Cl− influx across posterior gills of the Chinese crab (Eriocheir sinensis): potential energization by a V-type H+-ATPase

Abstract

Abstract Cl− absorption across isolated, perfused gills of freshwater adapted Chinese crabs (Eriocheir sinensis) was analysed by measuring transepithelial potential differences (PDte) and radioactive tracer fluxes across isolated, perfused posterior gills. Applying hemolymph-like NaCl salines on both sides of the epithelium PDte amounted to −30±1 mV (n=14). Undirectional Cl− influxes of 470±38 and effluxes of 245±27 μmol·hr−1·g−1 wet weight (ww) (n=14) resulted in a Cl− net influx of 226±31 μmol·hr−1·g−1 ww. Symmetrical substitution of Na+ by choline resulted in a substantial hyperpolarisation of the gill. Cl− influx was unchanged under these conditions. However, net influx of Cl− decreased by 40%, due to an increase of the Cl− efflux. Nevertheless, a significant Cl− net influx remained which was independent of the presence of Na+. When 2 mmol/l ouabain were added to the internal perfusion medium, PDte increased, although the fluxes remained unchanged. Following external application of 1μmol/l of the V-type H+-ATPase inhibitor bafilomycin, Al PDte and Cl− effluxes were not significantly affected. However, Cl− influxes decreased. These findings suggest that Cl− can be taken up independently of Na+ and that active Na+ independent Cl− uptake across the posterior gill of Eriocheir sinensis is probably driven by a V-type H+-ATPase localized in the apical membrane.