Contractile and chemosensitive properties of muscle treated with calcium ionophore A23187. Comparison with dystrophic muscle.

Rat diaphragms were treated with calcium ionophore, A23187, for 60 min at 37 degrees C, and twitch, tetanus and their derivatives were studied on the basis of the active state concept. Results were than compared with those of human dystrophic muscle. Like dystrophic muscle, maximum tetanic force and maximum velocity of tetanus development were markedly reduced. Changes in twitch parameters, which tend to appear in an early stage of muscular dystrophy, were not noted after the treatment with this ionophore, except alterations relating to prolongation of the active state. Twitch/tetanus ratio was thus increased, while it was decreased in dystrophic muscle. Isoproterenol-induced change of twitch was normally seen in the A23187-treated muscle, while dystrophic muscle responded to catecholamine in a manner different from control. Therefore, the muscle treated with calcium ionophore is not wholly similar to dystrophic muscle.