Prolonged sarcotubular regenerative response in frog sartorius muscle

The sarcotubular system of frog sartorius muscle fibers is found to generate a prolonged depolarizing regenerative response under appropriate experimental conditions. It is shown from a point-voltage clamp analysis that the inward current component responsible for the response lasts on depolarization for hundreds of milliseconds, and reverses its sign when an equilibrium potential is exceeded. The sarcotubular response occurs in F-Ringer solution and is enhanced with EDTA. It also occurs in normal or propionate-Ringer solution containing EDTA without great change in the equilibrium potential. The response is inhibited reversibly with picrotoxin. Partial replacement of Na by K in the propionate-Ringer solution reduces the inward current component which suggests that Na may be the responsible ions.