Nav1.5-dependent persistent Na+ influx activates CaMKII in rat ventricular myocytes and N1325S mice

Yao L, Fan P, Jiang Z, Viatchenko-Karpinski S, Wu Y, Kornyeyev D, Hirakawa R, Budas GR, Rajamani S, Shryock JC, Belardinelli L. Na(v)1.5-dependent persistent Na+ influx activates CaMKII in rat ventricular myocytes and N1325S mice. Am J Physiol Cell Physiol 301: C577-C586, 2011. First published June 15, 2011; doi: 10.1152/ajpcell.00125.2011.-Late Na+ current (I-NaL) and Ca2+/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 Ca2+ 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 (N1325S). The effects of both ATX-II and the N1325S 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 N1325S 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 per-fused 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.