Active NaCl absorption across posterior gills of hyperosmoregulating Chasmagnathus granulatus

摘要

Split lamellae of posterior gills of Chasmagnathus granulatus adapted to 2.5%v salinity were mounted in a modified Ussing chamber. With NaCl-saline on both sides of the preparation a transepithelial voltage (V-te) of 4.1+/-0.5 mV (outside positive) was measured. After voltage-clamping, the negative short-circuit current (I-sc) amounted to -142+/-21 muA cm(-2) at a conductance (G(te)) of 44+/-5 mS cm(-2). Substitution of either chloride (by nitrate) or sodium (by choline) on both sides of split gill lamellae significantly reduced I-sc (by 70-80 %) and G(te) (by 30-50%). External CsCl (but not BaCl2 or furosemide) inhibited the negative I-sc without affecting G(te). Addition of ouabain, BaCl2 or diphenylamine-2-carboxylate to the internal bath inhibited I-sc at unchanged G(te). Internal acetazolamide did not affect I-sc or G(te) across split gill lamellae. Unidirectional Na+ influx across isolated and perfused posterior gills, however, was reduced by internal acetazolamide by approximately 20% at constant V-te. The results suggest that posterior gills of hyperosmoregulating C granulatus display a high conductance epithelium that actively absorbs NaCl in a coupled way by an electrogenic mechanism similar to that seen in the thick ascending limb of Henle's loop and, to a minor degree, by an electroneutral mechanism, presumably via apical Na+/H+-and Cl-/HCO3--antiports. [References: 31]