Department of Biology, Gilead Sciences, Palo Alto, California 94304, USA.
Am J Physiol Cell Physiol. 2011 Sep;301(3):C577-86. doi: 10.1152/ajpcell.00125.2011. Epub 2011 Jun 15.
Late Na(+) current (I(NaL)) and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) are both increased in the diseased heart. Recently, CaMKII was found to phosphorylate the Na(+) channel 1.5 (Na(v)1.5), resulting in enhanced I(NaL). Conversely, an increase of I(NaL) would be expected to cause elevation of intracellular Ca(2+) and activation of CaMKII. However, a relationship between enhancement of I(NaL) and activation of CaMKII has yet to be demonstrated. We investigated whether Na(+) influx via Na(v)1.5 leads to CaMKII activation and explored the functional significance of this pathway. In neonatal rat ventricular myocytes (NRVM), treatment with the I(NaL) activators anemone toxin II (ATX-II) or veratridine increased CaMKII autophosphorylation and increased phosphorylation of CaMKII substrates phospholamban and ryanodine receptor 2. Knockdown of Na(v)1.5 (but not Na(v)1.1 or Na(v)1.2) prevented ATX-II-induced CaMKII phosphorylation, providing evidence for a specific role of Na(v)1.5 in CaMKII activation. In support of this view, CaMKII activity was also increased in hearts of transgenic mice overexpressing a gain-of-function Na(v)1.5 mutant (N(1325)S). The effects of both ATX-II and the N(1325)S mutation were reversed by either I(NaL) inhibition (with ranolazine or tetrodotoxin) or CaMKII inhibition (with KN93 or autocamtide 2-related inhibitory peptide). Furthermore, ATX-II treatment also induced CaMKII-Na(v)1.5 coimmunoprecipitation. The same association between CaMKII and Na(v)1.5 was also found in N(1325)S mice, suggesting a direct protein-protein interaction. Pharmacological inhibitions of either CaMKII or I(NaL) also prevented ATX-II-induced cell death in NRVM and reduced the incidence of polymorphic ventricular tachycardia induced by ATX-II in rat perfused hearts. Taken together, these results suggest that a Na(v)1.5-dependent increase in Na(+) influx leads to activation of CaMKII, which in turn phosphorylates Na(v)1.5, further promoting Na(+) influx. Pharmacological inhibition of either CaMKII or Na(v)1.5 can ameliorate cardiac dysfunction caused by excessive Na(+) influx.
钠电流（I(NaL)）和钙/钙调蛋白依赖性蛋白激酶 II（CaMKII）在病变心脏中均增加。最近，发现 CaMKII 可磷酸化钠通道 1.5（Na(v)1.5），导致 I(NaL)增强。相反，I(NaL)的增加预计会导致细胞内 Ca(2+)升高和 CaMKII 激活。然而，增强的 I(NaL)与 CaMKII 激活之间的关系尚未得到证明。我们研究了通过 Na(v)1.5 的钠内流是否会导致 CaMKII 激活，并探讨了该途径的功能意义。在新生大鼠心室肌细胞（NRVM）中，用 I(NaL)激动剂海葵毒素 II（ATX-II）或维拉帕米处理会增加 CaMKII 自身磷酸化，并增加 CaMKII 底物肌浆网磷蛋白和兰尼碱受体 2 的磷酸化。Na(v)1.5 的敲低（但不是 Na(v)1.1 或 Na(v)1.2）可防止 ATX-II 诱导的 CaMKII 磷酸化，这为 Na(v)1.5 在 CaMKII 激活中的特定作用提供了证据。支持这一观点，过表达具有功能获得性 Na(v)1.5 突变（N(1325)S）的转基因小鼠的心脏中 CaMKII 活性也增加。ATX-II 和 N(1325)S 突变的作用均被 I(NaL)抑制（用雷诺嗪或河豚毒素）或 CaMKII 抑制（用 KN93 或自噬相关抑制肽）逆转。此外，ATX-II 处理还诱导 CaMKII-Na(v)1.5 共免疫沉淀。在 N(1325)S 小鼠中也发现了 CaMKII 和 Na(v)1.5 之间的相同关联，提示存在直接的蛋白质-蛋白质相互作用。CaMKII 或 I(NaL)的药理学抑制也可防止 ATX-II 诱导的 NRVM 细胞死亡，并降低 ATX-II 在大鼠灌流心脏中诱导的多形性室性心动过速的发生率。总之，这些结果表明，Na(v)1.5 依赖性钠内流增加导致 CaMKII 激活，进而使 Na(v)1.5 磷酸化，进一步促进钠内流。CaMKII 或 Na(v)1.5 的药理学抑制可改善由过度钠内流引起的心脏功能障碍。
