Inhibition of endogenous late Na+ current with TTX or ranolazine shortened MAPD90, decreased repolarization dispersion, and abolished torsade de pointes in hearts with reduced repolarization reserve.
Does inhibition of late Na+ current with TTX or ranolazine prevent arrhythmogenesis in isolated rabbit hearts with reduced repolarization reserve?
Inhibition of endogenous late Na+ current with ranolazine or TTX reverses action potential prolongation and abolishes torsade de pointes in rabbit hearts with reduced repolarization reserve.
p-value: p=<0.01
Reduction of repolarization reserve increases the risk of arrhythmia. We hypothesized that inhibition of K(+) current (I(K)) to decrease repolarization reserve would unmask the proarrhythmic role of endogenous, physiological late Na(+) current (late I(Na)). Monophasic action potentials (MAP) and 12-lead electrocardiogram were recorded from female rabbit isolated hearts. To block I(K) and reduce repolarization reserve, E-4031, 4-aminopyridine, and BaCl(2) were used; to block endogenous late I(Na), tetrodotoxin (TTX) and ranolazine were used. E-4031 (1-60 nM) concentration-dependently prolonged MAP duration (MAPD(90)) and increased duration of the T wave from T(peak) to T(end) (T(peak)-T(end)), transmural dispersion of repolarization (TDR), and beat-to-beat variability (BVR) of MAPD(90). E-4031 caused spontaneous and pause-triggered polymorphic ventricular tachycardia torsade de pointes (TdP). In the presence of 60 nM E-4031, TTX (0.6-3 muM) and ranolazine (5-10 muM) shortened MAPD(90), decreased TDR, BVR, and T(peak)-T(end) (n = 9-20, P < 0.01), and abolished episodes of TdP. In hearts treated with BaCl(2) or 4-aminopyridine plus E-4031, TTX (0.6-3 muM) shortened MAPD(90) and decreased T(peak)-T(end). Ranolazine could not reverse the effect of E-4031 to inhibit human ether-a-go-go-related gene (HERG) K(+) current; thus, the reversal by ranolazine of effects of E-4031 was likely due to inhibition of late I(Na) and not to antagonism of the HERG-blocking action of E-4031. We conclude that endogenous, physiological late I(Na) contributes to arrhythmogenesis in hearts with reduced repolarization reserve. Inhibition of this current partially reverses MAPD prolongation and abolishes arrhythmic activity caused by I(K) inhibitors.
Wu et al. (Sat,) conducted a other in Arrhythmia. Tetrodotoxin (TTX) and ranolazine vs. E-4031 alone was evaluated on MAPD90, TDR, BVR, and Tpeak-Tend (p=<0.01). Inhibition of endogenous late Na+ current with TTX or ranolazine shortened MAPD90, decreased repolarization dispersion, and abolished torsade de pointes in hearts with reduced repolarization reserve.