Excitation-contraction uncoupling of striated muscle fibres by formamide treatment: evidence of detubulation.

A reportedly new technique of excitation-contraction uncoupling of frog skeletal muscle fibres was evaluated by low-frequency linear cable analysis and electron microscopy. Results indicate a similarity between the electrophysiological and ultrastructural effects of the formamide procedure and those obtained with conventional glycerol shock. Fibres in isolated frog sartorius muscles immersed in a frog Ringer's-formamide solution showed a rapid decline in twitch tension and a decrease in specific membrane capacitance, and disruption of the morphology of the transverse tubule system. These results are consistent with physical and electrical isolation of the transverse tubular network from the surface membrane of the muscle fibre ("detubulation"). However, reduction of twitch tension is marked in the formamide solution. Complete paralysis is only achieved following the return to normal Ringer's. Probably due to the greater membrane permeability of formamide, the technique requires less time and may be more reliable than the standard glycerol shock procedure.