Effect of ionic medium on carbacholine-induced membrane depolarization in lumbricus terrestris somatic muscle cells

Carbacholine depolarizes Lumbricus terrestris myocyte membrane. Addition of verapamil, tetrodotoxin, removal of K(+), Cl(-), and Ca(2+), and replacement of Ca(2+)with Mn(2+)in the bathing solution did not prevent the carbacholine-induced decrease in resting potential, but in a sodium-free medium carbacholine was ineffective. It was hypothesized that depolarization of the sarcolemma resulting from activation of cholinomimetic-sensitive channel-receptor complex of the Lumbricus terrestris somatic muscle cells is primarily determined by sodium permeability of the membrane.