Actions of G-strophanthin, adrenaline and acetylcholine on bullfrog ventricular muscle in the sodium-free lithium solution.

The actions of g-strophanthin, adrenaline and acetylcholine on the action potential of bullfrog ventricular muscle were studied in the Na+ -free Li+ solution, in order to examine if these actions are associated with the change of active Na+ transport. The action of g-strophanthin on the action potential, being observed in the Ringer solution, completely disappeared in the Na+-free Li+ solution. On the other hand, the actions of adrenaline and acetylcholine remained unchanged in the Na+ -free Li+ solution, except the hyperpolarizing action of adrenaline on the resting membrane. These results suggest that changes of the action potential by g-strophanthin are secondary events caused by the change of active Na+ transport, whereas those by adrenaline and acetylcholine are primary events due to the change of membrane permeability.