Abstract
T-system action potentials were recorded optically from intact frog skeletal muscle fibers stained with the non-penetrating potentiometric dye NK-2367. The effect of chloride removal on the falling phase of the radially propagating tubular action potential was studied to determine whether a chloride conductance located in the T-system membranes contributes to tubular repolarization during activity. Our results show that, in chloride-free Ringer, repolarization of the tubular action potential is significantly slowed. Moreover, the late phase of tubular repolarization is characterized by a large afterpotential, which is highly temperature-dependent and appears as a secondary peak above 10° C. The optical data were compared with predicted T-system action potentials generated from a radial cable equivalent circuit model of the T-system, in which the effects of a distributed tubular leak conductance were tested. Results of this analysis are consistent with the proposal that some of the outward repolarization current during the T-system action potential is drawn across a chloride conductance located in the T-system membranes.
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Heiny, J.A., Valle, J.R. & Bryant, S.H. Optical evidence for a chloride conductance in the T-system of frog skeletal muscle. Pflügers Arch 416, 288–295 (1990). https://doi.org/10.1007/BF00392065
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DOI: https://doi.org/10.1007/BF00392065