Immunocytochemical localization of alpha-actinin in frog muscle treated with the ionophore A23187.

Incubation of frog skeletal muscle with the ionophore A23187 induces severe damage in the muscle. At the level of the Z line, the ionophore induces redistribution and release of the protein alpha-actinin, as shown by immunocytochemical techniques. The ionophore does not induce damage in denervated preparations or in preparations pretreated with d-tubocurarine, which indicates that the effect is indirect and neurally mediated. It is concluded that the increase in spontaneous transmitter release produced by the ionophore induces Ca2+ influx through the acetylcholine receptor. Calcium ions activate neutral proteases which release alpha-actinin from the Z line.