Summary
The voltage dependence for outward-going current of the Ca-activated K+ conductance (g k (Ca)) of the human red cell membrane has been examined over a wide range of membrane potentials (V m) at constant values of [K+]ex, [K+]c and pHc, the intact cells being preloaded to different concentrations of ionized calcium. Outward-current conductances were calculated from initial net effluxes of K+ and the corresponding (V m-Ek) values. The basic conductance, defined as the outward-current coductance at (V m-Ek) ≥ 20 mV and [K+]ex ≥ 3mM (B. Vestergaard-Bogind, P. Stampe and P. Christophersen,J. Membrane Biol. 95:121–130, 1987) was found to be a function of cellular ionized Ca. At all degrees of Ca activationg K(Ca) was an apparently linear function of voltage (V m range −40 to +70 mV), the absolute level as well as the slope decreasing with decreasing activation. In a simple two-state model the constant voltage dependence can, at the different degrees of Ca activation, be accounted for by a Boltzmann-type equilibrium function with an equivalent valence of ∼0.4, assuming chemical equilibrium atV m=0 mV. Alternatively, the phenomenon might be explained by a voltage-dependent block of the outward current by an intracellular ion. Superimposed upon the basic conductance is the apparently independent inward-rectifying steep voltage function with an equivalent valence of ∼ 5 and chemical equilibrium at the givenE K value.
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Abbreviations
- CCCP:
-
carbonyl cyanidem-chlorophenylhydrazone
- DIDS:
-
4,4′-diisothiocyanostilbene-2,2′-disul
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Stampe, P., Vestergaard-Bogind, B. Ca2+-activated K+ conductance of human red cell membranes exhibits two different types of voltage dependence. J. Membrain Biol. 101, 165–172 (1988). https://doi.org/10.1007/BF01872831
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DOI: https://doi.org/10.1007/BF01872831