Time-course of potential spread along a skeletal muscle fiber under voltage clamp.

Abstract

The equations describing the time-course of potential spread into a terminated segment of frog muscle fiber are given for the condition that a step of voltage is applied at x = .**GRAPHIC**. Measurements of .**GRAPHIC**. were made at 16.7-19.5.degree. C, using a 3-microelectrode voltage clamp, to compare with the theory. Best least squares fits of calculated curves to data obtained in Ringer''s solution (5 mM K) gave Gl (the radial conductance of the lumen of the tubule-T-system) = 10 .mu.mho/cm and Cm'' (surface capacitance/unit fiber length) = 1.6 .mu.F cm2. Similar measurements in 100 mM K solution, with the inward rectifier shut off by a positive prepulse, gave GL = 20 .mu.mho/cm and Cm'' = 2.0 .mu.F/cm2. The time-course of .**GRAPHIC**. measured when the inward rectifiier was fully activated by a negative prepulse, was in good agreement with the curve calculated, assuming no change in GL and Cm'' and that the only effect of the negative prepulse was to increase the conductance of surface and tubular membranes.