethyl ester of 1,2-bis-(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid completely abolished I
o(Adr). Furthermore, I
o(Adr) was blocked by bath-applied quinidine and charybdotoxin, but not by tetraethylammonium or apamin. Extracellular application of an
1-adrenoceptor agonist phenylephrine and of noradrenaline mimicked I
o(Adr). On the other hand, I
o(Adr) was antagonized by a non-selective -adrenoceptor antagonist phentolamine (0.2 M) and an
1-adrenoceptor antagonist prazosin (0.2 M), but was not affected by an 2-adrenoceptor antagonist yohimbine (1 M) or a -adrenoceptor antagonist propranolol (1 M). Cell-attached single-channel recordings with the pipette solution containing 145 mM KCl revealed the activation of single-channel currents with a conductance of 40 pS during application of adrenaline outside the patch. Parallel measurements of membrane current and fura-2 fluorescence in the same cell demonstrated a correlation between the rise in [Ca2+]i and an increase in K+ conductance. Therefore, it is concluded that adrenaline activates a Ca2+-dependent K+ conductance by release of Ca2+ from internal stores through an activation of an
1-adrenoceptor. 相似文献
15.
Jeffrey P. Gardner F. P. J. Diecke 《Pflügers Archiv : European journal of physiology》1988,412(3):231-239
The effects of pH (from pH values 6.50–7.10) on isometric tension development and relaxation were investigated in Triton X-100 skinned rat caudal artery. Helically cut skinned strips contracted in 21 M Ca2+ were studied with respect to maximal isometric tension (Po) and rate of contraction (T0.5C), and following relaxation in 18 nm Ca2+, the rate of relaxation (T0.5R). Acidic pH (pH 6.50) decreased Po to 87% of isometric force obtained at pH 6.90, and increased the rate of contraction as shown by a decrease of T0.5C to 80%. In contrast, T0.5R increased 4.5-fold, indicating that with a change of only 0.40 pH units, relaxation rates were dramatically decreased. pCa-tension curves at pH values 6.50, 6.70, 6.90 and 7.10 indicated no significant shift in half maximal activation (pCa50) between pH 6.50 and 6.70, but a significant (P<0.01) shift in pCa50 between pH 6.70 ([Ca2+]=0.46 M) and pH 7.10 ([Ca2+]=0.87 M). Compared to contractions at pH 6.90, myosin light chain (LC20) phosphorylation at pH 6.50 was significantly greater at 30 and 60 s into contraction but not significantly different at 3–10 min. At both pH 6.50 and 6.90, dephosphorylation was rapid and substantially preceded relaxation; LC20 dephosphorylation and relaxation occurred more rapidly at pH 6.90 than at 6.50. At pH 6.50 and 6.90, relax solutions made with increased Ca2+ buffering capacity showed no effect in enhancing T0.5R, suggesting the difference between relaxation rates was not due to Ca2+ diffusion limitations from the skinned strip. We suggest pH changes can after the contractile and relaxation responses in vascular smooth muscle and these effects may be related to LC20 phosphorylation/dephosphorylation regulatory mechanisms.Abbreviations PIPES
piperazine-N,N-bis-(2-ethanesulfonic acid)
- EGTA
5-ethyleneglycol-bis-(-aminoethyl ether)-N,N,N,N-tetraacetic acid
- DTT
dithiothreitol
- HDTA
1,6-diaminohexane-N,N,N,N-tetraacetic acid
- SDS
sodium dodecyl sulfate
J. P. Gardner was supported in part by an AHA N.J. affiliate postdoctoral fellowship 相似文献
16.
Effects of -adrenoceptor stimulation on intracellular Ca2+ transients and tension were explored in rat ventricular muscles injected with aequorin. Adrenaline (0.05–5.0 M) and isoproterenol (0.05–1.0 M) increased the peak of twitch tension and accelerated relaxation. The former effect depended on Ca2+ concentration in Tyrode's solution ([Ca2+]o) and the stage of the experiment. Low concentrations of these drugs added to normal Tyrode's solution containing 2 mM [Ca2+]o did not potentiate twitch tension in the early stage of the experiments. These drugs increased the peak of the aequorin light signal and slightly accelerated the falling phase of the light especially the tail. Effects of dibutyryl-cyclic AMP (DB-cAMP) (0.1–5.0 mM) and 3-isobutyl-1-methylxanthine (IBMX) (0.01–0.5 mM) were qualitatively similar to those of adrenaline and isoproterenol.Isoproterenol applied at the peak of Na-deficient contracture decreased tension without significantly changing the light signal; similar results were obtained in the presence of ryanodine (1 M).The results were interpreted as follows: The increase of intracellular cAMP induced by -adrenoceptor stimulation facilitated Ca2+ uptake by sarcoplasmic reticulum (SR) and decreased Ca2+ sensitivity of contractile elements. Faster relaxation induced by cAMP was considered to be due to the decrease of Ca2+ sensitivity of contractile elements and faster Ca2+ uptake by SR. The slightly faster falling phase of light transient might be due to the faster Ca2+ uptake by SR, which predominates over the slower fall of [Ca2+]i induced by the decreased Ca2+ sensitivity of the contractile element. 相似文献
17.
Willy Van Driessche David Erlij Isabelle Aelvoet 《Pflügers Archiv : European journal of physiology》1990,417(3):342-348
The role of Ca2+ in the regulation of antidiuretic hormone(ADH)-induced water permeability of the apical membrane of the toad urinary bladder was examined. The effects of modifying Ca2+ entry through the apical membrane of toad urinary bladders on the hydroosmotic water flow H2O) and short circuit current (I
sc) were measured. In most experiments the bladders were treated with small amounts of Ag+ (10–7 mol/l) on the apical side. This treatment was used because previous experiments indicate that it markedly increases alkali-earth cation fluxes through an amiloride-insensitive cation channel in the apical membrane of the urinary bladder. Moreover, when Ca2+ is the major cation in the apical solution of these Ag+-treated bladders, I
sc is mostly due to Ca2+ entry through the apical membrane. Ag+ increased I
sc and simultaneously inhibited H2O in bladders perfused with Ca2+ solutions on the apical side. Addition of La3+ to the apical solution reversed the stimulation of I
sc and the inhibition of H2O produced by Ag+. When bladders were perfused with Ca2+-free solutions on the apical side, addition of Ag+ did not inhibit H2O while the stimulation of cation movements through the amiloride-insensitive cation channel persisted. In bladders perfused with apical Ca2+ solutions and treated with chlorophenyl thio-cyclic adenosine monophosphate (ClPheS-cAMP) the addition of Ag+ did not inhibit H2O while it still increased I
sc. Finally, addition of Ca2+ to the apical solution of bladders not treated with Ag+ reduced H2O. These results taken together with other findings in the literature suggest: (1) Ca2+ entry through the Ag+-treated amiloride-insensitive cation channel of the apical membrane inhibits H2O; (2) the effects of Ca2+ entry are at a regulatory site that precedes the interaction of cAMP with the water channels; (3) it is also possible that Ca2+ entry through the unmodified amiloride-insensitive cation channel may have some inhibitory effect on H2O. 相似文献
18.
Hideaki Katsuyama Shinichi Ito Take Itoh Hirosi Kuriyama 《Pflügers Archiv : European journal of physiology》1991,419(5):460-466
To study the essential features of acetylcholine (ACh)-and caffeine-sensitive cellular Ca2+ storage sites in single vascular smooth muscle cells of the porcine coronary artery, the effects of ryanodine on both ACh- and caffeine-induced Ca2+ mobilization were investigated by measuring intracellular Ca2+ concentration ([Ca2+]i) using Fura 2 in Ca2+-containing or Ca2+-free solution. The resting [Ca2+]i of the cells was 122 nM in normal physiological solution and no spontaneous activity was observed. In a solution containing 2.6 mM Ca2+, 10 M ACh or 128 mM K+ produced a phasic, followed by a tonic, increase in [Ca2+]i but 20 mM caffeine produced only a phasic increase. In Ca2+-free solution containing 0.5 mM ethylenebis(oxonitrilo)tetraacetate (EGTA), the resting [Ca2+]i rapidly decreased to 102 nM within 5 min, and 10 M ACh or 20 mM caffeine (but not 128 mM K+) transiently increased [Ca2+]i. Ryanodine (50 M) greatly inhibited the phasic increase in [Ca2+]i induced by 10 M ACh or 5 mM caffeine and increased the time to peak and to the half decay after the peak in the presence or absence of extracellular Ca2+. By contrast, ryanodine (50 M) enhanced the tonic increase in [Ca2+]i induced by 128 mM K+ and also by 10 M ACh in Ca2+-containing solution. In Ca2+-free solution containing 0.5 mM EGTA, ACh (10 M) failed to increase [Ca2+]i following application of 20 mM caffeine. The level of [Ca2+]i induced by 20 mM caffeine was greatly reduced, but not abolished, following application of 10 M ACh in Ca2+-free solution. These results suggest that both ACh and caffeine release Ca2+ from the ryanodine-sensitive sarcoplasmic reticulum (SR) in smooth muscle cells of the porcine coronary artery. The finding that ryanodine significantly increased the resting [Ca2+]i and inhibited the rate of decline of [Ca2+]i following wasthout of high K+ or ACh in Ca2+-containing solution suggests that SR may negatively regulate the resting [Ca2+]i in smooth muscle cells of the porcine coronary artery. 相似文献
19.
Florian Lang Gillian L Busch Günther Zempel Jens Ditlevsen Matthias Hoch Ute Emerich Dorothee Axel Jürgen Fingerle Sabine Meierkord Horst Apfel Peter Krippeit-Drews Helmut Heinle 《Pflügers Archiv : European journal of physiology》1995,431(2):253-258
Exposure of aortic strips from guinea-pigs to hypotonic extracellular fluid is followed by marked vasoconstriction, which is inhibited by D-600 (3 M), a blocker of voltage-sensitive Ca2+ channels. Conventional electrophysiology, patch-clamp studies, pH determination with 2, 7 bis(2-carboxyethyl)-5, 6-carboxyfluorescein (BCECF) and Ca2+ measurements with Fura-2 have been performed on smooth muscle cells cultured either from rat or human aorta to further elucidate the underlying mechanisms. Exposure of the cells to a 25% hypotonic extracellular fluid leads to a rapid and fully reversible depolarization, paralleled by an increase of the selectivity and conductance of the cell membrane to Cl–, an acidification of the cytoplasm and an increase of intracellular Ca2+ concentration ([Ca2+]i). The latter is inhibited by the Ca2+ channel blocker D-600 (1–3 M). It is concluded that osmotic cell swelling leads to the activation of an anion channel. The subsequent depolarization of the cell membrane activates voltage-sensitive Ca2+ channels which increases [Ca2+]i, thus stimulating the contraction of vascular smooth muscle cells. 相似文献
20.
Gerald O. Carrier Stephen R. Ikeda 《Pflügers Archiv : European journal of physiology》1992,421(1):7-16
Inward membrane currents of sympathetic neurons acutely dispersed from coeliac-superior mesenteric ganglia (C-SMG) of adult rats were characterized using the whole-cell variant of the patch-clamp technique. Current-clamp studies indicated that C-SMG neurons retained electrical properties similar to intact ganglia. Voltage-clamp studies designed to isolate Na+ currents revealed that tetrodotoxin (TTX, 1 M) completely inhibited the large transient inward current. Half activation potential (V
h) and slope factor (K) were –26.8 mV and 6.1 mV, respectively. Inactivation parameters for V
h and K were –65 mV and 8.2 mV, respectively. Voltage-clamp studies also revealed a high-voltage-activated sustained inward Ca2+ current which was blocked by the removal of external Ca2+ or the presence of Cd2+ (0.1 mM). The dihydropyridine agonist, (+)202–791 (1 M), caused a small increase (20%) in the amplitude of the Ca2+ current at more negative potentials and markedly prolonged the tail currents. -Conotoxin GIVA (, CgTX, 15 M) caused a 66% inhibition of the high-voltage-activated Ca2+ current amplitude. Norepinephrine (1 M) caused a 49% reduction in the peak Ca2+ current. This study is the first demonstration that dispersed C-SMG neurons from adult rats retain electrical characteristics similar to intact ganglia. A TTX-sensitive Na+ current as well as a high voltage-activated sustained Ca2+ current underlie the inward current in C-SMG neurons. The macroscopic Ca2+ current is composed of a small dihydropyridinesensitive (L-type current) and a large -CgTx-sensitive (N-type current) component. Thus, acutely dispersed CSMG neurons are suitable for examining the biophysical properties and modulation of membrane currents of adult prevertebral sympathetic neurons in normal and diseased states. 相似文献