We examined the effects of pH, internal ionized Ca (Ca2+ i ), cellular ATP, external divalent cations and quinine on Cl-independent ouabain-resistant K+ efflux in volume-clamped sheep red blood cells (SRBCs) of normal high (HK) and low (LK) intracellular K+ phenotypes. In LK SRBCs the K+ efflux was higher at pH 9.0 (350%) than at pHs 7.4 and 6.5, and was inhibited by external divalent cations, quinine, and cellular ATP depletion. The above findings suggest that the increased K+ efflux at alkaline pH is due to the opening of ion channels or specific transporters in the cell membrane. In addition, K+ efflux was activated (100%) when Ca2+ i was increased (+A23187, +Ca2+ o ) into the μm range. However, in comparison to human red blood cells, the Ca2+ i -induced increase in K+ efflux in LK SRBCs was fourfold smaller and insensitive to quinine and charybdotoxin. The Na+ efflux was also higher at pH 9.0 than at pH 7.4, and activated (about 40%) by increasing Ca2+ i . In contrast, in HK SRBCs the K+ efflux at pH 9.0 was neither inhibited by quinine nor activated by Ca2+ i . These studies suggest the presence in LK SRBCs, of at least two pathways for Cl−-independent K+ and Na+ transport, of which one is unmasked by alkalinization, and the other by a rise in Ca2+ i .
The Journal of Membrane Biology – Springer Journals
Published: Apr 1, 1997
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