Activation of reverse Na+-Ca2+ exchange by the Na+ current augments the cardiac Ca2+ transient: evidence from NCX knockout mice
Activation of reverse Na+-Ca2+ exchange by the Na+ current augments the cardiac Ca2+ transient: evidence from NCX knockout mice
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DOI：
10.1113/jphysiol.2010.187708
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发表时间：
2010-09-01
影响因子：
5.5
通讯作者：
Philipson, Kenneth D.
中科院分区：
文献类型：
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作者：
Larbig, Robert;Torres, Natalia;Philipson, Kenneth D.
动作电位 (AP) 期间 Na+ 流入激活反向 Na+-Ca2+ 交换 (NCX) 以及随后触发 Ca2+ 进入的假设是有争议的。我们通过在从成年野生型 (WT) 和 NCX 敲除 (KO) 小鼠中分离的膜片钳心室肌细胞中模拟动作电位之前和之后监测 I-Na 选择性失活前后的细胞内 Ca2+ 来测试这一假设。首先，我们使用 -45 mV 的斜坡预脉冲灭活 I-Na。在 WT 细胞中，I-Na 失活使 Ca2+ 瞬态幅度降低 51.1 +/- 4.6%（P < 0.001，n = 14），并将其最大释放通量降低 53.0 +/- 4.6%（P < 0.001，n = 14）。对舒张期 Ca2+ 没有影响。与此形成鲜明对比的是，NCX KO 心肌细胞中的 Ca2+ 瞬变不受 I-Na 存在或不存在的影响 (n = 8)。当测量肌浆网耗尽的肌细胞中触发 Ca2+ 流入时，我们获得了类似的结果。在 WT 细胞中，I-Na 失活使触发 Ca2+ 内流减少了 37.8 +/- 6%，在 2.5 mm 外部 Ca2+ 下最大通量减少了 30.6 +/- 7.7%（P < 0.001 和 P < 0.05，n = 9）。 KO 细胞中同样不存在这种效应 (n = 8)。其次，暴露于10μm河豚毒素来阻断I-Na也减少了WT肌细胞中的Ca2+瞬变，但不减少NCX KO肌细胞中的Ca2+瞬变。我们得出结论，I-Na 和反向 NCX 通过增加触发兰尼碱受体的 Ca2+ 池来调节小鼠 WT 心肌细胞中 Ca2+ 的释放。这是调节小鼠心脏 Ca2+ 释放和收缩力的重要机制。
The hypothesis that Na+ influx during the action potential (AP) activates reverse Na+-Ca2+ exchange (NCX) and subsequent entry of trigger Ca2+ is controversial. We tested this hypothesis by monitoring intracellular Ca2+ before and after selective inactivation of I-Na prior to a simulated action potential in patch-clamped ventricular myocytes isolated from adult wild-type (WT) and NCX knockout (KO) mice. First, we inactivated I-Na using a ramp prepulse to -45 mV. In WT cells, inactivation of I-Na decreased the Ca2+ transient amplitude by 51.1 +/- 4.6% (P < 0.001, n = 14) and reduced its maximum release flux by 53.0 +/- 4.6% (P < 0.001, n = 14). There was no effect on diastolic Ca2+. In striking contrast, Ca2+ transients in NCX KO cardiomyocytes were unaffected by the presence or absence of I-Na (n = 8). We obtained similar results when measuring trigger Ca2+ influx in myocytes with depleted sarcoplasmic reticulum. In WT cells, inactivation of I-Na decreased trigger Ca2+ influx by 37.8 +/- 6% and maximum rate of flux by 30.6 +/- 7.7% at 2.5 mm external Ca2+ (P < 0.001 and P < 0.05, n = 9). This effect was again absent in the KO cells (n = 8). Second, exposure to 10 mu m tetrodotoxin to block I-Na also reduced the Ca2+ transients in WT myocytes but not in NCX KO myocytes. We conclude that I-Na and reverse NCX modulate Ca2+ release in murine WT cardiomyocytes by augmenting the pool of Ca2+ that triggers ryanodine receptors. This is an important mechanism for regulation of Ca2+ release and contractility in murine heart.