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1.
In fura 2-loaded N1E-115 cells, regulationof intracellular Ca2+ concentration([Ca2+]i) following a Ca2+ loadinduced by 1 µM thapsigargin and 10 µM carbonylcyanidep-trifluoromethyoxyphenylhydrazone (FCCP) wasNa+ dependent and inhibited by 5 mM Ni2+. Incells with normal intracellular Na+ concentration([Na+]i), removal of bath Na+,which should result in reversal of Na+/Ca2+exchange, did not increase [Ca2+]i unlesscell Ca2+ buffer capacity was reduced. When N1E-115 cellswere Na+ loaded using 100 µM veratridine and 4 µg/mlscorpion venom, the rate of the reverse mode of theNa+/Ca2+ exchanger was apparently enhanced,since an ~4- to 6-fold increase in [Ca2+]ioccurred despite normal cell Ca2+ buffering. In SBFI-loadedcells, we were able to demonstrate forward operation of theNa+/Ca2+ exchanger (net efflux ofCa2+) by observing increases (~ 6 mM) in[Na+]i. These Ni2+ (5 mM)-inhibited increases in [Na+]i could onlybe observed when a continuous ionomycin-induced influx ofCa2+ occurred. The voltage-sensitive dyebis-(1,3-diethylthiobarbituric acid) trimethine oxonol was used tomeasure changes in membrane potential. Ionomycin (1 µM) depolarizedN1E-115 cells (~25 mV). This depolarization was Na+dependent and blocked by 5 mM Ni2+ and 250-500 µMbenzamil. These data provide evidence for the presence of anelectrogenic Na+/Ca2+ exchanger that is capableof regulating [Ca2+]i after release ofCa2+ from cell stores. 相似文献
2.
Na(+)/Ca(2+) exchange and its role in intracellular Ca(2+) regulation in guinea pig detrusor smooth muscle 总被引:3,自引:0,他引:3
The role of Na+/Ca2+ exchange inregulating intracellular Ca2+ concentration([Ca2+]i) in isolated smooth muscle cellsfrom the guinea pig urinary bladder was investigated. Incrementalreduction of extracellular Na+ concentration resulted in agraded rise of [Ca2+]i; 50-100 µMstrophanthidin also increased [Ca2+]i. Asmall outward current accompanied the rise of[Ca2+]i in low-Na+ solutions(17.1 ± 1.8 pA in 29.4 mM Na+). The quantity ofCa2+ influx through the exchanger was estimated from thecharge carried by the outward current and was ~30 times that which isnecessary to account for the rise of [Ca2+]i,after correction was made for intracellular Ca2+ buffering.Ca2+ influx through the exchanger was able to loadintracellular Ca2+ stores. It is concluded that the levelof resting [Ca2+]i is not determined by theexchanger, and under resting conditions (membrane potential 50 to60 mV), there is little net flux through the exchanger. However, asmall rise of intracellular Na+ concentration would besufficient to generate significant net Ca2+ influx. 相似文献
3.
Cairns Simeon P.; Hing Wayne A.; Slack John R.; Mills Roland G.; Loiselle Denis S. 《Journal of applied physiology》1998,84(4):1395-1406
The possiblerole of altered extracellular Ca2+concentration([Ca2+]o)in skeletal muscle fatigue was tested on isolated slow-twitch soleusand fast-twitch extensor digitorum longus muscles of the mouse. Thefollowing findings were made. 1) Achange from the control solution (1.3 mM[Ca2+]o)to 10 mM[Ca2+]o,or to nominally Ca2+-freesolutions, had little effect on tetanic force in nonfatigued muscle.2) Almost complete restoration oftetanic force was induced by 10 mM[Ca2+]oin severely K+-depressed muscle(extracellular K+ concentration of10-12 mM). This effect was attributed to a 5-mV reversal of theK+-induced depolarization andsubsequent restoration of ability to generate action potentials(inferred by using the twitch force-stimulation strength relationship).3) Tetanic force depressed bylowered extracellular Na+concentration (40 mM) was further reduced with 10 mM[Ca2+]o.4) Tetanic force loss at elevatedextracellular K+ concentration (8 mM) and lowered extracellular Na+concentration (100 mM) was partially reversed with 10 mM[Ca2+]oor markedly exacerbated with low[Ca2+]o.5) Fatigue induced by using repeatedtetani in soleus was attenuated at 10 mM[Ca2+]o(due to increased resting and evoked forces) and exacerbated at low[Ca2+]o.These combined results suggest, first, that raised[Ca2+]oprotects against fatigue rather than inducing it and, second, that aconsiderable depletion of[Ca2+]oin the transverse tubules may contribute to fatigue. 相似文献
4.
Fang Yu; Condrescu Madalina; Reeves John P. 《American journal of physiology. Cell physiology》1998,275(1):C50
Transfected Chinese hamster ovary cells stably expressing thebovine cardiacNa+/Ca2+exchanger (CK1.4 cells) were used to determine the range of cytosolic Ca2+ concentrations([Ca2+]i)that activateNa+/Ca2+exchange activity. Ba2+ influx wasmeasured in fura 2-loaded, ionomycin-treated cells under conditions inwhich the intracellular Na+concentration was clamped with gramicidin at ~20 mM.[Ca2+]iwas varied by preincubating ionomycin-treated cells with either theacetoxymethyl ester of EGTA or medium containing 0-1 mM added CaCl2. The rate ofBa2+ influx increased in asaturable manner with[Ca2+]i,with the half-maximal activation value of 44 nM and a Hill coefficientof 1.6. When identical experiments were carried out with cellsexpressing a Ca2+-insensitivemutant of the exchanger, Ba2+influx did not vary with[Ca2+]i.The concentration for activation of exchange activity was similar tothat reported for whole cardiac myocytes but approximately an order ofmagnitude lower than that reported for excised, giant patches. Thereason for the difference in Ca2+regulation between whole cells and membrane patches is unknown. 相似文献
5.
Micci M. A.; Christensen Burgess N. 《American journal of physiology. Cell physiology》1998,274(6):C1625
The role of theNa+/Ca2+exchanger in intracellular Ca2+regulation was investigated in freshly dissociated catfish retinalhorizontal cells (HC).Ca2+-permeable glutamate receptorsand L-type Ca2+ channels as wellas inositol 1,4,5-trisphosphate-sensitive and caffeine-sensitiveintracellular Ca2+ stores regulateintracellular Ca2+ in these cells.We used the Ca2+-sensitive dyefluo 3 to measure changes in intracellularCa2+ concentration([Ca2+]i)under conditions in whichNa+/Ca2+exchange was altered. In addition, the role of theNa+/Ca2+exchanger in the refilling of the caffeine-sensitiveCa2+ store followingcaffeine-stimulated Ca2+ releasewas assessed. Brief applications of caffeine (1-10 s) producedrapid and transient changes in[Ca2+]i.Repeated applications of caffeine produced smallerCa2+ transients until no furtherCa2+ was released. Store refillingoccurred within 1-2 min and required extracellularCa2+. Ouabain-induced increases inintracellular Na+ concentration([Na+]i)increased both basal free[Ca2+]iand caffeine-stimulated Ca2+release. Reduction of external Na+concentration([Na+]o)further and reversibly increased[Ca2+]iin ouabain-treated HC. This effect was not abolished by the Ca2+ channel blocker nifedipine,suggesting that increases in[Na+]ipromote net extracellular Ca2+influx through aNa+/Ca2+exchanger. Moreover, when[Na+]owas replaced by Li+, caffeine didnot stimulate release of Ca2+ fromthe caffeine-sensitive store afterCa2+ depletion. TheNa+/Ca2+exchanger inhibitor 2',4'-dimethylbenzamil significantlyreduced the caffeine-evoked Ca2+response 1 and 2 min after store depletion. 相似文献
6.
Evidence for Na+/Ca2+ exchange in intact single skeletal muscle fibers from the mouse 总被引:1,自引:0,他引:1
Balnave Christopher D.; Allen David G. 《American journal of physiology. Cell physiology》1998,274(4):C940
The myoplasmic free Ca2+concentration([Ca2+]i)was measured in intact single fibers from mouse skeletal muscle withthe fluorescent Ca2+ indicatorindo 1. Some fibers were perfused in a solution in which theconcentration of Na+ was reducedfrom 145.4 to 0.4 mM (low-Na+solution) in an attempt to activate reverse-modeNa+/Ca2+exchange (Ca2+ entry in exchangefor Na+ leaving the cell). Undernormal resting conditions, application oflow-Na+ solution only increased[Ca2+]iby 5.8 ± 1.8 nM from a mean resting[Ca2+]iof 42 nM. In other fibers,[Ca2+]iwas elevated by stimulating sarcoplasmic reticulum (SR)Ca2+ release with caffeine (10 mM)and by inhibiting SR Ca2+ uptakewith2,5-di(tert-butyl)-1,4-benzohydroquinone(TBQ; 0.5 µM) in an attempt to activate forward-modeNa+/Ca2+exchange (Ca2+ removal from thecell in exchange for Na+ influx).These two agents caused a large increase in[Ca2+]i,which then declined to a plateau level approximately twice the baseline[Ca2+]iover 20 min. If the cell was allowed to recover between exposures tocaffeine and TBQ in a solution in whichCa2+ had been removed, theincrease in[Ca2+]iduring the second exposure was very low, suggesting thatCa2+ had left the cell during theinitial exposure. Application of caffeine and TBQ to a preparation inlow-Na+ solution produced a large,sustained increase in[Ca2+]iof ~1 µM. However, when cells were exposed to caffeine and TBQ in alow-Na+ solution in whichCa2+ had been removed, a sustainedincrease in[Ca2+]iwas not observed, although[Ca2+]iremained higher and declined slower than in normalNa+ solution. This suggests thatforward-modeNa+/Ca2+exchange contributed to the fall of[Ca2+]iin normal Na+ solution, but whenextracellular Na+ was low, aprolonged elevation of[Ca2+]icould activate reverse-modeNa+/Ca2+exchange. The results provide evidence that skeletal muscle fibers possess aNa+/Ca2+exchange mechanism that becomes active in its forward mode when [Ca2+]iis increased to levels similar to that obtained during contraction. 相似文献
7.
We hypothesized that highextracellular K+ concentration([K+]o)-mediated stimulation ofNa+-K+-Cl cotransporter isoform 1 (NKCC1) may result in a net gain of K+ and Cland thus lead to high-[K+]o-induced swellingand glutamate release. In the current study, relative cell volumechanges were determined in astrocytes. Under 75 mM[K+]o, astrocytes swelled by 20.2 ± 4.9%. This high-[K+]o-mediated swelling wasabolished by the NKCC1 inhibitor bumetanide (10 µM, 1.0 ± 3.1%; P < 0.05). Intracellular36Cl accumulation was increased from acontrol value of 0.39 ± 0.06 to 0.68 ± 0.05 µmol/mgprotein in response to 75 mM [K+]o. Thisincrease was significantly reduced by bumetanide (P < 0.05). Basal intracellular Na+ concentration([Na+]i) was reduced from 19.1 ± 0.8 to16.8 ± 1.9 mM by bumetanide (P < 0.05).[Na+]i decreased to 8.4 ± 1.0 mM under75 mM [K+]o and was further reduced to5.2 ± 1.7 mM by bumetanide. In addition, the recovery rate of[Na+]i on return to 5.8 mM[K+]o was decreased by 40% in the presenceof bumetanide (P < 0.05). Bumetanide inhibitedhigh-[K+]o-induced 14C-labeledD-aspartate release by ~50% (P < 0.05).These results suggest that NKCC1 contributes tohigh-[K+]o-induced astrocyte swelling andglutamate release. 相似文献
8.
Na+/H+ exchangers (NHE) are ubiquitous transporters participating in regulation of cell volume and pH. Cell shrinkage, acidification, and growth factors activate NHE by increasing its sensitivity to intracellular H+ concentration. In this study, the kinetics were studied in dog red blood cells of Na+ influx through NHE as a function of external Na+ concentration ([Na+]o). In cells in isotonic media, [Na+]o inhibited Na+ influx >40 mM. Osmotic shrinkage activated NHE by reducing this inhibition. In cells in isotonic media + 120 mM sucrose, there was no inhibition, and influx was a hyperbolic function of [Na+]o. The kinetics of Na+-inhibited Na+ influx were analyzed at various extents of osmotic shrinkage. The curves for inhibited Na+ fluxes were sigmoid, indicating more than one Na+ inhibitory site associated with each transporter. Shrinkage significantly increased the Na+ concentration at half-maximal velocity of Na+-inhibited Na+ influx, the mechanism by which shrinkage activates NHE. erythrocytes; cell volume regulation; amiloride; kinetics of sodium ion influx 相似文献
9.
Yingst DR Davis J Schiebinger R 《American journal of physiology. Cell physiology》2001,280(1):C119-C125
Because the activity of thesodium pump (Na-K-ATPase) influences the secretion of aldosterone, wedetermined how extracellular potassium (Ko) and calciumaffect sodium pump activity in rat adrenal glomerulosa cells. Sodiumpump activity was measured as ouabain-sensitive 86Rb uptakein freshly dispersed cells containing 20 mM sodium as measured withsodium-binding benzofluran isophthalate. Increasing Ko from4 to 10 mM in the presence of 1.8 mM extracellular calcium (Cao) stimulated sodium pump activity up to 165% andincreased intracellular free calcium as measured with fura 2. Increasing Ko from 4 to 10 mM in the absence ofCao stimulated the sodium pump ~30% and did not increaseintracellular free calcium concentration ([Ca2+]i). In some experiments, addition of1.8 mM Cao in the presence of 4 mM Ko increased[Ca2+]i above the levels observed in theabsence of Cao and stimulated the sodium pump up to 100%.Ca-dependent stimulation of the sodium pump by Ko andCao was inhibited by isradipine (10 µM), a blocker of L-and T-type calcium channels, by compound 48/80 (40 µg/ml) andcalmidizolium (10 µM), which inhibits calmodulin (CaM), and by KN-62(10 µM), which blocks some forms of Ca/CaM kinase II (CaMKII).Staurosporine (1 µM), which effectively blocks most forms of proteinkinase C, had no effect. In the presence of A-23187, a calciumionophore, the addition of 0.1 mM Cao increased[Ca2+]i to the level observed in the presenceof 10 mM Ko and 1.8 mM Cao and stimulated thesodium pump 100%. Ca-dependent stimulation by A-23187 and 0.1 mMCao was not reduced by isradipine but was blocked by KN-62.Thus, under the conditions that Ko stimulates aldosteronesecretion, it stimulates the sodium pump by two mechanisms: directbinding to the pump and by increasing calcium influx, which isdependent on Cao. The resulting increase in[Ca2+]i may stimulate the sodium pump byactivating CaM and/or CaMKII. 相似文献
10.
Integration of rapid cytosolic Ca2+ signals by mitochondria in cat ventricular myocytes 总被引:2,自引:0,他引:2
Sedova M Dedkova EN Blatter LA 《American journal of physiology. Cell physiology》2006,291(5):C840-C850
Decoding of fast cytosolic Ca2+ concentration ([Ca2+]i) transients by mitochondria was studied in permeabilized cat ventricular myocytes. Mitochondrial [Ca2+] ([Ca2+]m) was measured with fluo-3 trapped inside mitochondria after removal of cytosolic indicator by plasma membrane permeabilization with digitonin. Elevation of extramitochondrial [Ca2+] ([Ca2+]em) to >0.5 µM resulted in a [Ca2+]em-dependent increase in the rate of mitochondrial Ca2+ accumulation ([Ca2+]em resulting in half-maximal rate of Ca2+ accumulation = 4.4 µM) via Ca2+ uniporter. Ca2+ uptake was sensitive to the Ca2+ uniporter blocker ruthenium red and the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone and depended on inorganic phosphate concentration. The rates of [Ca2+]m increase and recovery were dependent on the extramitochondrial [Na+] ([Na+]em) due to Ca2+ extrusion via mitochondrial Na+/Ca2+ exchanger. The maximal rate of Ca2+ extrusion was observed with [Na+]em in the range of 2040 mM. Rapid switching (0.251 Hz) of [Ca2+]em between 0 and 100 µM simulated rapid beat-to-beat changes in [Ca2+]i (with [Ca2+]i transient duration of 100500 ms). No [Ca2+]m oscillations were observed, either under conditions of maximal rate of Ca2+ uptake (100 µM [Ca2+]em, 0 [Na+]em) or with maximal rate of Ca2+ removal (0 [Ca2+]em, 40 mM [Na+]em). The slow frequency-dependent increase of [Ca2+]m argues against a rapid transmission of Ca2+ signals between cytosol and mitochondria on a beat-to-beat basis in the heart. [Ca2+]m changes elicited by continuous or pulsatile exposure to elevated [Ca2+]em showed no difference in mitochondrial Ca2+ uptake. Thus in cardiac myocytes fast [Ca2+]i transients are integrated by mitochondrial Ca2+ transport systems, resulting in a frequency-dependent net mitochondrial Ca2+ accumulation. mitochondrial Ca2+; excitation-contraction coupling; cardiomyocytes 相似文献
11.
Palmer Bradley M.; Lynch Joshua M.; Snyder Steven M.; Moore Russell L. 《Journal of applied physiology》1999,86(2):584-591
The effects ofendurance run training onNa+-dependentCa2+ regulation in rat leftventricular myocytes were examined. Myocytes were isolated fromsedentary and trained rats and loaded with fura 2. Contractile dynamicsand fluorescence ratio transients were recorded during electricalpacing at 0.5 Hz, 2 mM extracellular Ca2+ concentration, and 29°C.Resting and peak cytosolic Ca2+concentration([Ca2+]c)did not change with exercise training. However, resting and peak[Ca2+]cincreased significantly in both groups during 5 min of continuous pacing, although diastolic[Ca2+]cin the trained group was less susceptible to this elevation ofintracellular Ca2+. Run trainingalso significantly reduced the rate of[Ca2+]cdecay during relaxation. Myocytes were then exposed to 10 mM caffeinein the absence of external Na+ orCa2+ to trigger sarcoplasmicreticular Ca2+ release and tosuppress cellular Ca2+ efflux.This maneuver elicited an elevated steady-state[Ca2+]c.External Na+ was then added, andthe rate of[Ca2+]cclearance was determined. Run training significantly reduced the rateof Na+-dependent clearance of[Ca2+]cduring the caffeine-induced contractures. These data demonstrate thatthe removal of cytosolic Ca2+ wasdepressed with exercise training under these experimental conditionsand may be specifically reflective of a training-induced decrease inthe rate of cytosolic Ca2+ removalviaNa+/Ca2+exchange and/or in the amount ofCa2+ moved across the sarcolemmaduring a contraction. 相似文献
12.
Michiko Tashiro 《Biophysical journal》2009,96(12):4941-4950
We measured intracellular Mg2+ concentration ([Mg2+]i) in rat ventricular myocytes using the fluorescent indicator furaptra (25°C). In normally energized cells loaded with Mg2+, the introduction of extracellular Na+ induced a rapid decrease in [Mg2+]i: the initial rate of decrease in [Mg2+]i (initial Δ[Mg2+]i/Δt) is thought to represent the rate of Na+-dependent Mg2+ efflux (putative Na+/Mg2+ exchange). To determine whether Mg2+ efflux depends directly on energy derived from cellular metabolism, in addition to the transmembrane Na+ gradient, we estimated the initial Δ[Mg2+]i/Δt after metabolic inhibition. In the absence of extracellular Na+ and Ca2+, treatment of the cells with 1 μM carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone, an uncoupler of mitochondria, caused a large increase in [Mg2+]i from ∼0.9 mM to ∼2.5 mM in a period of 5-8 min (probably because of breakdown of MgATP and release of Mg2+) and cell shortening to ∼50% of the initial length (probably because of formation of rigor cross-bridges). Similar increases in [Mg2+]i and cell shortening were observed after application of 5 mM potassium cyanide (KCN) (an inhibitor of respiration) for ≥90 min. The initial Δ[Mg2+]i/Δt was diminished, on average, by 90% in carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone-treated cells and 92% in KCN-treated cells. When the cells were treated with 5 mM KCN for shorter times (59-85 min), a significant decrease in the initial Δ[Mg2+]i/Δt (on average by 59%) was observed with only a slight shortening of the cell length. Intracellular Na+ concentration ([Na+]i) estimated with a Na+ indicator sodium-binding benzofuran isophthalate was, on average, 5.0-10.5 mM during the time required for the initial Δ[Mg2+]i/Δt measurements, which is well below the [Na+]i level for half inhibition of the Mg2+ efflux (∼40 mM). Normalization of intracellular pH using 10 μM nigericin, a H+ ionophore, did not reverse the inhibition of the Mg2+ efflux. From these results, it seems likely that a decrease in ATP below the threshold of rigor cross-bridge formation (∼0.4 mM estimated indirectly in the this study), rather than elevation of [Na+]i or intracellular acidosis, inhibits the Mg2+ efflux, suggesting the absolute necessity of ATP for the Na+/Mg2+ exchange. 相似文献
13.
Pei Jian-Ming; Yu Xiao-Chun; Bian Jin-Song; Wong Tak-Ming 《American journal of physiology. Cell physiology》1999,277(3):C492
To study the effects of -opioid receptor stimulation onintracellular Ca2+ concentration([Ca2+]i)homeostasis during extracellular acidosis, we determined the effects of-opioid receptor stimulation on[Ca2+]iresponses during extracellular acidosis in isolated single ratventricular myocytes, by a spectrofluorometric method. U-50488H (10-30 µM), a selective -opioid receptor agonist, dosedependently decreased the electrically induced[Ca2+]itransient, which results from the influx ofCa2+ and the subsequentmobilization of Ca2+ from thesarcoplasmic reticulum (SR). U-50488H (30 µM) also increased theresting[Ca2+]iand inhibited the[Ca2+]itransient induced by caffeine, which mobilizesCa2+ from the SR, indicating thatthe effects of the -opioid receptor agonist involved mobilization ofCa2+ from its intracellular poolinto the cytoplasm. The Ca2+responses to 30 µM U-50488H were abolished by 5 µMnor-binaltorphimine, a selective -opioid receptorantagonist, indicating that the event was mediated by the -opioidreceptor. The effects of the agonist on[Ca2+]iand the electrically induced[Ca2+]itransient were significantly attenuated when the extracellular pH(pHe) was loweredto 6.8, which itself reduced intracellular pH(pHi) and increased[Ca2+]i.The inhibitory effects of U-50488H were restored during extracellular acidosis in the presence of 10 µM ethylisopropyl amiloride, a potentNa+/H+exchange blocker, or 0.2 mM Ni2+,a putativeNa+/Ca2+exchange blocker. The observations indicate that acidosismay antagonize the effects of -opioid receptor stimulation viaNa+/H+andNa+/Ca2+exchanges. When glucose at 50 mM, known to activate theNa+/H+exchange, was added, both the resting[Ca2+]iand pHi increased. Interestingly,the effects of U-50488H on [Ca2+]iand the electrically induced[Ca2+]itransient during superfusion with glucose were significantly attenuated; this mimicked the responses during extracellular acidosis. When a high-Ca2+ (3 mM) solutionwas superfused, the resting[Ca2+]iincreased; the increase was abolished by 0.2 mMNi2+, but thepHi remained unchanged. Like theresponses to superfusion with high-concentration glucose andextracellular acidosis, the responses of the[Ca2+]iand electrically induced[Ca2+]itransients to 30 µM U-50488H were also significantly attenuated. Results from the present study demonstrated for the first time thatextracellular acidosis antagonizes the effects of -opioid receptorstimulation on the mobilization ofCa2+ from SR. Activation of bothNa+/H+andNa+/Ca2+exchanges, leading to an elevation of[Ca2+]i,may be responsible for the antagonistic action of extracellular acidosis against -opioid receptor stimulation. 相似文献
14.
Palmer Bradley M.; Thayer Anne M.; Snyder Steven M.; Moore Russell L. 《Journal of applied physiology》1998,85(6):2159-2168
The effects of run endurance training and fura 2 loading on the contractile function andCa2+ regulation of rat leftventricular myocytes were examined. In myocytes not loaded with fura 2, the maximal extent of myocyte shortening was reduced with trainingunder our pacing conditions [0.5 Hz at 2.0 and 0.75 mM externalCa2+ concentration([Ca2+]o)], although training had noeffect on the temporal characteristics. The "light" loading ofmyocytes with fura 2 markedly suppressed (~50%) maximal shorteningin the sedentary and trained groups, although the temporalcharacteristics of myocyte shortening were significantly prolonged inthe trained group. No discernible differences in the dynamiccharacteristics of the intracellularCa2+ concentration([Ca2+]) transientwere detected at 2.0 mM[Ca2+]o, althoughpeak [Ca2+] and rateof [Ca2+] rise duringcaffeine contracture were greater in the trained state at 0.75 mM[Ca2+]o. We concludethat training induced a diminished myocyte contractile function underthe conditions studied here and a more effective coupling of inwardCa2+ current to sarcoplasmicreticulum Ca2+ release at low[Ca2+]o,and that fura 2 and its loading vehicle DMSO significantly alter theintrinsic characteristics of myocyte contractile function andCa2+ regulation. 相似文献
15.
Naro F De Arcangelis V Coletti D Molinaro M Zani B Vassanelli S Reggiani C Teti A Adamo S 《American journal of physiology. Cell physiology》2003,284(4):C969-C976
Cytoplasmic Ca2+concentration ([Ca2+]i) variation is akey event in myoblast differentiation, but the mechanism by which itoccurs is still debated. Here we show that increases of extracellular Ca2+ concentration ([Ca2+]o)produced membrane hyperpolarization and a concentration-dependent increase of [Ca2+]i due to Ca2+influx across the plasma membrane. Responses were not related toinositol phosphate turnover and Ca2+-sensing receptor.[Ca2+]o-induced[Ca2+]i increase was inhibited byCa2+ channel inhibitors and appeared to be modulated byseveral kinase activities. [Ca2+]i increasewas potentiated by depletion of intracellular Ca2+ storesand depressed by inactivation of the Na+/Ca2+exchanger. The response to arginine vasopressin (AVP), which inducesinositol 1,4,5-trisphosphate-dependent[Ca2+]i increase in L6-C5 cells, was notmodified by high [Ca2+]o. On the contrary,AVP potentiated the [Ca2+]i increase in thepresence of elevated [Ca2+]o. Other clones ofthe L6 line as well as the rhabdomyosarcoma RD cell line and thesatellite cell-derived C2-C12 line expressed similar responses to high[Ca2+]o, and the amplitude of the responseswas correlated with the myogenic potential of the cells. 相似文献
16.
Denham M. Wisdom Gines M. Salido Lisa M. Baldwin Jaipaul Singh 《Molecular and cellular biochemistry》1996,154(2):123-132
This study investigates the effect of magnesium (Mg2+) on the secretory responses and the mobilization of calcium (Ca2+) and Mg2+ evoked by cholecystokinin-octapeptide (CCK-8) in the exocrine rat pancreas. In the isolated intact perfused pancreas CCK-8 (10–10 M) produced marked increases in juice flow and total protein output in zero and normal (1.1 mM) extracellular Mg2+ [Mg2+]o compared to a much reduced secretory response in elevated (5 mM and 10 mM) [Mg2+]o Similar effects of perturbation of [Mg2+]o on amylase secretion and 45Ca2+ uptake (influx) were obtained in isolated pancreatic segments. In pancreatic acinar cells loaded with the fluorescent bioprobe fura-2 acetomethylester (AM), CCK-8 evoked marked increases in cytosolic free Ca2+ concentration [Ca2+]i in zero and normal [Mg2+]o compared to a much reduced response in elevated [Mg2+]o Pretreatment of acinar cells with either dibutyryl cyclic AMP (DB2 cAMP) or forskolin had no effect on the CCK-8 induced changes in [Ca2+]i. In magfura-2-loaded acinar cells CCK-8 (10–8 M) stimulated an initial transient rise in intracellular free Mg2+ concentration [Mg2+]i followed by a more prolonged and sustained decrease. This response was abolished when sodium Na+ was replaced with N-methyl-D-glucamine (NMDG). Incubation of acinar cells with 10 mM Mg2+ resulted in an elevation in [Mg2+]i. Upon stimulation with CCK-8, [Mg2+]i. decreased only slightly compared with the response obtained in normal [Mg2+]o. CCK-8 caused a net efflux of Mg2+ in pancreatic segments; this effect was abolished when extracellular sodium [Na+]o was replaced with either NMDG or choline. The results indicate that Mg2+ can regulate CCK-8-evoked secretory responses in the exocrine pancreas possibly via Ca2+ mobilization. Moreover, the movement of Mg2+ in pancreatic acinar cells is dependent upon extracellular Na+. 相似文献
17.
HOFFMANN ROSANNE; TUFARIELLO JOANN; BISSON MARY A. 《Journal of experimental botany》1989,40(8):875-881
The effect of elevated Na+ concentration on Na+ permeability(PNa) and Na+ influx in the presence of two levels of externaldivalent cations was determined in Chara corallina and freshwater-culturedChara buckellii. When Na+ in the medium was increased from 1.0to 70 mol m3, Na+ influx increased in both species ifCa2+ was low (0.1 mol m3). If Ca2+ was increased to 7.0mol m3 when Na+ was increased, Na+ influx remained atthe low control level in C. corallina, and showed only a temporaryincrease in C. buckellii. Mg2+ was a better substitute for Ca2+in C. buckellii than in C. corallina. Na+ permeability data suggest that when the external Ca2+ concentrationis low, PNa does not increase in the presence of elevated NaCl;the increase in Na+ influx appears to be due to the increasein external Na+ concentration alone. Ca2 + supplementation appearsto decrease PNa whereas supplemental Mg2+ has no effect. Na+ effluxes were computed from previously determined net fluxesand the influxes. It was found that for both species, fluxesin both directions were stimulated in response to all experimentaltreatments, but Na+ influx always exceeded efflux. This resultedin net Na+ accumulation in the vacuoles of both species. The results are discussed with reference to net flux and electrophysiologicaldata obtained previously under identical conditions, as wellas the comparative salinity tolerance of both species and theNa+/divalent cation ratio. Key words: Na+ influx, Na+ tolerance, membrane potential, permeability, Chara 相似文献
18.
The influence of salt status of root tissue of Zea mays on influxof 84Rb and 22Na and net accumulation of K+ and Na+ was studied.Low-salt roots were grown in 0.5 mM CaCl2, and high-salt rootsin 2.5 mM KC1 + 7.5 mM NaCl + 0.5 mM CaCl2. High-salt statusgreatly reduced (approx. 90 per cent inhibition) both 22Na and86Rb influxes in the low concentration range isotherm (i.e.at external concentrations below 1 mM). A less marked inhibitionwas observed in the higher concentration range isotherm (130mM), indicating that the uptake in this range is less affectedby the salt status of the tissue. During transition from low- to high-salt status there was anet accumulation of K+ but not of Na+ despite the presence ofa measurable 22Na+ influx at all times. The presence of a continuous22Na influx but no net accumulation implies an Na+ efflux frommaize root tissue. The results differ significantly from thosepreviously published for barley and a possible explanation ofthese differences is discussed. 相似文献
19.
Slodzinski Martin K.; Blaustein Mordecai P. 《American journal of physiology. Cell physiology》1998,275(1):C251
Antisense oligodeoxynucleotides (AS-oligos) targeted to theNa+/Ca2+exchanger (NCX) inhibit NCX-mediatedCa2+ influx in mesenteric artery(MA) myocytes [Am. J. Physiol.269 (Cell Physiol. 38):C1340-C1345, 1995]. Here, we show AS-oligo knockdown ofNCX-mediated Ca2+ efflux. Ininitial experiments, the cytosolic freeCa2+ concentration([Ca2+]cyt)was raised, and sarcoplasmic reticulum (SR)Ca2+ sequestration was blockedwith caffeine and cyclopiazonic acid; the extracellularNa+-dependent (NCX) component ofCa2+ efflux was then selectivelyinhibited in AS-oligo-treated cells but not in controls (no oligos ornonsense oligos). In contrast, theLa3+-sensitive (plasmalemmaCa2+ pump) component ofCa2+ efflux was unaffected inAS-oligo-treated cells. Knockdown of NCX activity was reversed byincubating AS-oligo-treated cells in normal media for 5 days. Transient[Ca2+]cytelevations evoked by serotonin (5-HT) at 15-min intervals inAS-oligo-treated cells were indistinguishable from those in controls.When cells were stimulated every 3 min, however, the peak amplitudes ofthe second and third responses were larger, and[Ca2+]cytreturned to baseline more slowly, in AS-oligo-treated cells than incontrols. Peak 5-HT-evoked responses in the controls, but notAS-oligo-treated cells, were augmented more than twofold inNa+-free media. This implies thatNCX is involved in Na+ gradientmodulation of SR Ca2+ stores andcell responsiveness. The repetitive stimulation data suggest that theNCX may be important during tonic activation of arterial myocytes. 相似文献
20.
Mata A Marques D Martínez-Burgos MA Silveira J Marques J Mesquita MF Pariente JA Salido GM Singh J 《Molecular and cellular biochemistry》2008,307(1-2):193-207
This study investigated the effects of extracellular Mg2+ ([Mg2+]o) on basal and acetylcholine (ACh)-evoked amylase secretion and intracellular free Ca2+ ([Ca2+]i) in rat parotid acinar cells. In a medium containing 1.1 mM [Mg2+]o, ACh evoked significant increases in amylase secretion and [Ca2+]i. Either low (0 mM) or elevated (5 and 10 mM) [Mg2+]o attenuated ACh-evoked responses. In a nominally Ca2+ free medium, elevated [Mg2+]o attenuated basal and ACh-evoked amylase secretion and [Ca2+]i. In parotid acinar cells incubated with either 0, 1.1, 5 or 10 mM [Mg2+]o, ACh evoked a gradual decrease in [Mg2+]i. These results indicate that the ACh-evoked Mg2+ efflux is an active process since Mg2+ has to move against its gradient. Either lidocaine, amiloride, N-methyl-d-glucamine, quinidine, dinitrophenol or bumetanide can elevate [Mg2+]i above basal level. In the presence of these membrane transport inhibitors, ACh still evoked a decrease in [Mg2+]i but the response was less pronounced with either [Na+]o removal or in the presence of either amiloride or quinidine. These results indicate marked interactions between Ca2+ and Mg2+ signalling in parotid acinar cells and that ACh-evoked Mg2+ transport was not dependent upon [Na+]o. 相似文献