Digitalis glycosides are major tools for the identification of the Na/K ATPase as well as the Na/K fluxes mediated by this transport system. Since its discovery 50 yr ago (Schatzmann, 1953), the inhibitory effect of these compounds on the Na/K pump has been confirmed repeatedly. There has been evidence to contrary effects, although. Thus, Hougen et al. (1981) reported a stimulatory effect of nanomolar concentrations of ouabain on 86Rb uptake in guinea pig atria. This effect could be suppressed by propranolol, or by prior depletion of endogenous pools of norepinephrine in the tissue, and it was regarded as an indirect effect elicited by norepinephrine released by an action of ouabain on nerve endings in the heart.
Several others have reported stimulating effects of low concentrations of cardiac glycosides on active Na/K transport in multicellular cardiac preparations, and also in the squid axon,...
