OBSERVATIONS ON THE ACTION POTENTIALS INDUCED BY INDIRECT STIMULATION OF SKELETAL MUSCLE IN DESOXYCORTICOSTERONE ACETATE-TREATED RATS ON A LOW POTASSIUM DIET

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Abstract
Male rats weighing 100-150 g. were fed a low K diet and injected intramusc. with 2 mg. of desoxycorticosterone acetate (DCA) daily for 3-20 days. Records of the action potentials were made with a condenser-coupled amplifier and cathode ray oscillograph. The rested gastrocnemius muscle of these animals showed repetitive action potentials for initial responses to single shocks. Repetitiveness disappeared when single shocks were repeated at the rate of 1 every 2 secs. The repetitive discharges did not arise at the point of stimulation of the nerve. The repetition was abolished by partial curarization during indirect stimulation. However, the mechanical responses induced by direct shocks in completely curarized muscle indicate that repetition occurs in DCA-treated muscle. Intraperit. injn. of KC1 in the DCA-treated animals first increased the amt. of repetition, and then abolished it. The repetition in veratrinized muscle which is not abolished by curare is more similar to the repetition in DCA-treated muscle than is the repetition in eserinized muscle. The evidence indicates that the responsiveness of the muscle fiber is modified by DCA treatment. Some similarities of the effects obtained by DCA treatment and of conditions existing in myotonia are noted.