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 Ca2+, and replacement of Ca2+ with Mn2+ 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.