Excitation-contraction coupling in Na+-Ca2+ exchanger knockout mice -: Reduced transsarcolemmal Ca2+ flux
Excitation-contraction coupling in Na+-Ca2+ exchanger knockout mice -: Reduced transsarcolemmal Ca2+ flux
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DOI：
10.1161/01.res.0000196563.84231.21
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发表时间：
2005-12-09
影响因子：
20.1
通讯作者：
Goldhaber, JI
中科院分区：
文献类型：
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作者：
Pott, C;Philipson, KD;Goldhaber, JI
心脏特异的钠-钙交换(NCX)基因敲除(KO)小鼠令人惊讶地存活到成年，而蛋白质表达水平没有代偿性变化。为了确定在没有NCX的情况下心脏功能是如何维持的，我们研究了野生型(WT)和NCX基因敲除小鼠全细胞膜片钳心肌细胞的膜电流、细胞内钙离子和动作电位(APs)。KO组和WT组的静息钙和肌浆网钙负荷无明显差异。在长时间的咖啡因暴露中，KO和WT心肌细胞钙瞬变的下降速度显著减慢，这表明没有替代的钙排出机制来补偿NCX的缺乏。KO细胞的L型钙电流(I-Ca)峰值较WT细胞降低62%。然而，相应的钙瞬变是相似的，这意味着KO细胞兴奋-收缩偶联的增益增加。KO细胞记录的AP复极速度比WT细胞快。在WT细胞中，施加KO AP波型电压钳可使通过I-Ca的钙内流减少59%。同样，相应的钙瞬变也是相似的。我们的发现表明，NCX KO细胞通过减少ICA和缩短AP，将钙内流限制在WT的20%左右。由于AP更快的复极化和一种未知的AP非依赖性机制，兴奋收缩耦合的增益增加，从而维持了收缩能力。
Cardiac-specific Na+-Ca2+ exchanger (NCX) knockout ( KO) mice surprisingly survive into adulthood without compensatory changes in protein expression levels. To determine how cardiac function is maintained in the absence of NCX, we investigated membrane currents, intracellular Ca2+, and action potentials (APs) in whole cell patch-clamped myocytes from wild-type (WT) and NCX knockout mice. There was no difference in resting Ca2+ or sarcoplasmic reticular Ca2+ load between KO and WT. During prolonged caffeine exposure, the decrease of the Ca2+ transient was drastically slowed in KO versus WT myocytes, indicating that no alternative Ca2+-extrusion mechanism is upregulated to compensate for the absence of NCX. Peak L-type Ca2+ current (I-Ca) was reduced by 62% in KO myocytes compared with WT. Nevertheless, the corresponding Ca2+ transients were similar, implying an increase in the gain of excitation-contraction coupling in KO cells. APs recorded from KO cells repolarized more rapidly than in WT. In WT myocytes, applying a KO AP waveform voltage clamp reduced Ca2+ influx via I-Ca by 59% compared with WT AP waveform clamps. Again, the corresponding Ca2+ transients remained similar. Our findings indicate that NCX KO myocytes limit Ca2+ influx to approximate to 20% of that in WT by reducing ICa and by abbreviating the AP. Contractility is maintained by an increase in the gain of excitation contraction coupling resulting from both a more rapid repolarization of the AP and an as yet unidentified AP-independent mechanism.