Contribution of the neuronal sodium channel Nav1.8 to sodium- and calcium-dependent cellular proarrhythmia

Objective: In myocardial pathology such as heart failure a late sodium current (I-NaL) augmentation is known to be involved in conditions of arrhythmogenesis. However, the underlying mechanisms of the I-NaL generation are not entirely understood. By now evidence is growing that non-cardiac sodium channel isoforms could also be involved in the I-NaL generation. The present study investigates the contribution of the neuronal sodium channel isoform Na(v)1.8 to arrhythmogenesis in a clearly-defined setting of enhanced I-NaL by using anemone toxin II (ATX-II) in the absence of structural heart disease. Methods: Electrophysiological experiments were performed in order to measure I-NaL, action potential duration (APD), SR-Ca2+-leak and cellular proarrhythmic triggers in ATX-II exposed wild-type (WT) and SCN10A(-/-) mice cardiomyocytes. In addition, WT cardiomyocytes were stimulated with ATX-II in the presence or absence of Na(v)1.8 inhibitors. I-NCX was measured by using the whole cell patch clamp method. Results: In WT cardiomyocytes exposure to ATX-II augmented I-NaL, prolonged APD, increased SR-Ca2+-leak and induced proarrhythmic triggers such as early afterdepolarizations (EADs) and Ca2+-waves. All of them could be significantly reduced by applying Na(v)1.8 blockers PF-01247324 and A-803467. Both blockers had no relevant effects on cellular electrophysiology of SCN10A(-/-) cardiomyocytes. Moreover, in SCN10A(-/-)-cardiomyocytes, the ATX-II-dependent increase in I-NaL, SR-Ca2+-leak and APD prolongation was less than in WT and comparable to the results which were obtained with WT cardiomyocytes being exposed to ATX-II and Na(v)1.8 inhibitors in parallel. Moreover, we found a decrease in reverse mode NCX current and reduced CaMKII-dependent RyR2-phosphorylation after application of PF-01247324 as an underlying explanation for the Na+-mediated Ca2+-dependent proarrhythmic triggers. Conclusion: The current findings demonstrate that Na(v)1.8 is a significant contributor for I-NaL-induced arrhythmic triggers. Therefore, Na(v)1.8 inhibition under conditions of an enhanced I-NaL constitutes a promising antiarrhythmic strategy which merits further investigation.