Effect of glycerol treatment on the calcium current of frog skeletal muscle.

1. Current and voltage clamp experiments were carried out on frog skeletal muscle fibres. For voltage clamp, the three micro-electrode technique near the fibre end was used. 2. Calcium spikes and currents were recorded in TEA sulphate saline. The addition of 400 mM-glycerol did not appreciably modify them. 3. Muscle fibers were detubulated with the glycerol method. They showed sodium propagating action potentials, with sodium and potassium currents of expected amplitudes. 4. Calcium spikes and currents were reduced or abolished in detubulated muscle fibres. 5. An analysis of fibre capacitance showed a linear correlation between the remaining ICa and the degree of electric discontinuity between the transverse tubular system and the surface membrane. 6. These results indicate that ICa is mainly located in the transverse tubular system. This localization is compatible with some role during mechanical activation.