Kinetic properties of intramembrane charge movement under depolarized conditions in frog skeletal muscle fibers.

摘要: Intramembrane charge movement was measured on skeletal muscle fibers of the frog in a single Vaseline-gap voltage clamp. Charge movements determined both under polarized conditions (holding potential, VH = -100 mV; Qmax 30.4 +/- 4.7 nC/micro(F), V -44.4 mV, k 14.1 1) and depolarized states (VH 0 50.0 6.7 -109.1 26.6 2) had properties as reported earlier. Linear capacitance (LC) increased by 8.8 4.0% compared with that fibers. Using control pulses to calculate 1, minor change dependence (to -44.6 mV 14.5 mV) small increase maximal 31.4 5.5 nC/micro(F] were observed. While most cases 1 transients seemed decay exponential time course, 2 currents showed characteristic biexponential behavior at membrane potentials between -90 -180 mV. The rate constant slower component fitted simple field diffusion model (alpha m 28.7 s-1, -124.0 15.6 mV). midpoint (V) similar obtained from Q-V fit 2, while steepness factor (k) resembled 1. This slow could also be isolated using stepped OFF protocol; is, hyperpolarizing -190 for 200 ms then coming back two steps. faster identified an ionic current insensitive 20 mM Co2+ but blocked large pulses. These findings are consistent implying interconvert when holding potential is changed. They explain difference previously found comparing factors 2.