Distribution of potassium and chloride permeability over the surface and T-tubule membranes of mammalian skeletal muscle
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- Dulhunty, A.F. J. Membrain Biol. (1979) 45: 293. doi:10.1007/BF01869290
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The distribution of K and Cl permeability,PK andPCl, over the surface and T-tubule membranes of red rat sternomastoid fibers has been determined. Membrane potential,Vm, was recorded with 3-m KCl-filled glass microelectrodes. Changes inVm with changes in [K]o or [Cl]o were used to estimatePCl/PK in normal and detubulated preparations. The results show that the T-tubule membrane has a highPCl and is therefore different from the T-tubule membrane of amphibian fibers. Analysis of the time course of depolarization when [K]o was raised (in SO4 solutions) showed thatPK was distributed over the surface and T-tubule membranes. Two observations suggested that T-tubulePCl was higher than the surfacePCl. Firstly, in normal fibers, the depolarization caused by an increase in [K]o was 3.5 times greater in SO4 solutions than in Cl solutions. In marked contrast, the depolarization in glycerol-treated fibers was independent of [Cl]o. Secondly, the rapid change inVm when [Cl]o was changed was reduced by 80% after glycerol treatment. Both observations suggest thatPCl was low in glycerol-treated fibers.PCl/PK was calculated from theVm data using Goldman, Hodgkin and Katz equations for Na and K or for Na, K, and Cl. In normal fibersPCl/PK=4.5 and in glycerol-treated fibersPCl/PK=0.28. Since it is unlikely that glycerol treatment would increasePK, the reduction in the ratio must follow the loss of Cl permeability “channels” in the T-tubule membrane.