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

Abstract

SUMMARY1. 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.2. Na+ uptake is accompanied by amiloride-sensitive H+ release. The H+ efflux is dependent upon the external Na+ concentration, the Ko.5 value for Na+ being 16 mm.3. 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 :1.4. 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.5. 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.6. Addition of isoprenaline first stimulates the Na+-H+ exchange but only transiently. This is followed by a more permanent stimulation ofthe NaCl co-transport.

Cloning and expression of a cAMP-activated Na+/H+ exchanger: evidence that the cytoplasmic domain mediates hormonal regulation.

“…It has been demonstrated in vitro (16,17) and also in vivo (30,31) that this antiporter is activated by catecholamines through increases in intracellular cAMP, which leads to stimulation of PKA. cAMP does not activate Na+/H+ exchange in other cells except in rat hepatocytes (40) and in another nucleated erythrocyte (frog red cell) (32).…”

“…It was of interest to consider the Na+/H+ exchanger found in nucleated trout red cells (termed f3NHE) since, in contradistinction to NHE1 and to the apical antiporter, it is activated by cAMP and other cAMP-dependent protein kinase (protein kinase A; PKA) activators such as catecholamines or forskolin (16)(17)(18)(19). Thus, it is likely to represent an additional form of antiporter.…”

Epidermal growth factor and cyclic AMP stimulate Na+/H+ exchange in isolated rat hepatocytes

“…Conversely, in some other systems cyclic AMP has been implicated in a similar stimulatory role to that described here. Catecholamines acting via P-receptors in trout erythrocytes have been shown to increase the activity of the system [34], and cyclic AMP is thought to be involved in the concavalin A activation of N a + / H + exchange in T lymphocytes [35].…”

Volume‐activated Cl(‐)‐independent and Cl(‐)‐dependent K+ pathways in trout red blood cells.

“…Conversely, the Cl--independent K+ loss observed in hypotonically swollen cells is expected to occur via another mechanism: an electroneutral K+-H+ exchange running in parallel with anion-OH-exchange, or an electrogenic K+ flux with Cl-or N03-in the role of electrical counter-ion. N03-is accepted both by the anion exchanger and by the anion conductance pathway in trout red cells (Baroin et al 1984 a). We will now examine these two K+ transport pathways in detail.…”