Na+ Fluxes Across Isolated Perfused Gills of the Chinese Crab Eriocheir Sinensis

Abstract

Sodium transport processes in the branchial epithelium of euryhaline crustaceans have been investigated using a perfused preparation of gills isolated from Chinese crabs Eriocheir sinensis acclimated to dilute (FW) and to concentrated (SW) media. The results clearly establish the existence of a functional difference between the different pairs of branchiae with respect to their participation in the regulation of the blood Na+ content. In FW-acclimated animals, the Na+ active uptake which counter-balances the salt loss along the concentration gradient is mostly achieved across the three posterior pairs of gills. Conversely, the Na+ fluxes measured in the three anterior pairs are essentially passive and carrier-mediated. Further characterization of the Na+ uptake system present in the posterior gills by means of inhibitors like ouabain and ethacrynic acid indicates the existence of at least two spatially separated components of the Na+ carrying system. It is shown that NH4+ may be used as co-ion for Na+ but that such a coupling can only account for a very small part of the Na+ actively transported inward. The existence of an electrogenic mechanism or of another coupled system has thus to be postulated but remains at present a matter of speculation. To study FW-to-SW and SW-to-FW acclimation, Na+ fluxes were measured in isolated gills of SW-acclimated crabs and of FW crabs perfused and incubated in SW conditions. During acclimation to SW the Na+ active uptake in the posterior gills is abolished primarily as a result of inhibition of the Na+ carrier activity.