Loss of Potassium from Stimulated Frog Muscle

Abstract

We have reported previously 1 that on stimulation rat muscles lose potassium in exchange for sodium, but that similar experiments with frog muscles showed no appreciable loss of potassium when the muscle was stimulated through its nerve. Other investigators 2 , 3 , 4 have had similar difficulty in demonstrating a loss of potassium with indirect stimulation of frog muscle. It now appears that a loss of potassium can readily be demonstrated in frog muscle if the nerve is stimulated with single shocks delivered at such a frequency that good contractions can be maintained for a period of 1.5 hours or perhaps less. If the muscle is continuously tetanized, the contractions fall off rapidly, not because of fatigue of the contractile mechanism but because of inhibition at; the myoneural junction. Thus the potassium content, which seems to be related to the contractile mechanism rather than to the excitatory mechanism, is not affected.

The frogs (Rana pipiens) were usually anesthetized with 1 cc. of 20% urethane per 100 gm. body weight (otherwise etherized or de-cerebrated). The animal was fastened to a frog board, one Achilles tendon being cut and attached to an isotonic recording lever and the corresponding sciatic nerve being in contact with stimulating electrodes. After 1.5 hours of stimulation, both legs were clamped off, the gastrocnemius (and sometimes also tibialis plus peroneus) muscles removed, squeezed gently and blotted on filter paper to remove blood, and put into weighing bottles. Wet and dry weights (110°C. to constant weight) were obtained and the residue was transferred to platinum crucibles, ashed at 500° C. overnight, and analyzed for potassium. I am indebted to my assistant, Miss Doris M. Cobb, for the potassium analyses.