CL- INFLUX ACROSS POSTERIOR GILLS OF THE CHINESE CRAB (ERIOCHEIR-SINENSIS) - POTENTIAL ENERGIZATION BY A V-TYPE H-ATPASE()

Cl- absorption across isolated, perfused gills of freshwater adapted C hinese crabs (Eriocheir sinensis) was analysed by measuring transepith elial potential differences (PDte) and radioactive tracer fluxes acros s isolated, perfused posterior gills. Applying hemolymph-like NaCl sal ines 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 mu mol . hr(-1). g(-1) wet weight (ww) (n=14) resulted in a Cl- net influ x of 226+/-31 mu mol . hr(-1). g(-1) ww. Symmetrical substitution of N a+ 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. Neverth eless, 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 unchang ed. Following external application of 1 mu mol/l of the V-type H+-ATPa se inhibitor bafilomycin, A(I) PDte and Cl- efffuxes were not signific antly affected. However, Cl- influxes decreased. These findings sugges t that Cl- can be taken up independently of Na+ and that active Naf in dependent Cl- uptake across the posterior gill of Eriocheir sinensis i s probably driven by a V-type H+-ATPase localized in the apical membra ne.