THE EFFECTS OF SUCCINYLCHOLINE, DECAMETHONIUM, HEXACARBACHOLINE, GALLAMINE AND DIMETHYL TUBOCURARINE ON THE TWITCH AND TONIC NEUROMUSCULAR SYSTEMS OF THE CAT

¹ Departments of Anesthexiology and Ophthalmology, Columbia Univereity, College of Physicians and Surgeons and the Anesthesiology Department of the Presbyterian Hospital, New York, New York

The effects of neuromuscular blocking agents on the oculomotor-superior rectus and sciatic-tibialis nervemuscle preparations were determined in pentobarbital-anesthetized cats. Intravenous injections of dimethyl tubocurarine and gallamine depressed the twitch responses of the superior rectus and tibialis muscles. Although there was some variation in magnitude and duration of effect, the sensitivity of the two muscles to these agents was generally similar and the commonly stated marked sensitivity of extraocular muscle to neuromuscular blocking agents was not observed. These agents did not increase the superior rectus muscle tension. Intravenous injections of succinylcholine, decamethonium and hexacarbacholine increased superior rectus muscle tension and decreased the twitch responses of the superior rectus and tibialis muscles. Small doses of these drugs increased superior rectus muscle tension without depressing the twitch response of either muscle. Larger doses produced a greater and more prolonged increase in superior rectus muscle tension and a decrease in tibialis twitch response and superior rectus twitch response. The depression of the tibialis and superior rectus twitch responses were attributed to the effect of the depolarizing and nondepolarizing agents on the twitch system (characterized by large diameter nerve fibers, en plaque nerve endings and Fibrillenstruktur muscle fibers). The increase in superior rectus muscle tension was attributed to the effect of the depolarizing agents on the tonic system (characterized by small diameter nerve fibers, en grappe nerve endings and Felderstruktur muscle fibers).