A transient sodium-hydrogen exchange system induced by catecholamines in erythrocytes of rainbow trout, Salmo gairdneri.

The addition of isoprenaline to an isotonic suspension of red blood cells of rainbow trout induces an amiloride-sensitive Na+ transport which is independent of Cl- and insensitive to 4,4'-diisothiocyano-2,2'-stilbene disulphonic acid (DIDS) and furosemide. Na+ uptake is accompanied by amiloride-sensitive H+ release. The H+ efflux is dependent upon the external Na+ concentration, the K0.5 value for Na+ being 16 mM. In the presence of DIDS, when the coupled NaCl entry (NaCl co-transport) induced by catecholamine is blocked, the results provide evidence for a linked movement of Na+ and H+, with a stoicheiometry of 1:1. Exchange of H+ for Na+ induces osmotic swelling of the cells which is due to the replacement of a bound proton by an osmotically active Na+ cation. In the absence of DIDS when the bulk of the Na+ uptake is the result of a coupled entry of Na+ and Cl-, H+ extrusion still occurs and the magnitude of acid excretion is identical to that found in DIDS-treated cells. This suggests that Na+-H+ exchange remains active. Addition of isoprenaline first stimulates the Na+-H+ exchange but only transiently. This is followed by a more permanent stimulation of the NaCl co-transport.