The response of Ca-mediated action potentials and contractile activity in mammalian ventricular myocardium towards alkalosis.

Alkalosis (pH 7.8) produced by reduction of CO2 concentration augmented both upstroke velocity of Ca action potentials and isometric contractile force of mammalian heart muscle. If the increase of pH to 7.8 was achieved by a raise of HCO3 concentration (with simultaneous reduction of CO2 concentration), the positive inotropic response was not accompanied by an augmented Ca current. Obviously, the well-known positive inotropic effect of alkalosis does not only depend upon the enhancement of transmembrane Ca influx during excitation, but can be mediated alone by affecting intracellular Ca movements as well.