Changes in membrane potentials, K content, and fiber structure in irradiated frog sartorius muscle

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Abstract
Changes in membrane potential, K content, and fiber structure were studied in excised frog sartorius muscles that had received massive single doses (50–200 kr) of ionizing radiation. With muscle in normal Ringer's solution at 25°C, the median membrane potential declined and K leakage increased progressively, as measured at intervals, after exposure doses above ∼100 kr; in K-rich Ringer's solution, decline was appreciably slower. In individual irradiated fibers, membrane potentials recorded at different points along a fiber tended to be nonuniform. When subsequent histologic alteration occurred, it often originated as a focal disorganization of structure in a region of minimum membrane potential. Visible pathologic changes resembled in part Zenker degeneration in intact muscle. It is suggested that decline in membrane potential, histologic changes, and increased K leakage are different expressions of the same basic radiation lesion. Radiation-induced changes were markedly retarded by posttreatment storage at 3°C.