Regulation of acid and ion transfer across the membrane of nucleated erythrocytes

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Abstract
The major pathways for proton transport across the membrane of nucleated erythrocytes are the passive Jacobs–Stewart cycle and the secondarily active sodium–proton exchange. The relative importance of these two pathways in the control of red cell pH depends on the sodium–proton exchange rate and the rate of the slowest step of passive proton equilibration. In cyclostome red cells, which lack anion exchange, intracellular pH is controlled by the sodium-dependent acid–extrusion mechanism. In unstimulated teleost red cells, the Jacobs–Stewart cycle appears to be the most important pathway for the transport of protons across the membrane. Adrenergic stimulation activates sodium–proton exchange. Sodium–proton exchange is able to increase intracellular pH and decrease extracellular pH because the rate of proton transport via the Jacobs–Stewart cycle is limited by the uncatalysed extracellular dehydration of carbonic acid to carbon dioxide. The turnover rate of the adrenergically activated sodium–proton exchange is influenced by pH and oxygen tension. In amphibian red cells, acidification activates sodium–proton exchange. The exchange may limit the changes in intracellular pH after acid–base disturbances.

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