Effects of ouabain on sodium uptake by frog heart and skeletal muscle.

Effects of ouabain (10(-3)-10(-12) M) on frog heart and skeletal muscle net uptake of Na from a K-free Conway-Ringer solution at 0-2 degrees C were investigated. Under these circumstances Na pumps are inactive and fibers are gaining Na even without ouabain. Changes in K, H2O, and solids were also measured. Na gains and K losses were increased by ouabain at greater than 10(-6) and greater than 10(-7) M, respectively, and decreased in heart muscle at less than or equal to 10(-8) M. It is suggested that these effects are due to actions on membrane permeability. Implications for mechanisms of positive inotropic effect of glycosides and for treatment are discussed.