Alkaline pH and internal calcium increase Na+ and K+ effluxes in LK sheep red blood cells in Cl--free solutions

• Published in: The Journal of membrane biology Vol. 156; no. 3; pp. 287 - 295
• Main Authors: Ortiz-Carranza, O, Miller, M E, Adragna, N C, Lauf, P K
• Format: Journal Article
• Language: English
• Published: United States 01-04-1997
• Subjects: Adenosine Triphosphate - metabolism; Animals; Calcimycin - pharmacology; Calcium - physiology; Calcium Channel Blockers - pharmacology; Calcium Channels - drug effects; Calcium Channels - metabolism; Cations, Divalent - pharmacology; Charybdotoxin - pharmacology; Chlorides; Erythrocytes - metabolism; Humans; Hydrogen-Ion Concentration; Ion Transport - drug effects; Ionophores - pharmacology; Potassium - metabolism; Quinine - pharmacology; Sheep - blood; Sodium - metabolism
• ISSN: 0022-2631; 1432-1424
• DOI: 10.1007/s002329900208

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 microm 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.