Single-channel currents activated by curare in cultured embryonic rat muscle.

Single cholinergic receptor channel currents activated by curare were recorded in tissue-cultured embryonic rat muscle, directly confirming curare's action as a weak cholinergic agonist. In embryonic muscle, curare, in addition to its classical action as a competitive cholinergic antagonist, produces small sustained depolarizations which can be blocked by alpha-bungarotoxin. The single-channel events are of short duration but otherwise exhibit the major features observed with other cholinergic agonists. The single-channel events are blocked by alpha-bungarotoxin. Two values of unit conductance, 30.4 +/- 3.5 pS and 47 +/- 6 pS, were measured in cells from different cultures. Histograms of open-state duration are well fit by a distribution which is a sum of two exponentials, with time constants of 0.33 +/- 0.08 msec for the fast component and 1.84 +/- 0.43 msec for the slow component.