Satoh H, Blatter L A, Bers D M
Department of Physiology, Loyola University Chicago, Maywood, Illinois 60153, USA.
Am J Physiol. 1997 Feb;272(2 Pt 2):H657-68. doi: 10.1152/ajpheart.1997.272.2.H657.
In heart, spontaneous local increases in cytosolic Ca2+ concentration ([Ca2+]i) called "Ca2+ sparks" may be fundamental events underlying both excitation-contraction coupling and resting Ca2+ leak from the sarcoplasmic reticulum (SR). In this study, resting Ca2+ sparks were analyzed in rabbit and rat ventricular myocytes with laser scanning confocal microscopy and the fluorescent Ca2+ indicator fluo 3. During the first 20 s of rest after regular electrical stimulation, both the frequency of Ca2+ sparks and SR Ca2+ content gradually decreased in rabbit. When rabbit SR Ca2+ content was decreased by reduction of stimulation rate. the initial resting spark frequency was also decreased, even though resting [Ca2+]i was unchanged. The rest-dependent decrease in spark frequency in rabbit cells was prevented by inhibition of Na+/Ca2+ exchange (which also prevents SR Ca2+ depletion during rest). These results suggest that elevation of SR Ca2+ content can increase Ca2+ spark frequency. In contrast to rabbit cells, 20 s of rest produced a gradual increase in spark frequency in rat cells, although SR Ca2+ content was constant and Ca2+ influx was completely prevented. This indicates that there is a time-dependent increase in spark probability during rest that is independent of [Ca2+]i or SR Ca2+. This effect was also apparent in rabbit cells when SR Ca2+ depletion was prevented by blocking Na+/Ca2+ exchange. Stimulation of Ca2+ extrusion via Na+/Ca2+ exchange in the rat (by Ca2+-free superfusion, which slowly depletes SR Ca2+ content) converted the normal rest-dependent increase in spark frequency to a decrease. The amplitude of individual Ca2+ sparks increased with increasing SR Ca2+ content. In the Ca2+-overloaded state, fusion of sparks or long-lasting localized increases of [Ca2+]i were observed with increased spark frequency. We conclude that the resting frequency of Ca2+ sparks can be independently affected by changes in SR Ca2+ content, [Ca2+]i, or rest period. The latter may reflect recovery of the SR Ca2+ release channels from inactivation or adaptation.
在心脏中，被称为“钙火花”的胞质钙浓度（[Ca2+]i）的自发性局部升高可能是兴奋-收缩偶联和肌浆网（SR）静息钙泄漏的基本事件。在本研究中，使用激光扫描共聚焦显微镜和荧光钙指示剂fluo 3对兔和大鼠心室肌细胞中的静息钙火花进行了分析。在常规电刺激后的最初20秒静息期内，兔心肌细胞中钙火花的频率和SR钙含量均逐渐降低。当通过降低刺激频率使兔SR钙含量降低时，尽管静息[Ca2+]i不变，但初始静息火花频率也降低。抑制钠/钙交换（这也可防止静息期SR钙耗竭）可阻止兔细胞中依赖于静息的火花频率降低。这些结果表明，SR钙含量的升高可增加钙火花频率。与兔细胞不同，尽管SR钙含量恒定且完全阻止了钙内流，但20秒的静息期使大鼠细胞中的火花频率逐渐增加。这表明在静息期存在与时间相关的火花概率增加，且与[Ca2+]i或SR钙无关。当通过阻断钠/钙交换防止SR钙耗竭时，这种效应在兔细胞中也很明显。通过无钙灌流刺激大鼠钠/钙交换介导的钙外流（这会缓慢耗尽SR钙含量）可使正常的依赖于静息的火花频率增加转变为降低。单个钙火花的幅度随SR钙含量的增加而增大。在钙超载状态下，随着火花频率增加，观察到火花融合或[Ca2+]i的持久局部升高。我们得出结论，钙火花的静息频率可独立地受到SR钙含量、[Ca2+]i或静息期变化的影响。后者可能反映了SR钙释放通道从失活或适应状态的恢复。
