Peroxynitrite formation mediates LPC-induced augmentation of cardiac late sodium currents

Lysophosphatidylcholine (LPC) accumulates in the ischaemic myocardium and is arrhythmogenic. We have examined the mechanisms underlying the effects of LPC on the late cardiac Na+ current (ILNa). Na+ currents were recorded in HEK293 cells expressing NaV1.5 and isolated rat ventricular myocytes. LPC enhanced recombinant ILNa, while it reduced peak Na+ current. Computer modeling of human ventricular myocyte action potentials predicted a marked duration prolonging effect and arrhythmogenic potential due to these effects of LPC on peak and late currents. Enhancement of recombinant ILNa was suppressed by the antioxidant ascorbic acid and by the NADPH oxidase inhibitor DPI. Inhibitors of the mitochondrial electron transport chain (rotenone, TTFA and myxothiazol) were without effect on LPC responses. The superoxide donor pyrogallol was without effect on ILNa. Enhancement of ILNa was abrogated by the NOS inhibitors l-NAME and 7-nitroindazole, while LPC induced an l-NAME-sensitive production of NO, measured as enhanced DAF-FM fluorescence, in both HEK293 cells and ventricular myocytes. Despite this, the NO donors SNAP and SNP caused no change in ILNa. However, SNAP enhanced TTX-sensitive recombinant and native ILNa in the presence of pyrogallol, suggesting peroxynitrite formation as a mediator of the response to LPC. In support of this, the peroxynitrite scavenger FeTPPS prevented the response of ILNa to LPC. Peroxynitrite formation provides a novel mechanism by which LPC regulates the late cardiac Na+ current.