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1.
Microinjection of inositol 1,4,5-trisphosphate (InsP
3) into intact skeletal muscle fibers isolated from frogs (Rana temporaria) increased resting cytosolic Ca2+ concentration ([Ca2+]i) as measured by double-barreled Ca2+-selective microelectrodes. In contrast, microinjection of inositol 1-phosphate, inositol 1,4-biphosphate, and inositol 1,4,5,6-tetrakisphosphate
did not induce changes in [Ca2+]i. Incubation in low-Ca2+ solution, or in the presence of L-type Ca2+ channel blockers did not affect InsP
3-induced release of cytosolic Ca2+. Neither ruthenium red, a blocker of ryanodine receptor Ca2+-release channels, nor cytosolic Mg2+, a known inhibitor of the Ca2+-induced Ca2+-release process, modified the InsP
3-induced release of cytosolic Ca2+. However, heparin, a blocker of InsP
3 receptors, inhibited InsP
3-induced release of cytosolic Ca2+. Also, pretreatment with dantrolene or azumulene, two inhibitors of cytosolic Ca2+ release, reduced [Ca2+]i, and prevented InsP
3 from inducing release of cytosolic Ca2+. Incubation in caffeine or lengthening of the muscle increased [Ca2+]i and enhanced the ability of InsP
3 to induce release of cytosolic Ca2+. These results indicate that InsP
3, at physiological concentrations, induces Ca2+ release in intact muscle fibers, and suggest that the InsP
3-induced Ca2+ release is regulated by [Ca2+]i. A Ca2+-dependent effect of InsP
3 on cytosolic Ca2+ release could be of importance under physiological or pathophysiological conditions associated with alterations in cytosolic
Ca2+ homeostasis.
Received: 15 December 1995/Received after revision and accepted: 10 May 1996 相似文献
2.
Increase in glucose is known to elevate the concentration of cytoplasmic Ca2+ ([Ca2+]i) in pancreatic β‐cells and stimulate insulin secretion. However, rise of glucose can also lower [Ca2+]i and inhibit insulin release. In the present review, we examine the mechanisms for this inhibition and highlight its importance for the healthy β‐cell and the development of diabetes. It is possible to distinguish between 60 and 90 s of prompt inhibition and the late inhibition seen after the first‐phase peak of insulin release. The introductory inhibition is characteristic of the healthy β‐cell and mediated by sequestration of [Ca2+]i in the endoplasmic reticulum. This inhibition is easily seen in studies of isolated islets but too brief to be detected in a conventional intravenous glucose tolerance test. Coupled to simultaneous rise of glucagon, the introductory suppression of insulin release is the starting point for the antiphase relation between the subsequent insulin and glucagon pulses. Another effect of the initial suppression is to increase the pool of readily releasable granules responsible for the first‐phase release of insulin. The presence of late inhibition of insulin release is an indicator of β‐cell dysfunction. Patients with type 2 diabetes often respond to intravenous bolus injection of glucose with 5–10 min of late suppression of circulating insulin. 相似文献
3.
Force development in skeletal muscle is driven by an increase in myoplasmic free [Ca2+] ([Ca2+]i) due to Ca2+ release from the sarcoplasmic reticulum (SR). The magnitude of [Ca2+]i elevation during stimulation depends on: (a) the rate of Ca2+ release from the SR, (b) the rate of Ca2+ uptake by the SR, and (c) the myoplasmic Ca2+ buffering. We have used fluorescent Ca2+ indicators to measure [Ca2+]i in intact, single fibres from mouse and Xenopus muscles under conditions where one or more of the above factors are changed. The following interventions resulted in increased tetanic [Ca2+]i: β-adrenergic stimulation, which potentiates the SR Ca2+ release; application of 2,5-di(tert-butyl)-1,4-benzohydroquinone, which inhibits SR Ca2+ pumps; application of caffeine, which facilitates SR Ca2+ release and inhibits SR Ca2+ uptake; early fatigue, where the rate of SR Ca2+ uptake is reduced; acidosis, which reduces both the myoplasmic Ca2+ buffering and the rate of SR Ca2+ uptake. Reduced tetanic [Ca2+]i was observed in late fatigue, due to reduced SR Ca2+ release, and in alkalosis, due to increased myoplasmic Ca2+ buffering. Force is monotonically related to [Ca2+]i, but depends also on the myofibrillar Ca2+ sensitivity and the maximum force cross-bridges can produce. This is clearly illustrated by changes of intracellular pH where, despite a lower tetanic [Ca2+]i, tetanic force is higher in alkalosis than acidosis due to increases of myofibrillar Ca2+ sensitivity and maximum cross-bridge force. 相似文献
4.
P.-S. HU 《Acta physiologica (Oxford, England)》1993,148(2):115-123
Levels of [Ca2+]i in rat cortex synaptosomes were measured using the Ca2+indicator Fura-2. Ca2+influx was induced by veratridine in a concentration-dependent manner (1–10 μm ). The resulting increase in [Ca2+]i was inhibited by tetrodotoxin (TTX). K+(18 mm ) increased the [Ca2+]i which was not influenced by TTX. K+-channel blockers such as 4-aminopyridine, α-and δ-dendrotoxin per se were ineffective. The veratridineinduced Ca2+influx in synaptosomes was reduced by L-type Ca2+-channel blockers, such as felodipine, nifedipine and PN-200-110, verapamil and diltiazem. ω-Conotoxin, an N-type Ca2+-channel blocker, did not inhibit the veratridine-stimulated [Ca2+]i increase. Bay K 8644, an L-channel agonist, stimulated an increase of [Ca2+]i in synaptosomes which was not sensitive to TTX. R-N6-Phenyl-isopropyl-adenosine (R-PIA) and clonidine, agonists at adenosine A1-receptors and α2-adrenoceptors, respectively, did not influence the veratridinestimulated [Ca2+]i increase. R-PIA did not interact with Bay K 8644-stimulated [Ca2+]i increase in synaptosomes. The results for all the substances used show major differences between the effects on Ca2+influx in synaptosomes and on the electrically evoked neurotransmitter release in slice preparations. Thus, the synaptosome preparation is not a generally applicable experimental model for the study of Ca2+mechanisms of presynaptic neuromodulation. 相似文献
5.
M. SALOMONSSON M. KORNFELD A.M. GUTIERREZ M. MAGNUSSON A.E.G. PERSSON 《Acta physiologica (Oxford, England)》1997,161(3):271-279
The effect of the protein kinase C (PKC) inhibitor chelerytrine (Ch) and the PKC activator 12–0-tetradecanoyl-phorbol-13-acetate (TPA) on the cytosolic calcium concentration ([ Ca2+]i) in isolated intact rabbit afferent arterioles was investigated. [Ca2+]i was measured in the proximal and distal parts of the arteriole. Administration of 1 μM Ch gave rise to a peak followed by an elevated level of [Ca2+]i in both these parts. Neither the peak nor the elevated level of [Ca2+]i was significantly reduced by 1 μM nifedipine. The relative peak increase in [Ca2+]i in response to 1 μM noradrenaline (NA) or to 10 nM angiotensin II (AII) was significantly blunted in both parts after preincubation with 1 μM Ch. Depolarization with 25 mM K+ increased [Ca2+]i in both parts. Preincubation with Ch did not affect the increase in [Ca2+]i induced by 25 mM K+. TPA (10 and 100 nM ) did not significantly affect the basal [Ca2+]i in the afferent arteriole. The [Ca2+]i response to NA or 25 mM K+ was not affected by TPA. We conclude that blockade of PKC increases [Ca2+]i in afferent arteriolar smooth muscle by a mechanism independent of L-type voltage-sensitive calcium channels. Inhibition of PKC blunts the relative increase in [Ca2+]i in response to AII and, to a lesser extent, that induced by NA. We conclude that PKC might be important in modulating the calcium changes that occur in response to these vasoconstrictors. 相似文献
6.
Stanley Misler David W. Barnett Lee C. Falke 《Pflügers Archiv : European journal of physiology》1992,421(2-3):289-291
Sodium azide (NaN3), a reversible inhibitor of mitochondrial respiration, blocks glucose-induced electrical activity and insulin secretion in human pancreatic islet B cells. Here we show that brief (10–15 min) application followed by removal of 3 mM NaN3 results in transient overshoot of electrical activity and insulin secretion even at substimulatory levels of glucose (3–5 mM). In addition, application of NaN3, even at very low [Ca2+]o, reversibly increases cytosolic Ca2+ to levels usually associated with substantial insulin release. These results suggest that (i) metabolic inhibition may reset B cell stimulus-secretion coupling and (ii) a rise in free cytosolic Ca2+, by itself, is not sufficient to trigger insulin secretion.Deceased 相似文献
7.
Carlos Villalobos Javier García-Sancho 《Pflügers Archiv : European journal of physiology》1996,431(3):371-378
Caffeine, a well known facilitator of Ca2+-induced Ca2+ release, induced oscillations of cytosolic free Ca2+ ([Ca2+]i) in GH3 pituitary cells. These oscillations were dependent on the presence of extracellular Ca2+ and blocked by dihydropyridines, suggesting that they are due to Ca2+ entry through L-type Ca2+ channels, rather than to Ca2+ release from the intracellular Ca2+ stores. Emptying the stores by treatment with ionomycin or thapsigargin did not prevent the caffeine-induced [Ca2+]i oscillations. Treatment with caffeine occluded phase 2 ([Ca2+]i oscillations) of the action of thyrotropin-releasing hormone (TRH) without modifying phase 1 (Ca2+ release from the intracellular stores). Caffeine also inhibited the [Ca2+]i increase induced by depolarization with high-K+ solutions (56% at 20 mM), suggesting direct inhibition of the Ca2+ entry through voltage-gated Ca2+ channels. We propose that the [Ca2+]i increase induced by caffeine in GH3 cells takes place by a mechanism similar to that of TRH, i.e. membrane depolarization that increases the firing frequency of action potentials. The increase of the electrical activity overcomes the direct inhibitory effect on voltage-gated Ca2+ channels with the result of increased Ca2+ entry and a rise in [Ca2+]i. Consideration of this action cautions interpretation of previous experiments in which caffeine was assumed to increase [Ca2+]i only by facilitating the release of Ca2+ from intracellular Ca2+ stores. 相似文献
8.
N. Ishii A. W. M. Simpson C. C. Ashley 《Pflügers Archiv : European journal of physiology》1989,414(2):162-170
Effects of 5-hydroxytryptamine (5-HT) and forskolin on intracellular free calcium concentration ([Ca2+]i) were studied in suspensions of fura-2 loaded smooth-muscle cells from the anterior byssus retractor catch muscle ofMytilus edulis. The successive addition of 5 mM carbachol (CCh) and 100 mM KCl to the suspension evoked a transient elevation of [Ca2+]i from the resting value of 124±2.7 nM (mean ± SE,n=18) to 300–400 nM, which was associated with contraction. The change in [Ca2+]i induced CCh was concentration-dependent with the EC50 of 10–5 M. The resting [Ca2+]i was unaffected by 10 M 5-HT. The change in [Ca2+]i induced by 5 mM CCh was suppressed by 5-HT from 167±14.0 (n=11) to 124±14.9 (n=8) nM whereas that induced by 100 mM KCl was enhanced from 321±31.9 to 405±17.6 nM (n=8). 5-HT applied during the decaying phase of the CCh response caused a rapid decline in [Ca2+]i. In both the responses to CCh and KCl, the falling phase was accelerated by 5-HT. 10 M forskolin, a potent activator of adenylate cyclase, mimicked the effects of 5-HT as did a membrane-permeant cyclic AMP analogue, 8-parachlorophenylthio cyclic AMP (cpt-cAMP). Application of 100 M cpt-cAMP partially suppressed the Ca2+
i response to CCh and enhanced that to KCl.d-Tubocurarine (500 M) added during the decaying phase of the response induced by 100 M CCh, caused a rapid decline in [Ca2+]i similar to that caused by both 5-HT and forskolin. In essentially Ca2+-free sea water, or in the presence of 10 M D600 in seawater containing 4 mM, Ca2+, the response to CCh was partially suppressed, whereas that to KCl was completely abolished, demonstrating a CCh-induced release of intracellularly stored Ca2+. The remaining component of the response to CCh, in either Ca2+-free sea water or in the presence of D600, was abolished by both 5-HT and forskolin. The results suggest that 5-HT has multiple effects on [Ca2+]i in the ABRM, and implicate cyclic AMP in this effect, and that one of the mechanisms underlying these responses is the inhibition of an agonist-induced release of stored Ca2+. In addition, that Ca2+
i is at, or close to resting values during the catch state. 相似文献
9.
Geyti CS Odgaard E Overgaard MT Jensen ME Leipziger J Praetorius HA 《Pflügers Archiv : European journal of physiology》2008,455(6):1105-1117
Renal epithelia can be provoked mechanically to release nucleotides, which subsequently increases the intracellular Ca2+ concentration [Ca2+]i through activation of purinergic (P2) receptors. Cultured cells often show spontaneous [Ca2+]i oscillations, a feature suggested to involve nucleotide signalling. In this study, fluo-4 loaded Madin–Darby canine kidney
(MDCK) cells are used as a model for quantification and characterisation of spontaneous [Ca2+]i increases in renal epithelia. Spontaneous [Ca2+]i increases occurred randomly as single cell events. During an observation period of 1 min, 10.9 ± 6.7% (n = 23) of the cells showed spontaneous [Ca2+]i increases. Spontaneous adenosine triphosphate (ATP) release from MDCK cells was detected directly by luciferin/luciferase.
Scavenging of ATP by apyrase or hexokinase markedly reduced the [Ca2+]i oscillatory activity, whereas inhibition of ecto-ATPases (ARL67156) enhanced the [Ca2+]i oscillatory activity. The association between spontaneous [Ca2+]i increases and nucleotide signalling was further tested in 132–1N1 cells lacking P2 receptors. These cells hardly showed any
spontaneous [Ca2+]i increases. Transfection with either hP2Y6 or hP2Y2 receptors revealed a striking degree of oscillations. Similar spontaneous [Ca2+]i increases were observed in freshly isolated, perfused mouse medullary thick ascending limb (mTAL). The oscillatory activity
was reduced by basolateral apyrase and substantially lower in mTAL from P2Y2
knock out mice (0.050 ± 0.020 events per second, n = 8) compared to the wild type (0.147 ± 0.018 events per second, n = 9). These findings indicate that renal epithelia spontaneously release nucleotides leading to P2-receptor-dependent [Ca2+]i oscillations. Thus, tonic nucleotide release is likely to modify steady state renal function.
C. S. Geyti and E. Odgaard contributed equally to the publication. 相似文献
10.
The aim of the present study was to investigate the physiological role of nitric oxide (NO) in mediating secretory processes in rat lacrimal acinar cells. In addition, we wanted to determine whether the acinar cells possess endogenous nitric oxide synthase (NOS) activity by measuring NO production using the fluorescent NO indicator 4,5‐diaminofluorescein (DAF‐2). We initiated investigations by adding NO from an external source by means of the NO‐donor, S‐nitroso‐N‐acetyl‐penicillamine (SNAP). Cellular concentrations of cyclic guanosine 5′‐phosphate (cGMP) ([cGMP]) were measured by radioimmunoassay (RIA), and we found that SNAP induced a fast increase in the [cGMP], amounting to 350% of the [cGMP] in resting cells. Moreover, addition of SNAP and elevating [cGMP] in fura‐2 loaded lacrimal acinar cells, resulted in a cGMP‐dependent protein kinase‐mediated release of Ca2+ from intracellular stores, leading to a rise in the intracellular free Ca2+ concentration ([Ca2+]i). The Mn2+ quenching studies revealed that the Ca2+ release was not accompanied by Ca2+ influx. Finally, we demonstrate that lacrimal acinar cells possess endogenous NOS activity, which is activated by β‐adrenergic stimulation and not by a rise in [Ca2+]i alone. We show that in rat lacrimal acinar cells, NO and cGMP induce Ca2+ release from intracellular stores via G kinase activation. However, the changes in [Ca2+]i are relatively small, suggesting that this pathway plays a modulatory role in Ca2+ signalling, thus not by itself causing fast transient increases in [Ca2+]i. In addition, we suggest that endogenously produced NO activated by β‐adrenergic receptor stimulation, plays an important role in signalling to the surrounding tissue. 相似文献
11.
Integrin stimulation induces calcium signalling in rat cardiomyocytes by a NO-dependent mechanism 总被引:1,自引:1,他引:0
van der Wees CG Bax WH van der Valk EJ van der Laarse A 《Pflügers Archiv : European journal of physiology》2006,451(4):588-595
The myocardial stretch-induced increase in intracellular [Ca2+] ([Ca2+]i) is considered to be caused by integrin stimulation. Myocardial stretch is also associated with increased nitric oxide (NO) formation. We hypothesised that NO is implicated in calcium signalling following integrin stimulation. Integrins of neonatal rat cardiomyocytes were stimulated with a pentapeptide containing the Arg-Gly-Asp (RGD) sequence. [Ca2+]i was measured with Fura2, [NO]i was measured with DAF2 and phosphorylation of focal adhesion kinase (FAK) was monitored with immunofluorescence techniques. Integrin stimulation increased both [NO]i and [Ca2+]i, the latter response being inhibited by ryanodine receptor-2 (RyR2) blockers and by NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NOS, but resistant to GdCl3, diltiazem and wortmannin. Integrin-induced intracellular Ca2+ release thus appears to be independent of the influx of extracellular Ca2+ and phosphatidylinositol-3 kinase activity. In addition, integrin stimulation induced phosphorylation of FAK. Our results provide evidence for an integrin-induced Ca2+ release from RyR2 which is mediated by NO formation, probably via FAK-induced NOS activation. 相似文献
12.
Dual-wavelength microfluorometry with the fura-2 indicator was employed for continuous recordings of cytoplasmic Ca2+ (Ca2+) in individual pancreatic β-cells isolated from ob/ob-mice. When added to a medium containing 3 mmol l-1 glucose, both 10 mmol r1 leucine and 20 mmol l“1 arginine induced rises in Cai2+ with periodic fluctuations. In the case of leucine, this increase was preceded by initial lowering followed by high-amplitude oscillations with a periodicity of 2–0 min. In a glucose-free medium arginine had no effect, and leucine was unable to induce more than a single peak of Cai2+ increase. When present at a concentration of 1 mmol l-1, leucine sometimes induced a couple of high-amplitude oscillations at 3 mmol l-1 glucose but lowered Cai2+ permanently in a glucose-free medium. It is likely that the high-amplitude oscillations of Cai2+ are related to the electrical activity of the β-cells. Provided that some glucose was present, leucine initiated a similar type of Cai2+ response as obtained during glucose-induced insulin release. The observed leucine effect is therefore compatible with a role of glycolysis in generating high-amplitude Cai2+ oscillations and pulsatile insulin release. 相似文献
13.
Regulation of GABA release by depolarisation-evoked Ca2+ transients at a single hippocampal terminal
Fedulova SA Verkhratsky A Veselovsky NS 《Pflügers Archiv : European journal of physiology》2004,448(4):376-382
We correlated dynamic changes in free cytosolic [Ca2+] ([Ca2+]i) within single presynaptic terminals of cultured hippocampal neurones with the postsynaptic GABA-mediated currents. The local changes in [Ca2+]i and evoked inhibitory postsynaptic currents (eIPSCs) were recorded simultaneously using Fura-2 fluorescence and whole-cell patch-clamp respectively. The Ca2+ signals and eIPSCs were evoked by direct extracellular electrical stimulation of a single presynaptic terminal by short depolarising pulses. The presynaptic Ca2+ transient was graded by varying the amplitude of extracellular stimulating pulses. The probability of the release event, P, estimated for each stimulation strength, reached a maximum (P=1) when the Ca2+ signal became maximal and remained at this level at higher stimulation strength, despite the subsequent decrease in the amplitude of the Ca2+ transient. A gradual, linear increase in stimulation amplitude (Vstim) resulted in a bell-shaped dependence of the averaged amplitudes of Ca2+ signals and corresponding averaged amplitudes of eIPSCs. Analysis of the eIPSC demonstrated that the decrease in both the mean eIPSC amplitude and the mean quantal content of release resulted from a reduction in the probability of multivesicular release, i.e. in the disappearance of failures and in the decrease of individual eIPSC amplitude. The Ca2+ signals of similar amplitude resulted in both random and determinate (non-random) neurotransmitter release. We conclude that depolarisation-induced elevation of [Ca2+]i within the terminal is necessary but not sufficient for activation of vesicular release of neurotransmitter. 相似文献
14.
R. Warth I. Thiele M. Bleich R. Greger 《Pflügers Archiv : European journal of physiology》1998,436(1):133-140
In many exocrine glands cytosolic Ca2+ ([Ca2+]i) plays a pivotal role in stimulation-secretion coupling. In the rectal gland of the dogfish Squalus acanthias this appears not to be the case and it is believed that secretion is mainly controlled by the Cl– conductance of the luminal membrane. We have examined this question in a study of isolated in vitro perfused rectal gland
tubules (RGT). Three types of measurements were performed: (1) measurements of [Ca2+]i by the fura-2 technique; (2) measurements of transepithelial electrical parameters, i.e. transepithelial voltage (V
te), transepithelial resistance (R
te), the equivalent short-circuit current (I
sc) and the voltage across the basolateral membrane (V
bl), and (3) whole-cell patch-clamp measurements of cellular voltage (V
m), conductance (G
m) and membrane capacitance (C
m). The data indicates that carbachol (CCH) increases [Ca2+]i by increasing store release and Ca2+ influx. Other agonists, producing cytosolic cAMP, also increased [Ca2+] by enhancing Ca2+ influx. CCH hyperpolarized these cells and enhanced G
m significantly. The effect of CCH on V
te and I
sc was most marked under control conditions and disappeared in RGT otherwise stimulated by agonists that lead to cAMP production.
It is concluded that [Ca2+]i plays a major role in the stimulation of NaCl secretion in RGT by enhancing the basolateral K+ conductance. cAMP-producing agonists enhance [Ca2+]i by increased Ca2+ influx. CCH releases Ca2+ from respective stores. CCH, unlike the cAMP-producing agonists, only increases basolateral K+ conductance. It modulates secretion especially under conditions in which the cAMP pathway is not fully activated.
Received: 25 November 1997 / Received after revision: 19 January 1998 / Accepted: 21 January 1998 相似文献
15.
K. -G. Fischer J. Leipziger P. Rubini-Illes R. Nitschke R. Greger 《Pflügers Archiv : European journal of physiology》1996,432(4):735-740
In HT29 colonic epithelial cells agonists such as carbachol (CCH) or ATP increase cytosolic Ca2+ activity ([Ca2+]i) in a biphasic manner. The first phase is caused by inositol 1,4,5-trisphophate-(Ins P
3-) mediated Ca2+ release from their respective stores and the second plateau phase is mainly due to stimulated transmembraneous Ca2+ influx. The present study was undertaken to examine the effect of increased adenosine 3′,5′-cyclic monophasphate (cAMP) (forskolin
10 μmol/l = FOR) on the Ca2+ transient in the presence of CCH (100 μmol/l). In unpaired experiments it was found that FOR induced a depolarization and
reduced cytosolic Ca2+ ([Ca2+]i, measured as the fura-2 fluorescence ratio 340/380 nm) significantly. Dideoxyforskolin had no such effect. The effect of
FOR was abolished when the cells were depolarized by a high-K+ solution. In further paired experiments utilizing video imaging in conjunction with whole-cell patch-clamp, [Ca2+]i was monitored separately for the patch-clamped cell and three to seven neighbouring cells. In the presence of CCH, FOR reduced
[Ca2+]i uniformly from a fluorescence ratio (345/380) of 2.9 ± 0.12 to 1.8 ± 0.07 in the patch-clamped cell and its neighbours (n = 48) and depolarized the membrane voltage (V
m) of the patch-clamped cells significantly and reversibly from −54 ± 7.4 to −27 ± 5.9 mV (n = 6). In additional experiments V
m was depolarized by 15–54 mV by various increments in the bath K+ concentration. This led to corresponding reductions in [Ca2+]i. Irrespective of the cause of depolarization (high K+ or FOR) there was a significant correlation between the change in V
m and change in [Ca2+]i. These data indicate that the cAMP-mediated attenuation of Ca2+ influx is caused by the depolarization produced by this second messenger.
Received: 12 March 1996/Accepted: 2 April 1996 相似文献
16.
R. Nitschke J. Leipziger R. Greger 《Pflügers Archiv : European journal of physiology》1993,423(3-4):274-279
Cell swelling induced by hypotonic solution led to an osmolality-dependent increase in intracellular Ca2+ activity ([Ca2+]i) in HT29 cells. At moderate reductions in osmolality from 290 to 240 or 225 mosmol/l in most cases only a small monophasic increase of [Ca2+]i to a stable plateau of 10–20 nmol/l above resting [Ca2+]i was observed. Lower osmolalities resulted in a triphasic increase of [Ca2+]i to a peak value. In a first phase after the volume change, lasting 20–40 s, [Ca2+]i increased slowly by about 30 nmol/l. Thereafter [Ca2+]i increased more rapidly within 20–30 s to a peak value. This peak was 189±45 nmol/l (190 mosmol/l, n=9) and 243±41 nmol/l (160 mosmol/l, n=20) above resting [Ca2+]i. The peak was then followed by a decline of [Ca2+]i over the next 2–3 min to a stable plateau value of 28±6 (n=6) and 32±11 nmol/l (n=11) above resting [Ca2+]i at 190 and 160 mosmol/l, respectively. The plateau lasted as long as the hypotonic solution was present. Under Ca2+-free bath conditions the peak value for the cell-swelling-induced [Ca2+]i transient was reached significantly later (60–100 s, compared to 40–60 s under control conditions). The peak values under Ca2+-free conditions were not significantly lower. This indicates that the [Ca2+]i peak was mostly of intracellular origin. No [Ca2+]i plateau phase was observed under Ca2+-free bath conditions. With the use of the fura-2-Mn 2+ quenching technique an increased Ca2+ influx induced by hypotonic cell swelling was shown (160 mosmol/l; n=4). This influx started immediately after or simultaneously with the cell swelling and preceded the [Ca2+]i peak for more than 50 s.This study was supported by DFG grant Gr 480/10. 相似文献
17.
Ludwig Missiaen Masahiro Oike Martin D. Bootman Humbert De Smedt Jan B. Parys Rik Casteels 《Pflügers Archiv : European journal of physiology》1994,428(3-4):283-287
Changes in cytosolic Ca2+ concentration ([Ca2+]i) and in membrane potential were monitored in single A7r5 smooth-muscle cells during spontaneous spiking and after arginine vasopressin stimulation. Spontaneous Ca2+ oscillations, which were associated with the occurrence of action potentials, occurred in about 90% of the confluent monolayers investigated. This spontaneous activity was synchronized amongst all the cells of the monolayer, indicating that the cells were electrically coupled. Arginine vasopressin stimulation produced a [Ca2+]i rise that was about 5 times higher than the amplitude of the spontaneous Ca2+ oscillations and resulted in a subsequent cessation of spontaneous electrical activity and associated Ca2+ spiking, which persisted after [Ca2+]i returned to baseline. Individual cells in the monolayer responded to arginine vasopressin with a different latency. Agonist-induced Ca2+ waves within one cell propagated much more slowly than spontaneous [Ca2+]i rises. We conclude that agonist-induced [Ca2+]i increases in an electrically coupled cell monolayer can be asynchronous. 相似文献
18.
Shigeo Taniguchi Jeannine Marchetti François Morel 《Pflügers Archiv : European journal of physiology》1989,415(2):191-197
Single pieces of fura-2-loaded cortical collecting tubule (CCT) isolated either from normal or adrenalectomized (ADX) rats were superfused in vitro, and the cytosolic calcium concentration ([Ca2+]i) was calculated from fluorescence recordings. The effects of altering the sodium gradient across cell membranes were investigated. Switching external sodium from 164 mM to 27 mM (low [Na+]o) had little effect on [Ca2+]i in normal tubules (106±9 versus 101±9 nM, n=15) whereas it resulted in a large peak of [Ca2+]i in CCT from ADX-rats (270±32 versus 135±11 nM, n=21). Since CCT from ADX rats are known to have a reduced Na-pump activity, the effect of ouabain treatment on CCT from normal rats was also tested. When CCT from normal rats were exposed to 1 mM of ouabain in the presence of 164 mM of [Na+]o, [Ca2+]i increased only moderately (123±15 versus 111±11 nM, n=13); when the low [Na+]o solution was applied to these ouabain-treated tubules, a large and transient increase in [Ca2+]i was obtained (287±38 versus 123±15 nM, n=13). This response was absent with [Ca2+]o=0. The data suggest the presence of 3 Na+/1 Ca2+ exchangers in cell membranes of rat CCT. The calcium flux equation derived by Läuger for the exchanger indicates a non-linear relationship between net calcium flux and driving force which could account for the difference observed here between the poor effect of applying either low [Na+]o or ouabain alone and the large peak of [Ca2+]i induced by combining these two conditions. 相似文献
19.
Aim: The aim of this study was to determine the effects of motilin on [Ca2+]i regulation and its underlying molecular mechanism in cultured antral smooth muscle cells (ASMCs). Methods: Antral cells were isolated and cultured from neonatal rats, and then the [Ca2+]i in these cells was evaluated by calcium fluorescent probe Fluo-3/AM on a laser scanning confocal microscope. Results: We show that motilin dose-dependently increased [Ca2+]i concentration in cultured ASMCs. Pre-incubation of cells with either the calcium antagonist verapamil (10−5 mol L−1) or the calcium chelator Egtazic (EGTA, 0.1 mmol L−1) significantly suppressed motilin (10−6 mol L−1) induced [Ca2+]i increase as indicated by fluorescent intensity. Interestingly, after mixing with the non-selective intracellular calcium release blocker TMB-8 (10−5 mol L−1), guanosine triphosphate regulatory protein antagonist NEM (10−5 mol L−1), phospholipase C (PLC) inhibitor compound 48/80 (1.2 μg mL−1) and ryanodine at high concentration (10−5 mol L−1), the motilin-induced [Ca2+]i increase was only partially blocked. The protein kinase C inhibitor d -sphingosine (10−6 mol L−1), however, did not show any inhibitory effect on motilin-induced [Ca2+]i elevation. Conclusions: Our study suggests that motilin-stimulated [Ca2+]i elevation in ASMCs is probably due to sustained extracellular Ca2+ influx and Ca2+ release from Ca2+ stores via inositol tris-phosphate receptors and ryanodine receptors. Specifically, motilin-induced [Ca2+]i release is accompanied with guanosine triphosphate-binding protein-coupled receptor–PLC–inositol tris-phosphate signalling cascades. 相似文献
20.
Steen Dissing Birgitte Nauntofte Ove Sten-Knudsen 《Pflügers Archiv : European journal of physiology》1990,417(1):1-12
The spatial distribution of intracellular, free Ca2+ ([Ca2+]i) in rat parotid acini was measured by imaging fura-2 fluorescence from individual acinar cells by means of a digital imaging microscope. Upon cholinergic stimulation in a Krebs-Ringer bicarbonate buffer at (37° C), [Ca2+]i increased synchronously at both the basolateral and luminal membranes as well as in all cells of the secretory endpiece, reaching peak [Ca2+]i levels 1 s after stimulation. Atropine addition caused a rapid down-regulation of [Ca2+]i, which, however, never reached prestimulatory levels. When acini were stimulated in a medium containing 5 nM Ca2+, the Ca2+ mobilization arising from internal pools caused an increase in [Ca2+]i predominantly near the basolateral area, where the endoplasmic reticulum is located, and standing Ca2+ gradients were observed for up to 10 s. A mathematical model is developed to simulate the time courses of the Ca2+ profiles through the cytoplasm using estimated values of the Ca2+ diffusion coefficients and the cytosolic Ca2+ buffering capacity. It is concluded that under physiological conditions, the Ca2+ release from the endoplasmic reticulum is responsible for the activation of the basolaterally located K+ channels. Furthermore, Ca2+ influx from the interstitium is responsible for much of the rise in [Ca2+]i near the luminal membranes, where the Cl– channels are supposed to be located. 相似文献