SALINITY DEPENDENCE OF NA+ H+ EXCHANGE ACTIVITY IN THE EEL (ANGUILLA-ANGUILLA) RENAL BRUSH-BORDER MEMBRANE-VESICLES/

The Na+/H+ antiporter activity present in eel kidney brush border memb rane vesicles prepared from sea-water and freshwater-adapted eels was monitored using the absorbance quenching of the weak base acridine ora nge. It was found that the activity of this renal antiporter, higher i n sea-water-adapted animals, was inhibited by dimethylamiloride. Compl ete adaptation in freshwater is reached after 5 days and seems specifi cally related to the transepithelial Na+ transport, as demonstrated by the parallel specific decrease of the activities of the brush border Na+/H+ exchanger and the basolateral located Na+/K+ ATPase. Kinetic pa rameter measurements (J(max) and K-m) indicate that the salinity adapt ation of this teleost occurs by a J(max) regulation of the antiporter.