Separation of insulin effects on K content and O2 consumption of frog muscle with cardiac glycosides.

Digoxin, deslanoside, or ouabain, in concentrations ranging from 10–9 to 10–4 m, caused a net loss of potassium from isolated intact frog skeletal muscle in the presence of lactate as substrate. The glycosides in concentrations of 10–7 to 10–4 m had little or no effect on oxygen consumption, and the stimulation of oxygen consumption by insulin was not affected by the addition of 1 µm of any of the glycosides. However, the insulin stimulation of potassium uptake by the muscle was completely blocked by digoxin and almost completely blocked by deslanoside. Insulin and ouabain together caused a greater net loss of potassium than did ouabain alone. Although the mechanisms of these effects on muscle potassium by insulin-glycoside combinations are not fully understood, a possible interpretation is that insulin acts on at least two separate sites in skeletal muscle, the potassium transfer system, and the lactate oxidation mechanism, only the first of which is influenced by cardiac glycosides.