Sites of action of lead on spontaneous transmitter release from motor nerve terminals.

Lead ions have potent neurotoxic activities. At the neuromuscular junction, they depress the neurally evoked release, but strongly facilitate the spontaneous release of transmitter quanta from motor nerve terminals. The mechanisms underlying the latter action of lead were studied in the isolated frog neuromuscular preparation. The evidence presented in this article is consistent with the hypothesis that lead ions inhibit some membranal and intracellular calcium regulatory mechanisms, consequently producing an increase in the intraterminal concentration of ionized calcium, and hence, in spontaneous transmitter release.