EFFECTS OF OUABAIN ON MONO-VALENT CATION-TRANSPORT IN MAMMALIAN TISSUE

We measured the effects of ouabain sodium-potassium ATPase (Na-K ATPase) specific activity (SA) and rubidium (Rb) transport in newborn (NB) and adult (Ad) sheep myocardium (myo), guinea pig myo and red blood cells (RBC), and human RBC. 50% Inhibition of Na-K ATPase SA and Rb transport occurred at ouabain concentrations between 10-4.8 and 10-7.6 M in different species; within a species, 50% inhibition of Rb transport occurred at lower ouabain concentrations than 50% inhibition of Na-K ATPase SA. No differences between mature and immature tissues were found. Ouabain binding stability to Na-K ATPase extracted from myo and RBC did not vary with age. Binding studies revealed a KD .times. 10-8 M of 0.87 .+-. 0.09 for NB human RBC and 0.88 .+-. 0.14 for Ad human RBC. Calculated RBC receptor density however, was higher in the Ad (1.25 .+-. 0.08 sites/.mu.m2) than in the NB (1.03 .+-. 0.04 sites/.mu.m2, p < 0.01). Binding studies in extracted myocardial specimens showed a KD .times. 10-8 M of 1.23 .+-. 0.27 for NB and 1.09 .+-. 0.46 for Ad; mM ouabain bound .times. 10-12/Na-K ATPase unit were 355 .+-. 120 (SEM) for NB and 316 .+-. 51 for Ad. These studies of cardiac glycosides reveal few age-related differences in drug binding or inhibition of monovalent cation transport.