共查询到20条相似文献,搜索用时 15 毫秒
1.
Norepinephrine-induced Ca2+ waves depend on InsP3 and ryanodine receptor activation in vascular myocytes 总被引:1,自引:0,他引:1
Boittin Francois-Xavier; Macrez Nathalie; Halet Guillaume; Mironneau Jean 《American journal of physiology. Cell physiology》1999,277(1):C139
In rat portal veinmyocytes, Ca2+ signals can begenerated by inositol 1,4,5-trisphosphate(InsP3)- and ryanodine-sensitive Ca2+ release channels, which arelocated on the same intracellular store. Using a laser scanningconfocal microscope associated with the patch-clamp technique, weshowed that propagated Ca2+ wavesevoked by norepinephrine (in the continuous presence of oxodipine) werecompletely blocked after internal application of ananti-InsP3 receptor antibody.These propagated Ca2+ waves werealso reduced by ~50% and transformed in homogenous Ca2+ responses after applicationof an anti-ryanodine receptor antibody or ryanodine. All-or-noneCa2+ waves obtained withincreasing concentrations of norepinephrine were transformed in adose-response relationship with a Hill coefficient close to unity afterryanodine receptor inhibition. Similar effects of the ryanodinereceptor inhibition were observed on the norepinephrine- andACh-induced Ca2+ responses innon-voltage-clamped portal vein and duodenal myocytes and on thenorepinephrine-induced contraction. Taken together, these results showthat ryanodine-sensitive Ca2+release channels are responsible for the fast propagation of Ca2+ responses evoked by variousneurotransmitters producing InsP3 in vascular and visceral myocytes. 相似文献
2.
Kurebayashi N Yamashita H Nakazato Y Daida H Ogawa Y 《American journal of physiology. Cell physiology》2004,287(6):C1646-C1656
Ca+ waves have been implicated in Ca2+ overload-induced cardiac arrhythmias. To deepen understanding of the behavior of Ca2+ waves in a multicellular system, consecutive two-dimensional Ca2+ images were obtained with a confocal microscope from surface cells of guinea pig ventricular papillary muscles loaded with fluo 3 or rhod 2. In intact muscles, no Ca2+ waves were detected under the resting condition, whereas they were frequently observed during the rest immediately after high-frequency stimulations where cytoplasmic Ca2+ concentration and Ca2+ stored in the sarcoplasmic reticulum (SR) were gradually decreasing. The intervals of Ca2+ waves increased as they occurred later, their amplitudes and velocities remaining unchanged. A SERCA inhibitor reversibly prolonged the wave intervals. In Na+-free/Ca2+-free medium where neither Ca2+ influx nor Na+/Ca2+ exchange took place, recurrent Ca2+ waves emerged at constant intervals in each cell. These results are consistent with the conclusion that the loading level of the SR is critical for induction of Ca2+ waves. Each cell independently exhibited its own regular rhythm of Ca2+ wave with a distinct interval. These waves propagated in either direction along the longitudinal axis within a muscle cell, but seldom beyond the cell boundary. In contrast, in partially damaged muscles that showed spontaneous Ca2+ waves at rest in normal Krebs solution, their propagation often was unidirectional, decreasing in frequency. In these cases, however, Ca2+ waves rarely moved beyond the cellular boundary. The gradient of the cytoplasmic Ca2+ concentration was suggested to be the cause of the one-way propagation. wave propagation; luminal calcium ion; cytoplasmic calcium ion; sodium/calcium exchange 相似文献
3.
Pfeiffer Fatima; Sternfeld Lutz; Schmid Andreas; Schulz Irene 《American journal of physiology. Cell physiology》1998,274(3):C663
We haveinvestigated control mechanisms involved in the propagation ofagonist-induced Ca2+ waves inisolated mouse pancreatic acinar cells. Using a confocal laser-scanningmicroscope, we were able to show that maximal stimulation of cells withacetylcholine (ACh, 500 nM) or bombesin (1 nM) caused an initialCa2+ release of comparable amountswith both agonists at the luminal cell pole. SubsequentCa2+ spreading to the basolateralmembrane was faster with ACh (17.3 ± 5.4 µm/s) than with bombesin(8.0 ± 2.2 µm/s). The speed of bombesin-inducedCa2+ waves could be increased upto the speed of ACh-induced Ca2+waves by inhibition of protein kinase C (PKC). Activation of PKCsignificantly decreased the speed of ACh-inducedCa2+ waves but had only littleeffect on bombesin-evoked Ca2+waves. Within 3 s after stimulation, production of inositol1,4,5-trisphosphate [Ins(1,4,5)P3]was higher in the presence of ACh compared with bombesin, whereasbombesin induced higher levels of diacylglycerol (DAG) than ACh. Thesedata suggest that the slower propagation speed of bombesin-inducedCa2+ waves is due to higheractivation of PKC in the presence of bombesin compared with ACh. Thehigher increase in bombesin- compared with ACh-induced DAG productionis probably due to activation of phospholipase D (PLD). Inhibition ofthe PLD-dependent DAG production by preincubation with 0.3% butanolled to an acceleration of the bombesin-induced Ca2+ wave. In further experiments,we could show that ruthenium red (100 µM), an inhibitor ofCa2+-inducedCa2+ release in skeletal muscle,also decreased the speed of ACh-induced Ca2+ waves. The effect ofruthenium red was not additive to the effect of PKC activation. Fromthe data, we conclude that, following Ins(1,4,5)P3-inducedCa2+ release in the luminal cellpole, secondary Ca2+ release fromstores, which are located in series between the luminal and the basalplasma membrane, modifies Ca2+spreading toward the basolateral cell side byCa2+-inducedCa2+ release. Activation of PKCleads to a reduction in Ca2+release from these stores and therefore could explain the slower propagation of Ca2+ waves in thepresence of bombesin compared with ACh. 相似文献
4.
Takagishi Y Yasui K Severs NJ Murata Y 《American journal of physiology. Cell physiology》2000,279(6):C1963-C1969
Ca2+influx via sarcolemmal voltage-dependent Ca2+ channels(L-type Ca2+ channels) is the fundamental step inexcitation-contraction (E-C) coupling in cardiac myocytes.Physiological and pharmacological studies reveal species-specificdifferences in E-C coupling resulting from a difference in thecontribution of Ca2+ influx and intracellularCa2+ release to activation of contraction. We investigatedthe distribution of L-type Ca2+ channels in isolatedcardiac myocytes from rabbit and rat ventricle by correlativeimmunoconfocal and immunogold electron microscopy. Immunofluorescence labeling revealed discrete spots in the surface plasma membrane and transverse (T) tubules in rabbit myocytes. In ratmyocytes, labeling appeared more intense in T tubules than in thesurface sarcolemma. Immunogold electron microscopy extended thesefindings, showing that the number of gold particles in the surfaceplasma membrane was significantly higher in rabbit than rat myocytes.In rabbit myocyte plasma membrane, the gold particles were distributedas clusters in both regions that were associated with junctionalsarcoplasmic reticulum and those that were not. The findings areconsistent with the idea that influx of Ca2+ via surfacesarcolemmal Ca2+ channels contributes to intracellularCa2+ to a greater degree in rabbit than in rat myocytes. 相似文献
5.
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
6.
Lemon G 《Bulletin of mathematical biology》2004,66(1):65-90
The propagation of fire-diffuse-fire Ca2+ waves through a three-dimensional rectangular domain is considered. The domain is infinite in extent in the direction of propagation but with lateral barriers to diffusion which contain Ca2+ pumps. The Ca2+ concentration profile due to the firing of a release site (spark) is derived analytically based on the Green’s function for the diffusion equation on the domain. The existence, stability and speed of these waves is shown to be critically dependent on the dimensions of the domain and the Ca2+ pump rate. It is shown that the smaller the dimensions of the region, the lower the Ca2+ release flux required for wave propagation, and the higher the wave speed. Also it is shown that the region may support multiple Ca2+ wavefronts of varying wave speed. This model is relevant to subsarcolemmal waves in atrial myocytes (Kockskämper et al., 2001, Biophys. J. 81, 2590–2605), and the results may be of importance in understanding the roles of the endoplasmic/sarcoplasmic reticulum, surface membranes and Ca2+ pumps in the intracellular Ca2+ dynamics of cells. 相似文献
7.
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
8.
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
9.
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
10.
The subcellular spatial and temporal organization ofagonist-induced Ca2+ signals wasinvestigated in single cultured vascular endothelial cells.Extracellular application of ATP initiated a rapid increase ofintracellular Ca2+ concentration([Ca2+]i)in peripheral cytoplasmic processes from where activation propagated asa[Ca2+]iwave toward the central regions of the cell. The average propagation velocity of the[Ca2+]iwave in the peripheral processes was 20-60 µm/s, whereas in thecentral region the wave propagated at <10 µm/s. The time course ofthe recovery of[Ca2+]idepended on the cell geometry. In the peripheral processes (i.e.,regions with a high surface-to-volume ratio)[Ca2+]ideclined monotonically, whereas in the central region[Ca2+]idecreased in an oscillatory fashion. Propagating[Ca2+]iwaves were preceded by small, highly localized[Ca2+]itransients originating from 1- to 3-µm-wide regions. The average amplitude of these elementary events ofCa2+ release was 23 nM, and theunderlying flux of Ca2+ amountedto ~1-2 × 1018mol/s or ~0.3 pA, consistent with aCa2+ flux through a single orsmall number of endoplasmic reticulum Ca2+-release channels. 相似文献
11.
Sergey V. Yagodin Lynne Holtzclaw Carol A. Sheppard James T. Russell 《Developmental neurobiology》1994,25(3):265-280
In astrocytes in primary culture, activation of neurotransmitter receptors results in intracellular calcium signals that propagate as waves across the cell. Similar agonist-induced calcium waves have been observed in astrocytes in organotypic cultures in response to synaptic activation. By using primary cultured astrocytes grown on glass coverslips, in conjunction with fluorescence microscopy we have analyzed agonist-induced Ca2+ wave initiation and propagation in individual cells. Both norepinephrine and glutamate elicited Ca2+ signals which were initiated focally and discretely in one region of the cell, from where the signals spread as waves along the entire length of the cell. Analysis of the wave propagation and the waveform revealed that the propagation was nonlinear with one or more focal loci in the cytoplasm where the wave was regeneratively amplified. These individual loci appear as discrete focal areas 7–15 μm in diameter and having intrinsic oscillatory properties that differ from each other. The wave initiation locus and the different amplification loci remained invariant in space during the course of the experiment and supported an identical spatiotemporal pattern of signalling in any given cell in response to multiple agonist applications and when stimulated with different agonists which are coupled via InsP3. Cytoplasmic Ca2+ concentration at rest was consistently higher (17 ± 4nM, mean ± S.E.M.) in the wave initiation locus compared with the rest of the cytoplam. The nonlinear propagation results from significant changes in signal rise times, amplitudes, and wave velocity in cellular regions of active loci. Analysis of serial slices across the cell revealed that the rise times and amplitudes of local signals were as much as three- to fourfold higher in the loci of amplification. A phenomenon of hierarchy in local amplitudes of the signal in the amplification loci was observed with the wave initiation locus having the smallest and the most distal locus having largest amplitude. By this mechanism locally very high concentrations of Ca2+ are achieved in strategic locations in the cell in response to receptor activation. While the average wave velocity calculated over the length of the cell was 10–15 μm/s, in the active loci rates as high as 40 μm/s were measured. Wave velocity was fivefold lower in regions of the cell separating active loci. The differences in the intrinsic oscillatory periods give rise to local Ca2+ waves that show the properties of collision and annihilation. It is hypothesized that the wave front provokes regenerative Ca2+ release from specialized areas in the cell where the endoplasmic reticulum is endowed with higher density of InsP3 receptor channels. Thus wave propagation is achieved by a process of diffusion and regenerative Ca2+ release in multiple cellular loci provoked by the advancing wave front; in this way, wave propagation is nonlinear and saltatory. Regenerative Ca2+ wave propagation from distal atrocytic processes to the cell body and neighboring cells is likely to provide an important signalling mechanism in the nervous system. 1994 John Wiley & Sons, Inc. 相似文献
12.
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
13.
Copello JA Zima AV Diaz-Sylvester PL Fill M Blatter LA 《American journal of physiology. Cell physiology》2007,292(6):C2129-C2140
During the cardiac action potential, Ca2+ entry through dyhidropyridine receptor L-type Ca2+ channels (DHPRs) activates ryanodine receptors (RyRs) Ca2+-release channels, resulting in massive Ca2+ mobilization from the sarcoplasmic reticulum (SR). This global Ca2+ release arises from spatiotemporal summation of many localized elementary Ca2+-release events, Ca2+ sparks. We tested whether DHPRs modulate Ca2+sparks in a Ca2+ entry-independent manner. Negative modulation by DHPR of RyRs via physical interactions is accepted in resting skeletal muscle but remains controversial in the heart. Ca2+ sparks were studied in cat cardiac myocytes permeabilized with saponin or internally perfused via a patch pipette. Bathing and pipette solutions contained low Ca2+ (100 nM). Under these conditions, Ca2+ sparks were detected with a stable frequency of 3–5 sparks·s–1·100 µm–1. The DHPR blockers nifedipine, nimodipine, FS-2, and calciseptine decreased spark frequency, whereas the DHPR agonists Bay-K8644 and FPL-64176 increased it. None of these agents altered the spatiotemporal characteristics of Ca2+ sparks. The DHPR modulators were also without effect on SR Ca2+ load (caffeine-induced Ca2+ transients) or sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) activity (Ca2+ loading rates of isolated SR microsomes) and did not change cardiac RyR channel gating (planar lipid bilayer experiments). In summary, DHPR modulators affected spark frequency in the absence of DHPR-mediated Ca2+ entry. This action could not be attributed to a direct action of DHPR modulators on SERCA or RyRs. Our results suggest that the activity of RyR Ca2+-release units in ventricular myocytes is modulated by Ca2+ entry-independent conformational changes in neighboring DHPRs. exitation-contraction coupling; ryanodine receptor; sarco(endo)plasmic reticulum Ca2+-ATPase; dihydropyridine receptor; sarcoplasmic reticulum 相似文献
14.
Intercellular Ca2+ waves can coordinate the action of large numbers of cells over significant distances. Recent work in many different systems
has indicated that the release of ATP is fundamental for the propagation of most Ca2+ waves. In the organ of hearing, the cochlea, ATP release is involved in critical signalling events during tissue maturation.
ATP-dependent signalling is also implicated in the normal hearing process and in sensing cochlear damage. Here, we show that
two distinct Ca2+ waves are triggered during damage to cochlear explants. Both Ca2+ waves are elicited by extracellular ATP acting on P2 receptors, but they differ in their source of Ca2+, their velocity, their extent of spread and the cell type through which they propagate. A slower Ca2+ wave (14 μm/s) communicates between Deiters’ cells and is mediated by P2Y receptors and Ca2+ release from IP3-sensitive stores. In contrast, a faster Ca2+ wave (41 μm/s) propagates through sensory hair cells and is mediated by Ca2+ influx from the external environment. Using inhibitors and selective agonists of P2 receptors, we suggest that the faster
Ca2+ wave is mediated by P2X4 receptors. Thus, in complex tissues, the expression of different receptors determines the propagation of distinct intercellular
communication signals. 相似文献
15.
Activation of calcium release assessed by calcium release-induced inactivation of calcium current in rat cardiac myocytes 总被引:4,自引:0,他引:4
Zahradníková A Kubalová Z Pavelková J Györke S Zahradník I 《American journal of physiology. Cell physiology》2004,286(2):C330-C341
In mammalian cardiac myocytes, calcium released into the dyadic space rapidly inactivates calcium current (ICa). We used this Ca2+ release-dependent inactivation (RDI) of ICa as a local probe of sarcoplasmic reticulum Ca2+ release activation. In whole cell patch-clamped rat ventricular myocytes, Ca2+ entry induced by short prepulses from 50 mV to positive voltages caused suppression of peak ICa during a test pulse. The negative correlation between peak ICa suppression and ICa inactivation during the test pulse indicated that RDI evoked by the prepulse affected only calcium channels in those dyads in which calcium release was activated. Ca2+ ions injected during the prepulse and during the subsequent tail current suppressed peak ICa in the test pulse to a different extent. Quantitative analysis indicated that equal Ca2+ charge was 3.5 times less effective in inducing release when entering during the prepulse than when entering during the tail. Tail Ca2+ charge injected by the first voltage-dependent calcium channel (DHPR) openings was three times less effective than that injected by DHPR reopenings. These findings suggest that calcium release activation can be profoundly influenced by the recent history of L-type Ca2+ channel activity due to potentiation of ryanodine receptors (RyRs) by previous calcium influx. This conclusion was confirmed at the level of single RyRs in planar lipid bilayers: using flash photolysis of the calcium cage NP-EGTA to generate two sequential calcium stimuli, we showed that RyR activation in response to the second stimulus was four times higher than that in response to the first stimulus. excitation-contraction coupling 相似文献
16.
New insights into the molecular and cellular workings of the cardiac Na+/Ca2+ exchanger 总被引:3,自引:0,他引:3
Hilgemann DW 《American journal of physiology. Cell physiology》2004,287(5):C1167-C1172
The cardiac Na+/Ca2+ exchanger (NCX1) is almost certainly the major Ca2+ extrusion mechanism in cardiac myocytes, although the driving force for Ca2+ extrusion is quite small. To explain multiple recent results, it is useful to think of the exchanger as a slow Ca2+ buffer that can reverse its function multiple times during the excitation-contraction cycle (ECC). An article by the group of John Reeves brings new insights to this function by analyzing the role of regulatory domains of NCX1 that mediate its activation by a rise of cytoplasmic Ca2+. It was demonstrated that the gating reactions are operative just in the physiological range of Ca2+ changes, a few fold above resting Ca2+ level, and that they prevent the exchanger from damping out the influence of mechanisms that transiently increase Ca2+ levels. Furthermore, exchangers with deleted regulatory domains are shown to reduce resting Ca2+ to lower levels than achieved by wild-type exchangers. A study by the group of Kenneth Philipson demonstrated that the NCX1 regulatory domain can bind and respond to Ca2+ changes on the time scale of the ECC in rat myocytes. At the same time, studies of transgenic mice and NCX1 knockout mice generated by the Philipson group revealed that large changes of NCX1 activity have rather modest effects on ECC. Simple simulations predict these results very well: murine cardiac ECC is very sensitive to small changes of the Na+ gradient, very sensitive to changes of the sarcoplasmic reticulum Ca2+ pump activity, and very insensitive to changes of NCX1 activity. It is speculated that the NCX1 gating reactions not only regulate coupled 3Na+:1Ca2+ exchange but also control the exchangers Na+ leak function that generates background Na+ influx and depolarizing current in cardiac myocytes. excitation-contraction cycle 相似文献
17.
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
18.
Regulation of dynamic behavior of cardiac ryanodine receptor by Mg2+ under simulated physiological conditions 总被引:1,自引:0,他引:1
Zahradníková A Dura M Györke I Escobar AL Zahradník I Györke S 《American journal of physiology. Cell physiology》2003,285(5):C1059-C1070
Mg2+, an important constituent of the intracellular milieu in cardiac myocytes, is known to inhibit ryanodine receptor (RyR) Ca2+ release channels by competing with Ca2+ at the cytosolic activation sites of the channel. However, the significance of this competition for local, dynamic Ca2+-signaling processes thought to govern cardiac excitation-contraction (EC) coupling remains largely unknown. In the present study, Ca2+ stimuli of different waveforms (i.e., sustained and brief) were generated by photolysis of the caged Ca2+ compound nitrophenyl (NP)-EGTA. The evoked RyR activity was measured in planar lipid bilayers in the presence of 0.6-1.3 mM free Mg2+ at the background of 3 mM total ATP in the presence or absence of 1 mM luminal Ca2+. Mg2+ dramatically slowed the rate of activation of RyRs in response to sustained (=" BORDER="0">10-ms) elevations in Ca2+ concentration. Paradoxically, Mg2+ had no measurable impact on the kinetics of the RyR response induced by physiologically relevant, brief (<1-ms) Ca2+ stimuli. Instead, the changes in activation rate observed with sustained stimuli were translated into a drastic reduction in the probability of responses. Luminal Ca2+ did not affect the peak open probability or the probability of responses to brief Ca2+ signals; however, it slowed the transition to steady state and increased the steady-state open probability of the channel. Our results indicate that Mg2+ is a critical physiological determinant of the dynamic behavior of the RyR channel, which is expected to profoundly influence the fidelity of coupling between L-type Ca2+ channels and RyRs in heart cells. excitation-contraction coupling; cardiac myocytes; magnesium; calcium signaling 相似文献
19.
This study investigated the mechanisms underlying the propagation of cytoplasmic calcium waves and the genesis of systolic Ca2+ alternans in cardiac myocytes lacking transverse tubules (t-tubules). These correspond to atrial cells of either small mammals or large mammals that have lost their t-tubules due to disease-induced structural remodeling (e.g., atrial fibrillation). A mathematical model was developed for a cluster of ryanodine receptors distributed on the cross section of a cell that was divided into 13 elements with a spatial resolution of 2 μm. Due to the absence of t-tubules, L-type Ca2+ channels were only located in the peripheral elements close to the cell-membrane surface and produced Ca2+ signals that propagated toward central elements by triggering successive Ca2+-induced Ca2+ release (CICR) via Ca2+ diffusion between adjacent elements. Under control conditions, the Ca2+ signals did not fully propagate to the central region of the cell. However, with modulation of several factors responsible for Ca2+ handling, such as the L-type Ca2+ channels (Ca2+ influx), SERCA pumps (sarcoplasmic reticulum (SR) Ca2+ uptake), and ryanodine receptors (SR Ca2+ release), Ca2+ wave propagation to the center of the cell could occur. These simulation results are consistent with previous experimental data from atrial cells of small mammals. The model further reveals that spatially functional heterogeneity in Ca2+ diffusion within the cell produced a steep relationship between the SR Ca2+ content and the cytoplasmic Ca2+ concentration. This played an important role in the genesis of Ca2+ alternans that were more obvious in central than in peripheral elements. Possible association between the occurrence of Ca2+ alternans and the model parameters of Ca2+ handling was comprehensively explored in a wide range of one- and two-parameter spaces. In addition, the model revealed a spontaneous second Ca2+ release in response to a single voltage stimulus pulse with SR Ca2+ overloading and augmented Ca2+ influx. This study provides what to our knowledge are new insights into the genesis of Ca2+ alternans and spontaneous second Ca2+ release in cardiac myocytes that lack t-tubules. 相似文献
20.
Punctate releases of Ca2+, called Ca2+ sparks, originate at the regular array of t-tubules in cardiac myocytes and skeletal muscle. During Ca2+ overload sparks serve as sites for the initiation and propagation of Ca2+ waves in myocytes. Computer simulations of spark-mediated waves are performed with model release sites that reproduce the adaptive Ca2+ release observed for the ryanodine receptor. The speed of these waves is proportional to the diffusion constant of Ca2+, D, rather than D, as is true for reaction-diffusion equations in a continuous excitable medium. A simplified "fire-diffuse-fire" model that mimics the properties of Ca2+-induced Ca2+ release (CICR) from isolated sites is used to explain this saltatory mode of wave propagation. Saltatory and continuous wave propagation can be differentiated by the temperature and Ca2+ buffer dependence of wave speed. 相似文献