Pharmacophysiological study on muscle treated with calcium ionophore A23187

Muscle treated with A23187, which raises intracellular free Ca2+ concentration, was studied to elucidate effects on membrane properties. The mean resting membrane potential was reduced; it was normally depolarized by ouabain but not significantly hyperpolarized by epinephrine and insulin. In the presence of ouabain, membrane depolarization was not provoked by insulin. The results imply a defect of active Na+-transport of the membrane after exposure to a calcium ionophore.