Molecular requirements for L-type Ca 2+ channel blockade by testosterone

Abstract

Despite being generally perceived as detrimental to the cardiovascular system, testosterone has marked beneficial vascular effects; most notably it acutely and directly causes vasodilatation. Indeed, men with hypotestosteronaemia can present with myocardial ischemia and angina which can be rapidly alleviated by infusion of testosterone. To date, however, in vitro studies have failed to provide a convincing mechanism to account for this clinically important effect. Here, using whole-cell patch-clamp recordings to measure current flow through recombinant human L-type Ca 2+ channel α 1C subunits (Ca v1.2), we demonstrate that testosterone inhibits such currents in a concentration-dependent manner. Importantly, this occurs over the physiological range of testosterone concentrations (IC 50 34 nM), and is not mimicked by the metabolite 5α-androstan-17β-ol-3-one (DHT), nor by progesterone or estradiol, even at high (10 μM) concentration. L-type Ca 2+ channels in the vasculature are also important clinical targets for vasodilatory dihydropyridines. A single point mutation (T1007Y) almost completely abolishes nifedipine sensitivity in our recombinant expression system. Crucially, the same mutation renders the channels insensitive to testosterone. Our data strongly suggest, for the first time, the molecular requirements for testosterone binding to L-type Ca 2+ channels, thereby supporting its beneficial role as an endogenous Ca 2+ channel antagonist in the treatment of cardiovascular disease.