Resting and action potentials in red and white muscles of the rat.

Abstract

The resting and acting potentials of the extensor digitorum longus (EDL) and soleus (SOL) muscle fibers were measured with a glass-capillary microelectrode, EDL muscle fibers show, on the average, a greater resting potential magnitude and a larger action potential amplitude than those in SOL muscle fibers. The max. rates of rise and of fall is greater in the former than in the latter. The differences in the electrical properties between the EDL and SOL were found to be correlated with a greater [K] i and a smaller [Na] i in the former than in the latter.Electrical parameters in individual muscle fibers showed an overlap between the EDL and SOL, suggesting that no clear demarcation can be made between the red and white muscle fibers. It is concluded that the red and white muscles are not essentially different from each other and that the difference is only quantitative.