Effects of quinine on Ca++-induced K+ efflux from human red blood cells
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- Reichstein, E. & Rothstein, A. J. Membrain Biol. (1981) 59: 57. doi:10.1007/BF01870821
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The Ca++-mediated increase in K+-permeability of intact red blood cells (Gardos effect) was initiated by exposing cells to known concentrations of Ca++ (using EGTA buffers) in the presence of the ionophore A23187. The potency of quinine, an inhibitor of the response, was found to depend on the external K+ concentration. In K+-free solutions the concentration of quinine to achieve 50% inhibition (K50) was 5 μm, but at 5mm K+ the required concentration was increased 20-fold to 100 μm. An increase in internal Na+ had the opposite effect, allowing a high potency of quinine despite the presence of external K+. Alterations in the internal K+ level, on the other hand, were without effect on theK50, suggesting that the membrane potential is not a factor. This conclusion is supported by the lack of effect on quinine inhibition of substitution of Cl− by NO3−, a considerably more permeant anion. The data are consistent with the hypothesis that quinine inhibits by competitively displacing K+ from an external binding site, the reported K+-activation site for the Ca++-mediated K+-permeability.