共查询到20条相似文献,搜索用时 31 毫秒
1.
Kuba M Higure Y Susaki H Hayato R Kuba K 《American journal of physiology. Cell physiology》2007,292(2):C896-C908
How the endoplasmic reticulum (ER) and mitochondria communicate with each other and how they regulate plasmalemmal Ca2+ entry were studied in cultured rat brown adipocytes. Cytoplasmic Ca2+ or Mg2+ and mitochondrial membrane potential were measured by fluorometry. The sustained component of rises in cytoplasmic Ca2+ concentration ([Ca2+]i) produced by thapsigargin was abolished by removing extracellular Ca2+, depressed by depleting extracellular Na+, and enhanced by raising extracellular pH. FCCP, dinitrophenol, and rotenone caused bi- or triphasic rises in [Ca2+]i, in which the first phase was accompanied by mitochondrial depolarization. The FCCP-induced first phase was partially inhibited by oligomycin but not by ruthenium red, cyclosporine A, U-73122, a Ca2+-free EGTA solution, and an Na+-free solution. The FCCP-induced second phase paralleling mitochondrial repolarization was partially blocked by removing extracellular Ca2+ and fully blocked by oligomycin but not by thapsigargin or an Na+-deficient solution, was accompanied by a rise in cytoplasmic Mg2+ concentration, and was summated with a high pH-induced rise in [Ca2+]i, whereas the extracellular Ca2+-independent component was blocked by U-73122 and cyclopiazonic acid. The FCCP-induced third phase was blocked by removing Ca2+ but not by thapsigargin, depressed by decreasing Na+, and enhanced by raising pH. Cyclopiazonic acid-evoked rises in [Ca2+]i in a Ca2+-free solution were depressed after FCCP actions. Thus mitochondrial uncoupling causes Ca2+ release, activating Ca2+ release from the ER and store-operated Ca2+ entry, and directly elicits a novel plasmalemmal Ca2+ entry, whereas Ca2+ release from the ER activates Ca2+ accumulation in, or release from, mitochondria, indicating bidirectional mitochondria-ER couplings in rat brown adipocytes. plasmalemmal calcium entry; calcium release; mitochondrial depolarization; FCCP 相似文献
2.
Kockskämper J Ahmmed GU Zima AV Sheehan KA Glitsch HG Blatter LA 《American journal of physiology. Cell physiology》2004,287(2):C527-C538
Palytoxin is a coral toxin that seriously impairs heart function, but its effects on excitation-contraction (E-C) coupling have remained elusive. Therefore, we studied the effects of palytoxin on mechanisms involved in atrial E-C coupling. In field-stimulated cat atrial myocytes, palytoxin caused elevation of diastolic intracellular Ca2+ concentration ([Ca2+]i), a decrease in [Ca2+]i transient amplitude, Ca2+ alternans followed by [Ca2+]i waves, and failures of Ca2+ release. The decrease in [Ca2+]i transient amplitude occurred despite high sarcoplasmic reticulum (SR) Ca2+ load. In voltage-clamped myocytes, palytoxin induced a current with a linear current-voltage relationship (reversal potential 5 mV) that was blocked by ouabain. Whole cell Ca2+ current and ryanodine receptor Ca2+ release channel function remained unaffected by the toxin. However, palytoxin significantly reduced Ca2+ pumping of isolated SR vesicles. In current-clamped myocytes stimulated at 1 Hz, palytoxin induced a depolarization of the resting membrane potential that was accompanied by delayed afterdepolarizations. No major changes of action potential configuration were observed. The results demonstrate that palytoxin interferes with the function of the sarcolemmal Na+-K+ pump and the SR Ca2+ pump. The suggested mode of palytoxin toxicity in the atrium involves the conversion of Na+-K+ pumps into nonselective cation channels as a primary event followed by depolarization, Na+ accumulation, and Ca2+ overload, which, in turn, causes arrhythmogenic [Ca2+]i waves and delayed afterdepolarizations. atrial myocytes; intracellular calcium 相似文献
3.
Store-operated Ca2+ entry modulates sarcoplasmic reticulum Ca2+ loading in neonatal rabbit cardiac ventricular myocytes 总被引:1,自引:0,他引:1
Huang J van Breemen C Kuo KH Hove-Madsen L Tibbits GF 《American journal of physiology. Cell physiology》2006,290(6):C1572-C1582
Store-operated Ca2+ entry (SOCE), which is Ca2+ entry triggered by the depletion of intracellular Ca2+ stores, has been observed in many cell types, but only recently has it been suggested to occur in cardiomyocytes. In the present study, we have demonstrated SOCE-dependent sarcoplasmic reticulum (SR) Ca2+ loading (loadSR) that was not altered by inhibition of L-type Ca2+ channels, reverse mode Na+/Ca2+ exchange (NCX), or nonselective cation channels. In contrast, lowering the extracellular [Ca2+] to 0 mM or adding either 0.5 mM Zn2+ or the putative store-operated channel (SOC) inhibitor SKF-96365 (100 µM) inhibited loadSR at rest. Interestingly, inhibition of forward mode NCX with 30 µM KB-R7943 stimulated SOCE significantly and resulted in enhanced loadSR. In addition, manipulation of the extracellular and intracellular Na+ concentrations further demonstrated the modulatory role of NCX in SOCE-mediated SR Ca2+ loading. Although there is little knowledge of SOCE in cardiomyocytes, the present results suggest that this mechanism, together with NCX, may play an important role in SR Ca2+ homeostasis. The data reported herein also imply the presence of microdomains unique to the neonatal cardiomyocyte. These findings may be of particular importance during open heart surgery in neonates, in which uncontrolled SOCE could lead to SR Ca2+ overload and arrhythmogenesis. cardiac ontogeny; cardiac excitation-contraction coupling; calcium homeostasis 相似文献
4.
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
5.
Mechanical strain-induced Ca(2+) waves are propagated via ATP release and purinergic receptor activation 总被引:3,自引:0,他引:3
Sauer H Hescheler J Wartenberg M 《American journal of physiology. Cell physiology》2000,279(2):C295-C307
Mechanical strainapplied to prostate cancer cells induced an intracellularCa2+ (Cai2+) wave spreading with avelocity of 15 µm/s. Cai2+ waves were notdependent on extracellular Ca2+ and membrane potentialbecause propagation was unaffected in high-K+ andCa2+-free solution. Waves did not depend on thecytoskeleton or gap junctions because cytochalasin B and nocodazole,which disrupt microfilaments and microtubules, respectively, and1-heptanol, which uncouples gap junctions, were without effects.Fluorescence recovery after photobleaching experiments revealed anabsence of gap junctional coupling. Cai2+ waveswere inhibited by the purinergic receptor antagonists basilen blue andsuramin; by pretreatment with ATP, UTP, ADP, UDP, 2-methylthio-ATP, andbenzoylbenzoyl-ATP; after depletion of ATP by 2-deoxyglucose; and afterATP scavenging by apyrase. Waves were abolished by the anion channelinhibitors 5-nitro-2-(3-phenylpropylamino)benzoic acid, tamoxifen,4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, niflumic acid, andgadolinium. ATP release following strain was significantly inhibited byanion channel blockers. Hence, ATP is secreted via mechanosensitiveanion channels and activates purinergic receptors on the same cell orneighboring cells in an autocrine and paracrine manner, thus leading toCai2+ wave propagation. 相似文献
6.
Role of Na+/Ca2+ exchange in regulating cytosolic Ca2+ in cultured human pulmonary artery smooth muscle cells 总被引:3,自引:0,他引:3
Zhang S Yuan JX Barrett KE Dong H 《American journal of physiology. Cell physiology》2005,288(2):C245-C252
A rise in cytosolic Ca2+ concentration ([Ca2+]cyt) in pulmonary artery smooth muscle cells (PASMC) is an important stimulus for cell contraction, migration, and proliferation. Depletion of intracellular Ca2+ stores opens store-operated Ca2+ channels (SOC) and causes Ca2+ entry. Transient receptor potential (TRP) cation channels that are permeable to Na+ and Ca2+ are believed to form functional SOC. Because sarcolemmal Na+/Ca2+ exchanger has also been implicated in regulating [Ca2+]cyt, this study was designed to test the hypothesis that the Na+/Ca2+ exchanger (NCX) in cultured human PASMC is functionally involved in regulating [Ca2+]cyt by contributing to store depletion-mediated Ca2+ entry. RT-PCR and Western blot analyses revealed mRNA and protein expression for NCX1 and NCKX3 in cultured human PASMC. Removal of extracellular Na+, which switches the Na+/Ca2+ exchanger from the forward (Ca2+ exit) to reverse (Ca2+ entry) mode, significantly increased [Ca2+]cyt, whereas inhibition of the Na+/Ca2+ exchanger with KB-R7943 (10 µM) markedly attenuated the increase in [Ca2+]cyt via the reverse mode of Na+/Ca2+ exchange. Store depletion also induced a rise in [Ca2+]cyt via the reverse mode of Na+/Ca2+ exchange. Removal of extracellular Na+ or inhibition of the Na+/Ca2+ exchanger with KB-R7943 attenuated the store depletion-mediated Ca2+ entry. Furthermore, treatment of human PASMC with KB-R7943 also inhibited cell proliferation in the presence of serum and growth factors. These results suggest that NCX is functionally expressed in cultured human PASMC, that Ca2+ entry via the reverse mode of Na+/Ca2+ exchange contributes to store depletion-mediated increase in [Ca2+]cyt, and that blockade of the Na+/Ca2+ exchanger in its reverse mode may serve as a potential therapeutic approach for treatment of pulmonary hypertension. sodium-calcium exchange; calcium homeostasis; vascular smooth muscle 相似文献
7.
Kurebayashi N Nishizawa H Nakazato Y Kurihara H Matsushita S Daida H Ogawa Y 《American journal of physiology. Cell physiology》2008,294(6):C1419-C1429
To investigate how intercellular coupling can be changed during Ca2+ overloading of ventricular muscle, we studied Ca2+ signals in individual cells and the histochemistry of the major gap junction channel, connexin43 (Cx43), using multicellular preparations. Papillary muscles were obtained from guinea pig ventricles and loaded with rhod-2. Sequential Ca2+ images of surface cells were obtained with a confocal microscope. In intact muscles, all cells showed simultaneous Ca2+ transients in response to field stimulation over a field of view of 0.3 x 0.3 mm2. In severely Ca2+-overloaded muscles, obtained by high-frequency stimulation in nonflowing Krebs solution, cells became less responsive to stimulation. Furthermore, nonsimultaneous but serial onsets of Ca2+ transients were often detected, suggesting a propagation delay of action potentials. The time lag of the onset between two aligned cells was sometimes as long as 100 ms. Similar lags were also observed in muscles with gap junction channels inhibited by heptanol. To investigate whether the phosphorylation state of Cx43 is affected in Ca2+-overloaded muscles, the distributions of phosphorylated and nonphosphorylated Cx43 were determined using specific antibodies. Most of the Cx43 was phosphorylated in the nonoverloaded muscles, whereas nonphosphorylated Cx43 was significantly elevated in severely Ca2+-overloaded muscles. Our results suggest that the propagation delay of action potential within a small area, a few square millimeters, can be a cause of abnormal conduction and a microreentry in Ca2+-overloaded heart. Inactivation of Na+ channels and inhibition of gap junctional communication may underlie the cell-to-cell propagation delay. Ca2+ transient; connexin43; propagation delay; gap junction; arrhythmia 相似文献
8.
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
9.
Three-dimensional simulation of calcium waves and contraction in cardiomyocytes using the finite element method 总被引:2,自引:0,他引:2
Okada J Sugiura S Nishimura S Hisada T 《American journal of physiology. Cell physiology》2005,288(3):C510-C522
To investigate the characteristics and underlying mechanisms of Ca2+ wave propagation, we developed a three-dimensional (3-D) simulator of cardiac myocytes, in which the sarcolemma, myofibril, and Z-line structure with Ca2+ release sites were modeled as separate structures using the finite element method. Similarly to previous studies, we assumed that Ca2+ diffusion from one release site to another and Ca2+-induced Ca2+ release were the basic mechanisms, but use of the finite element method enabled us to simulate not only the wave propagation in 3-D space but also the active shortening of the myocytes. Therefore, in addition to the dependence of the Ca2+ wave propagation velocity on the sarcoplasmic reticulum Ca2+ content and affinity of troponin C for Ca2+, we were able to evaluate the influence of active shortening on the propagation velocity. Furthermore, if the initial Ca2+ release took place in the proximity of the nucleus, spiral Ca2+ waves evolved and spread in a complex manner, suggesting that this phenomenon has the potential for arrhythmogenicity. The present 3-D simulator, with its ability to study the interaction between Ca2+ waves and contraction, will serve as a useful tool for studying the mechanism of this complex phenomenon. cardiac muscle cell; excitation-contraction coupling; mechanoelectrical feedback; spiral wave; arrhythmia 相似文献
10.
Pan Y Iwamoto T Uehara A Nakamura TY Imanaga I Shigekawa M 《American journal of physiology. Cell physiology》2000,279(2):C393-C402
Physiologicalfunctions of the intracellular regulatory domains of theNa+/Ca2+ exchanger NCX1 were studied byexamining Ca2+ handling in CCL39 cells expressing alow-affinity Ca2+ regulatory site mutant (D447V/D498I), anexchanger inhibitory peptide (XIP) region mutant displaying noNa+ inactivation (XIP-4YW), or a mutant lacking most of thecentral cytoplasmic loop (246-672). We found that D447V/D498Iwas unable to efficiently extrude Ca2+ from the cytoplasm,particularly during a small rise in intracellular Ca2+concentration induced by the physiological agonist -thrombin orthapsigargin. The same mutant took up Ca2+ much lessefficiently than the wild-type NCX1 in Na+-free medium whentransfectants were not loaded with Na+, although itappeared to take up Ca2+ normally in transfectantspreloaded with Na+. XIP-4YW and, to a lesser extent,246-672, but not NCX1 and D447V/D498I, markedly accelerated theloss of viability of Na+-loaded transfectants. Furthermore,XIP-4YW was not activated by phorbol ester, whereas XIP-4YW andD447V/D498I were resistant to inhibition by ATP depletion. The resultssuggest that these regulatory domains play important roles in thephysiological and pathological Ca2+ handling by NCX1, aswell as in the regulation of NCX1 by protein kinase C or ATP depletion. 相似文献
11.
Spatial and temporal mapping of pacemaker activity in interstitial cells of Cajal in mouse ileum in situ 总被引:5,自引:0,他引:5
Park KJ Hennig GW Lee HT Spencer NJ Ward SM Smith TK Sanders KM 《American journal of physiology. Cell physiology》2006,290(5):C1411-C1427
Spontaneous electrical pacemaker activity occurs in tunica muscularis of the gastrointestinal tract and drives phasic contractions. Interstitial cells of Cajal (ICC) are the pacemaker cells that generate and propagate electrical slow waves. We used Ca2+ imaging to visualize spontaneous rhythmicity in ICC in the myenteric region (ICC-MY) of the murine small intestine. ICC-MY, verified by colabeling with Kit antibody, displayed regular Ca2+ transients that occurred after electrical slow waves. ICC-MY formed networks, and Ca2+ transient wave fronts propagated through the ICC-MY networks at 2 mm/s and activated attached longitudinal muscle fibers. Nicardipine blocked Ca2+ transients in LM but had no visible effect on the transients in ICC-MY. -Glycyrrhetinic acid reduced the coherence of propagation, causing single cells to pace independently. Thus, virtually all ICC-MYs are spontaneously active, but normal activity is organized into propagating wave fronts. Inhibitors of dihydropyridine-resistant Ca2+ entry (Ni2+ and mibefradil) and elevated external K+ reduced the coherence and velocity of propagation, eventually blocking all activity. The mitochondrial uncouplers, FCCP, and antimycin and the inositol 1,4,5-trisphosphate receptor-inhibitory drug, 2-aminoethoxydiphenyl borate, abolished rhythmic Ca2+ transients in ICC-MY. These data show that global Ca2+ transients in ICC-MYs are a reporter of electrical slow waves in gastrointestinal muscles. Imaging of ICC networks provides a unique multicellular view of pacemaker activity. The activity of ICC-MY is driven by intracellular Ca2+ handling mechanisms and entrained by voltage-dependent Ca2+ entry and coupling of cells via gap junctions. Ca2+ signaling; slow waves; gastrointestinal motility 相似文献
12.
Differential regulation of Ca(2+) sparks and Ca(2+) waves by UTP in rat cerebral artery smooth muscle cells 总被引:6,自引:0,他引:6
Uridine 5'-triphosphate (UTP), a potent vasoconstrictor that activatesphospholipase C, shifted Ca2+ signaling from sparks towaves in the smooth muscle cells of rat cerebral arteries. UTPdecreased the frequency of Ca2+ sparks and transientCa2+-activated K+ (KCa) currentsand increased the frequency of Ca2+ waves. The UTP-inducedreduction in Ca2+ spark frequency did not reflect adecrease in global cytoplasmic Ca2+, Ca2+influx through voltage-dependent Ca2+ channels (VDCC), orCa2+ load of the sarcoplasmic reticulum (SR), since globalCa2+ was elevated, blocking VDCC did not prevent theeffect, and SR Ca2+ load did not decrease. However,blocking protein kinase C (PKC) with bisindolylmaleimide I did preventUTP reduction of Ca2+ sparks and transient KCacurrents. UTP decreased the effectiveness of caffeine, which increasesthe Ca2+ sensitivity of ryanodine-sensitiveCa2+ release (RyR) channels, to activate transientKCa currents. This work supports the concept thatvasoconstrictors shift Ca2+ signaling modalities fromCa2+ sparks to Ca2+ waves through the concertedactions of PKC on the Ca2+ sensitivity of RyR channels,which cause Ca2+ sparks, and of inositol trisphosphate(IP3) on IP3 receptors to generateCa2+ waves. 相似文献
13.
Xie Y Ottolia M John SA Chen JN Philipson KD 《American journal of physiology. Cell physiology》2008,295(2):C388-C393
The Na+/Ca2+ exchanger is the major Ca2+ extrusion mechanism in cardiac myocytes. The activity of the cardiac Na+/Ca2+ exchanger is dynamically regulated by intracellular Ca2+. Previous studies indicate that Ca2+ binding to a high-affinity Ca2+-binding domain (CBD1) in the large intracellular loop is involved in regulation. We generated transgenic zebrafish with cardiac-specific expression of CBD1 linked to yellow and cyan fluorescent protein. Ca2+ binding to CBD1 induces conformational changes, as detected by fluorescence resonance energy transfer. With this transgenic fish model, we were able to monitor conformational changes of the Ca2+ regulatory domain of Na+/Ca2+ exchanger in intact hearts. Treatment with the positive inotropic agents ouabain and isoproterenol increased both Ca2+ transients and Ca2+-induced changes in fluorescence resonance energy transfer. The results indicate that Ca2+ regulation of the Na+/Ca2+ exchanger domain CBD1 changes with inotropic state. The transgenic fish models will be useful to further characterize the regulatory properties of the Na+/Ca2+ exchanger in vivo. Ca2+-binding domain; sodium/calcium exchange; zebrafish; fluorescence resonance energy transfer 相似文献
14.
Characteristics of the Wave of Depolarization Induced by Wounding in Bidens pilosa L. 总被引:2,自引:0,他引:2
JULIEN J. L.; DESBIEZ M. O.; DE JAEGHER G.; FRACHISSE J. M. 《Journal of experimental botany》1991,42(1):131-137
Heating locally the hypocotyl of Bidens pilosa L. elicits awave of depolarization. The mechanism of the wave has been investigatedby means of microelectrophysiological techniques. The amplitudeof the transmembrane potential variation induced by an extracellularion concentration change (K+, Na+, Ca2+, Cl) was thesame in the resting conditions as during the slow wave. At pH4.0, the amplitude of the slow wave was reduced by 56% comparedwith the control performed at pH 7.0. In the presence of theuncoupler CCCP, the slow wave was not observed. The Ca2+ -chelatorEGTA and the Ca22+ -channel blocker La3+ reduced, respectively,the amplitude of the slow wave by 78% and 68%. These resultsindicate the involvement of Ca2+ in triggering the slow wave.A transient modification of the electrogenic H+ pump activity(inactivation-activation) and of the transmembrane H+ flux inthe slow wave are discussed. Key words: Slow wave (of depolarization), wounding, electrogenic pump, calcium, Bidens pilosa L 相似文献
15.
Chen L Lu XY Li J Fu JD Zhou ZN Yang HT 《American journal of physiology. Cell physiology》2006,290(4):C1221-C1229
We have previously demonstrated that intermittent high-altitude (IHA) hypoxia significantly attenuates ischemia-reperfusion (I/R) injury-induced excessive increase in resting intracellular Ca2+ concentrations ([Ca2+]i). Because the sarcoplasmic reticulum (SR) and Na+/Ca2+ exchanger (NCX) play crucial roles in regulating [Ca2+]i and both are dysfunctional during I/R, we tested the hypothesis that IHA hypoxia may prevent I/R-induced Ca2+ overload by maintaining Ca2+ homeostasis via SR and NCX mechanisms. We thus determined the dynamics of Ca2+ transients and cell shortening during preischemia and I/R injury in ventricular cardiomyocytes from normoxic and IHA hypoxic rats. IHA hypoxia did not affect the preischemic dynamics of Ca2+ transients and cell shortening, but it significantly suppressed the I/R-induced increase in resting [Ca2+]i levels and attenuated the depression of the Ca2+ transients and cell shortening during reperfusion. Moreover, IHA hypoxia significantly attenuated I/R-induced depression of the protein contents of SR Ca2+ release channels and/or ryanodine receptors (RyRs) and SR Ca2+ pump ATPase (SERCA2) and SR Ca2+ release and uptake. In addition, a delayed decay rate time constant of Ca2+ transients and cell shortening of Ca2+ transients observed during ischemia was accompanied by markedly inhibited NCX currents, which were prevented by IHA hypoxia. These findings indicate that IHA hypoxia may preserve Ca2+ homeostasis and contraction by preserving RyRs and SERCA2 proteins as well as NCX activity during I/R. intracellular Ca2+ concentration; Ca2+ transients; Ca2+ transporters; myofilament Ca2+ sensitivity 相似文献
16.
Huang J Hove-Madsen L Tibbits GF 《American journal of physiology. Cell physiology》2005,288(1):C195-C203
Much less is known about the contributions of the Na+/Ca2+ exchanger (NCX) and sarcoplasmic reticulum (SR) Ca2+ pump to cell relaxation in neonatal compared with adult mammalian ventricular myocytes. Based on both biochemical and molecular studies, there is evidence of a much higher density of NCX at birth that subsequently decreases during the next 2 wk of development. It has been hypothesized, therefore, that NCX plays a relatively more important role for cytosolic Ca2+ decline in neonates as well as, perhaps, a role in excitation-contraction coupling in reverse mode. We isolated neonatal ventricular myocytes from rabbits in four different age groups: 3, 6, 10, and 20 days of age. Using an amphotericin-perforated patch-clamp technique in fluo-3-loaded myocytes, we measured the caffeine-induced inward NCX current (INCX) and the Ca2+ transient. We found that the integral of INCX, an indicator of SR Ca2+ content, was greatest in myocytes from younger age groups when normalized by cell surface area and that it decreased with age. The velocity of Ca2+ extrusion by NCX (VNCX) was linear with [Ca2+] and did not indicate saturation kinetics until [Ca2+] reached 13 µM for each age group. There was a significantly greater time delay between the peaks of INCX and the Ca2+ transient in myocytes from the youngest age groups. This observation could be related to structural differences in the subsarcolemmal microdomains as a function of age. ontogeny of cardiac excitation-contraction coupling; sodium/calcium exchanger; cytosolic calcium concentration; subsarcolemmal calcium concentration; sarcoplasmic reticulum calcium content 相似文献
17.
The effects of a new, potent, and selective inhibitor of the Na+/Ca2+ exchange, SEA-0400 (SEA), on steady-state outward (forward exchange), inward (reverse exchange), and Ca2+/Ca2+ transport exchange modes were studied in internally dialyzed squid giant axons from both the extra- and intracellular sides. Inhibition by SEA takes place preferentially from the intracellular side of the membrane. Its inhibition has the following characteristics: it increases synergic intracellular Na+ (Nai+) + intracellular H+ (Hi+) inactivation, is antagonized by ATP and intracellular alkalinization, and is enhanced by intracellular acidification even in the absence of Na+. Inhibition by SEA is still present even after 1 h of its removal from the experimental solutions, whereas removal of the cointeracting agents of inhibition, Nai+ and Hi+, even in the continuous presence of SEA, releases inhibition, indicating that SEA facilitates the reversible attachment of the natural Hi+ and Nai+ synergic inhibitors. On the basis of a recent model of squid Na+/Ca2+ exchange regulation (DiPolo R and Beaugé L. J Physiol 539: 791803, 2002), we suggest that SEA acts on the Hi+ + Nai+ inactivation process and can interact with the Na+-free and Na+-bound protonized carrier. Protection by ATP concurs with the antagonism of the nucleotide by Hi+ + Nai+ synergic inhibition. ionic-metabolic interactions 相似文献
18.
Of the many ongoing controversies regarding the workings of the sarcoplasmic reticulum (SR) in cardiac myocytes, two unresolved and interconnected topics are 1), mechanisms of calcium (Ca2+) wave propagation, and 2), speed of Ca2+ diffusion within the SR. Ca2+ waves are initiated when a spontaneous local SR Ca2+ release event triggers additional release from neighboring clusters of SR release channels (ryanodine receptors (RyRs)). A lack of consensus regarding the effective Ca2+ diffusion constant in the SR (DCa,SR) severely complicates our understanding of whether dynamic local changes in SR [Ca2+] can influence wave propagation. To address this problem, we have implemented a computational model of cytosolic and SR [Ca2+] during Ca2+ waves. Simulations have investigated how dynamic local changes in SR [Ca2+] are influenced by 1), DCa,SR; 2), the distance between RyR clusters; 3), partial inhibition or stimulation of SR Ca2+ pumps; 4), SR Ca2+ pump dependence on cytosolic [Ca2+]; and 5), the rate of transfer between network and junctional SR. Of these factors, DCa,SR is the primary determinant of how release from one RyR cluster alters SR [Ca2+] in nearby regions. Specifically, our results show that local increases in SR [Ca2+] ahead of the wave can potentially facilitate Ca2+ wave propagation, but only if SR diffusion is relatively slow. These simulations help to delineate what changes in [Ca2+] are possible during SR Ca2+release, and they broaden our understanding of the regulatory role played by dynamic changes in [Ca2+]SR. 相似文献
19.
The cytoplasmic pH undergoes a biphasic change when neutrophils are activated. The role of Ca2+ in initiating these changes was investigated. No correlation was found between the increased cytosolic [Ca2+] and the stimulation of the Na+/H+ antiport. Similarly, the cytoplasmic acidification elicited by activation in Na+-free media was found to be unrelated to [Ca2+]. Reversal of Na+/H+ exchange was also ruled out as the source of the acidification. Data using a variety of soluble activators indicate that metabolic acid generation is largely responsible for the observed drop in cytoplasmic pH. 相似文献
20.
Nakamura Yoshiyuki; Kasamo Kunihiro; Sakata Makato; Ohta Eiji 《Plant & cell physiology》1992,33(2):139-149
Extrusion of protons as a response to high-NaCl stress in intactmung bean roots was investigated at different external concentrationsof Ca2+ ions ([Ca2+]ex). The extrusion of protons was graduallyenhanced in the roots exposed to 100 mM NaCl, and high [Ca2+]exdiminished this enhancement of the extrusion. Vesicles of plasmalemmaand tonoplast were prepared from the roots and the H+-translocatingATPase (H+-ATPase) activities associated with the two typesof membrane and the H+-pyrophosphatase (H+-PPase) activity ofthe tonoplast were assayed. The plasmalemma ATPase was stimulatedin parallel with dramatic increases in the intracellular concentrationof Na+([Na+]in). High [Ca2+]ex prevented the increase in [Na+]inand diminished the stimulation of ATPase activity. The tonoplastATPase showed a rapid response to salt stress and was similarlystimulated even at high [Ca2+]M. The activities of both ATPaseswere, however, insensitive to concentrations of Na+ ions upto 100 HIM. By contrast, H+-PPase activity of the tonoplastwas severely inhibited with increasing [Na+]in under salt stressand recovered with high [Ca2+]ex. These findings suggest thathigh-NaCl stress increases the intracellular concentration ofNa+ ions in mung bean roots, which inhibits the tonoplast H+-PPase,and the activity of the plasmalemma H+-ATPase is thereby stimulatedand regulates the cytoplasmic pH. (Received March 26, 1991; Accepted December 13, 1991) 相似文献