Intracellular [Na+] modulates synergy between Na+/Ca2+ exchanger and L-type Ca2+ current in cardiac excitation-contraction coupling during action potentials
Intracellular [Na+] modulates synergy between Na+/Ca2+ exchanger and L-type Ca2+ current in cardiac excitation-contraction coupling during action potentials
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DOI：
10.1007/s00395-011-0202-z
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发表时间：
2011-11-01
影响因子：
9.5
通讯作者：
Backx, Peter H.
中科院分区：
文献类型：
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作者：
Ramirez, Rafael J.;Sah, Rajan;Backx, Peter H.
心肌细胞的兴奋收缩偶联涉及L型钙通道触发肌浆网钙离子释放，其活性受动作电位(AP)谱的强烈影响。钙离子通过Na~+/Ca~(2+)交换器(NCX)内流在ECC反应AP时触发SR钙释放的作用尚不清楚。为了分离NCX对肌浆网钙释放的影响，用共聚焦显微镜记录膜片钳大鼠心室肌细胞[Ca~(2+)](I)固定在150nmol/L时的Ca~(2+)峰释放，结果表明，当[Na~+](I)从0增加到20 mm ol/L时，[Na+](I)呈乙状结状增加，并随着[Na~+](I)升高而倍增，这种[Na+](I)依赖不依赖于i(Na)和SR Ca~(2+)负荷，在我们的实验条件下，这种[Na~+](I)依赖性与肌浆Ca~(2+)负荷无关。然而，用KB-R7943或XIP抑制NCX使20 mmoL/L[Na+](I)组的Delta F/F(0)波幅降低，而5 mmoL/L[Na+](I)组[Na+](I)不降低。在膜复极化至-15 mV之前，肌浆网钙离子完全释放，表明钙离子进入二分体(不是减少挤出)是[Na+](I)依赖的ECC增强的基础。由于50 mm o l/L Cd~(2+)抑制心肌细胞[Ca~(2+)]i可抑制心肌细胞内钙尖峰活动，因此我们的实验结果表明，在心动过速时，NCX通过协同提高I(Ca，L)介导的细胞外钙通道的效率而促进肌浆网钙离子释放。
Excitation-contraction coupling (ECC) in cardiac myocytes involves triggering of Ca2+ release from the sarcoplasmic reticulum (SR) by L-type Ca channels, whose activity is strongly influenced by action potential (AP) profile. The contribution of Ca2+ entry via the Na+/Ca2+ exchanger (NCX) to trigger SR Ca2+ release during ECC in response to an AP remains uncertain. To isolate the contribution of NCX to SR Ca2+ release, independent of effects on SR Ca2+ load, Ca2+ release was determined by recording Ca2+ spikes using confocal microscopy on patch-clamped rat ventricular myocytes with [Ca2+](i) fixed at 150 nmol/L. In response to AP clamps, normalized Ca2+ spike amplitudes (Delta F/F (0)) increased sigmoidally and doubled as [Na+](i) was elevated from 0 to 20 mmol/L with an EC50 of similar to 10 mmol/L. This [Na+](i)-dependence was independent of I (Na) as well as SR Ca2+ load, which was unchanged under our experimental conditions. However, NCX inhibition using either KB-R7943 or XIP reduced Delta F/F (0) amplitude in myocytes with 20 mmol/L [Na+](i), but not with 5 mmol/L [Na+](i). SR Ca2+ release was complete before the membrane repolarized to -15 mV, indicating Ca2+ entry into the dyad (not reduced extrusion) underlies [Na+](i)-dependent enhancement of ECC. Because I (Ca,L) inhibition with 50 mmol/L Cd2+ abolished Ca2+ spikes, our results demonstrate that during cardiac APs, NCX enhances SR Ca2+ release by synergistically increasing the efficiency of I (Ca,L)-mediated ECC.