Background: Women have longer QTc intervals than men and are at greater risk for arrhythmias associated with long QTc intervals, such as drug-induced torsade de pointes. Recent clinical and experimental data suggest an important role of testosterone in sex-related differences in ventricular repolarization. However, studies on effects of testosterone on ionic currents in cardiac myocytes are limited.
Methods and results: We examined effects of testosterone on action potential duration (APD) and membrane currents in isolated guinea pig ventricular myocytes using patch-clamp techniques. Testosterone rapidly shortened APD, with an EC50 of 2.1 to 8.7 nmol/L, which is within the limits of physiological testosterone levels in men. APD shortening by testosterone was mainly due to enhancement of slowly activating delayed rectifier K+ currents (IKs) and suppression of L-type Ca2+ currents (I(Ca,L)), because testosterone failed to shorten APD in the presence of an IKs inhibitor, chromanol 293B, and an I(Ca,L) inhibitor, nisoldipine. A nitric oxide (NO) scavenger and an inhibitor of NO synthase 3 (NOS3) reversed the effects of testosterone on APD, which suggests that NO released from NOS3 is responsible for the electrophysiological effects of testosterone. Electrophysiological effects of testosterone were reversed by a blocker of testosterone receptors, a c-Src inhibitor, a phosphatidylinositol 3-kinase inhibitor, and an Akt inhibitor. Immunoblot analysis revealed that testosterone induced phosphorylation of Akt and NOS3.
Conclusions: The nontranscriptional regulation of IKs and I(Ca,L) by testosterone is a novel regulatory mechanism of cardiac repolarization that can potentially contribute to the control of QTc intervals by androgen.