Na FLUXES ACROSS ISOLATED PERFUSED GILLS OF THE CHINESE CRAB ERIOCHEIR SINENSIS

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 counterbalances 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 paiis 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.