Functional and binding evidence of taurine inhibition of alpha-adrenoceptor effects on guinea-pig ventricle.

The effect of taurine on alpha- and beta-mediated positive inotropic effects was investigated in guinea-pig ventricular strips. Loading with taurine dose-dependently antagonized the phenylephrine-induced positive inotropic effect while it was ineffective on beta-mediated positive inotropic effect. The superfusion with a taurine-free medium determined a loss of intracellular taurine, while the loading with 20 mM taurine prevented this depletion. Preincubation of cardiac membranes with different concentrations of taurine (1 to 20 mM) decreased 3H-prazosin binding, and the saturation curve obtained after preincubation of cardiac membranes with 20 mM taurine showed that taurine had a more marked effect on the number of binding sites. In both experimental models, beta-alanine did not mimic any taurine effects, suggesting that taurine actions might be specific.