Modulation of K-Cl Cotransport in Volume-Clamped Low-K Sheep Erythrocytes by pH, Magnesium, and ATP

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Article

Publication Date

10-1-1996

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Abstract

Cellular pH, ionized Mg (Mgi2+), and MgATP concentration of red blood cells, concomitantly with cell volume, change transiently during circulation. The action of these three effectors on Cl-dependent K efflux was examined in low-K sheep red blood cells with constant cell volume. Activation of K-Cl efflux by Mgi2+ extraction required ATP, suggesting that phosphorylation of a putative component occurred before Mgi2+ extraction. Conversely, Mg and ATP were synergistic inhibitors of K-Cl cotransport, since maximal inhibition was observed only in cells containing both ATP and > 300 microM Mgi2+. Both findings suggest dual roles for Mg and ATP. At 300-600 microM Mgi2+, lowering the pH from approximately 7.4 to approximately 6.5 stimulated K-Cl efflux only in fed cells, suggesting that protons oppose or release the inhibition by Mgi2+ and ATP. A direct effect of both protons and Mgi2+ on the cotransporter is suggested by their inhibition of K-Cl efflux in ATP-depleted cells. These findings are discussed in light of the current phosphorylation/dephosphorylation hypothesis.

DOI

10.1152/ajpcell.1996.271.4.c1049

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