Abstract
In frog sciatic nerve-iliofibularis and trigeminal nerve-masseter preparations, succinylcholine (Sch) contracture appeared to be due to a postsynaptic depolarization of neuromuscular junctions distributing multiply along the whole muscle fiber length. A presynaptic effect of Sch was noted; antidromic discharges were recorded in the ventral root. This effect appeared at a lower concentrations than those producing the contracture, while no antidromic discharges were evoked at concentrations producing the contracture. The amplitude of the miniature small nerve junc-tional potentials decreased with development of depolarization by Sch while the frequency did not change. In frog sciatic nerve-sartorius (fast muscle) preparations, Sch elicited fibrillary twitching but no contracture. The membrane depolarization of the muscle by Sch was localized at the single or double end-plate regions.