Neurotransmitter action on the membrane of Mytilus smooth muscle—I. Acetylcholine

1. 1. Iontophoretic application of acetylcholine (ACh) on smooth muscle fibers of the anterior byssus retractor muscle of Mytilus edulis L. evoked a depolarizing potential with a half-decay time of 10 sec. 2. 2. The ACh potential varied with the external concentrations of Na + and K +, but not Cl −, suggesting that it was generated by increased conductance to Na + and K +. 3. 3. The reversal potential for the ACh potential, estimated by extrapolation, was −13 ± 5 mV, similar to that estimated for the excitatory junction potential (−12 ± 5 mV), suggesting that both may be generated by the same change in conductance and supporting the hypothesis that the excitatory neurotransmitter is ACh.