Active NaCl absorption across split lamellae of posterior gills of Chinesecrabs (Eriocheir sinensis) adapted to different salinities

Split lamellae of posterior gills of Eriocheir sinensis adapted to fresh wa ter, brackish waters (9 or 18 parts per thousand) or seawater (36 parts per thousand) were mounted in Ussing chambers, and transepithelial short-circu it currents and conductances were measured with salines, containing approxi mately in vivo-like NaCl concentrations. Active sodium and chloride absorpt ion (I-Na and I-CI),I- the transcellular conductances and the leak conducta nce were identified with external amiloride and/or DIDS. Split gill lamella e of crabs adapted to fresh water displayed similar magnitudes of I-Na and I-CI with 10 mmol 1(-1) NaCI in the external medium (internally haemolymph- like NaCl saline). Augmenting external NaCI (50 mmol 1(-1)) resulted in an increase of I-CI, whereas I-Na decreased. Split gill lamellae of crabs adap ted to brackish waters (external NaCI of 125 and 225 mmol 1(-1), respective ly) showed lower currents than preparations of freshwater crabs (50 mmol 1( -1) external NaCI). With split gill lamellae of seawater crabs no currents were detected (450 mmol 1(-1) NaCI on both sides). The transcellular conduc tances showed similar changes as the currents. The leak conductance of spli t gill lamellae of crabs adapted to fresh or brackish waters was low (0.3-0 .8 mS cm(-2)), whereas it was much higher (7 mS cm-2) with preparations of seawater crabs. (C) 1999 Elsevier Science Inc. All rights reserved.