Optical evidence for a chloride conductance in the T-system of frog skeletal muscle.
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 after-potential, which is highly temperature-dependent and appears as a secondary peak above 10 degrees 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.
Heiny
J A
JA
Department of Physiology and Biophysics, University of Cincinnati College of Medicine, OH 45267-0576.
Valle
J R
JR
Bryant
S H
SH
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002712:Chlorides / Q000493:pharmacokinetics / Q000502:physiology*; D004553:Electric Conductivity / Q000187:drug effects / Q000502:physiology*; D009132:Muscles / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D011894:Rana pipiens / Q000502:physiology*; D013696:Temperature
D002712:Chlorides