title: Unidirectional flux ratio for potassium ions in depolarized frog skeletal muscle.
abstract: Small bundles of frog skeletal muscle fibers were loaded with 305 mM K+ and 120 mM Cl-, and 42K+ tracer efflux and influx were measured as a function of external K+ concentration ([K+]o) at a resting potential of -2 mV. As [K+]o was lowered from 305 mM, efflux decreased along a markedly sigmoidal curve, reaching a constant nonzero value at low [K+]o. Influx varied linearly with [K+]o at low [K+]o and more steeply at higher [K+]o. The ratio of influx to efflux was described by the equation: influx/efflux = exp[-n(V - VK)F/RT] with n = 2 at high [K+]o, but the ratio approached this equation with n = 1 at low [K+]o. Efflux did not depend on [K+]o when the membrane potential was raised to +36 mV, whereas at low [K+]o decreasing the membrane potential to -19 mV further activated the efflux. The results are discussed in terms of an inwardly rectifying potassium channel with two or more activating sites within the membrane that bind K+ and are accessible from the external solution.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011894:Rana pipiens; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D013779:Tetrodotoxin; D010042:Ouabain; D011188:Potassium