Purification and characterization of endogenous digitalis-like substance (DLS) from pig heart

This study was undertaken to further purify and characterize a crude DLS-containing fraction isolated from left ventricular tissue of pig heart. The crude fraction, on purification, separated into three fractions designated as C1, C2 and C3. Only fraction C1 produced positive inotropic response on isolated perfused guinea pig heart. Fraction C1 specifically inhibited rat heart Na+, K(+)-ATPase, whereas fractions C2 and C3 were found to be non-specific inhibitors. Studies with cardiac Na+, K(+)-ATPase, its interaction in the presence of increasing concentration of [K+] and competitive displacement of [3H]-ouabain binding, demonstrated fraction C1 to have ouabain-like properties. C1 also inhibited dog kidney Na+, K(+)-ATPase activity in a dose-dependent manner and was found to be devoid of catecholamines, peptides and lipids. Fraction C1 was found to be heat sensitive and its inotropic activity was destroyed on ashing at 500 degrees C. These studies provide further evidence for the presence of an endogenous DLS in mammalian heart.