Control of red cell volume and pH in trout: Effects of isoproterenol, transport inhibitors, and extracellular pH in bicarbonate/carbon dioxide‐buffered media

Abstract

AbstractThe effects of extracellular pH and beta‐adrenergic stimula‐tion on the volume and pH of rainbow. trout red cells were studied in HCO3−/ CO2 butfered media. A decrease in extracellular pH caused an increase in red cell volume and a decrease in intracellular pH. The pH‐induced changes in cell volume were inhibited by 4,4′‐Diisothiocyanostilbene‐2,2′‐Disulfonic acid, (DIDS), an inhibitor of the anion exchange pathway, but not by amiloride, an inhibitor of Na+/H+ exchange, indicating that these volume changes are mainly associated with movements of chloride across the red cell membrane, and that the Na+/H+ exchanger is not activated by changes in intracellular pH alone. The adrenergic drug, isoproterenol, promoted cell swelling and proton extrusion even in the presence of 10 mM HCO3−, showing that the adrenergic response plays a significant role in the control of cytoplasmic pH. These responses were enhanced by a decrease in extracellular pH, showing that the adrenergic response is of benefit to stressed animals. DIDS markedly enhanced the effect of isoproterenol on the pHi, but abolished the increase in red cell volume. The effects of furosemide were similar to those of DIDS, suggesting that these transport inhibitors have a similar mode of action. Amiloride, on the other hand, inhibited both the volume and the pH changes associated with adrenergic stimulation. These observations support the double Na+/H+ and HCO3−/CI− exchange model of adrenergic swelling in fish red cells.