Stimulation of protein kinase C inhibits bursting in disease-linked mutant human cardiac sodium channels

Abstract

Background - Mutations in SCN5A, the gene coding for the human cardiac Na+ channel α-subunit, are associated with variant 3 of the long-QT syndrome (LQT-3). Several LQT-3 mutations promote a mode of Na+ channel gating in which a fraction of channels fail to inactivate, contributing sustained Na+ channel current (Isus), which can delay repolarization and prolong the QT interval. Here, we investigate the possibility that stimulation of protein kinase C (PKC) may modulate Isus, which is prominent in disease-related Na+ channel mutations. Methods and Results - We measured the effects of PKC stimulation on Na+ currents in human embryonic kidney (HEK 293) cells expressing 3 previously reported disease-associated Na+ channel mutations (Y1795C, Y1795H, and AKPQ). We find that the PKC activator 1-oleoyl-2-acetyl-sn-glycerol (OAG) significantly reduced Isus in the mutant but not wild-type channels. The effect of OAG on Isus was reduced by the PKC inhibitor staurosporine (2.5 μmol/L), ablated by the mutation S1503A, and mimicked by the mutation S1503D. Isus recorded in myocytes isolated from mice expressing ΔKPQ channels was similarly inhibited by OAG exposure or stimulation of α1-adrenergic receptors by phenylephrine. The actions of phenylephrine on Isus were blocked by the PKC inhibitor chelerythrine. Conclusions - We conclude that stimulation of PKC inhibits channel bursting in disease-linked mutations via phosphorylation-induced alteration of the charge at residue 1503 of the Na+ channel α-subunit. Sympathetic nerve activity may contribute directly to suppression of mutant channel bursting via α-adrenergic receptor-mediated stimulation of PKC.