ACTION OF PROCAINE ON FROG SKELETAL MUSCLE

¹ Department of Pharmacology and Therapeutics, University of Manitoba Faculty of Medicine, Winnipeg, Canada

The mechanism of the blocking action of procaine on the electrical activity of frog skeletal muscle was investigated using intracellular microelectrode techniques. Studies of the current-voltage relations of the fibers demonstrated that procaine suppressed the specific increase in sodium conductance ("local response") which normally follows an adequate stimulus. This was the only observed change produced by procaine in either the passive or active electric properties of the fiber membranes which could account for the well-known increase in the threshold for electrical stimulation caused by this drug. In accord with this suggested mechanism of action, procaine decreased the rate of rise and the amplitude of the action potential. Both these effects could be antagonized by the addition of excess sodiumn chloride to the procaine-Ringer's solution bathing the muscle. The results suggested a competition between procaine and extracellular sodium ions with 0.5 x 10^-4 g/ml of procaine being approximately equivalent to a 50% reduction in the external sodium concentration.