Active NaCl absorption across posterior gills of Chasmagnathus granulatus.

ONKEN, H; TRESGUERRES, M; LUQUET, C.

JOURNAL OF EXPERIMENTAL BIOLOGY

The Company of Biologists

Lugar: Oxford; Año: 2003 vol. 206 p. 1017 - 1023

0022-0949

Split lamellae of posterior gills of Chasmagnathusgranulatus adapted to 2.5‰ salinity were mounted in amodified Ussing chamber. With NaCl-saline on both sidesof the preparation a transepithelial voltage (Vte) of4.1±0.5 mV (outside positive) was measured. After voltageclamping,the negative short-circuit current (Isc)amounted to –142±21 mAcm–2 at a conductance (Gte) of44±5mScm–2. Substitution of either chloride (by nitrate)or sodium (by choline) on both sides of split gill lamellaesignificantly reduced Isc (by 70–80%) and Gte (by30–50%). External CsCl (but not BaCl2 or furosemide)inhibited the negative Isc without affecting Gte. Addition ofouabain, BaCl2 or diphenylamine-2-carboxylate to theinternal bath inhibited Isc at unchanged Gte. Internalacetazolamide did not affect Isc or Gte across split gilllamellae. Unidirectional Na+ influx across isolated andperfused posterior gills, however, was reduced by internalacetazolamide by approximately 20% at constant Vte. Theresults suggest that posterior gills of hyperosmoregulatingC. granulatus display a high conductance epithelium thatactively absorbs NaCl in a coupled way by an electrogenicmechanism similar to that seen in the thick ascending limbof Henle’s loop and, to a minor degree, by anelectroneutral mechanism, presumably via apical Na+/H+-and Cl–/HCO3–-antiports.