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The Journal of Experimental Biology 206, 1017-1023 (2003)
doi: 10.1242/jeb.00227

Active NaCl absorption across posterior gills of hyperosmoregulating Chasmagnathus granulatus

Horst Onken^1,*, Martin Tresguerres² and Carlos M. Luquet²

¹ Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Avenida Bandeirantes 3900, Ribeirão Preto 14040-901, SP, Brasil
² Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pab. II, Ciudad Universitaria, C1428EHA Buenos Aires, Argentina

^* Author for correspondence (e-mail: onkenh{at}ffclrp.usp.br)

Accepted 10 January 2003

Split lamellae of posterior gills of Chasmagnathus granulatus adapted to 2.5 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 µA 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.

Key words: Chasmagnathus granulatus, Crustacea, crab gill, flux measurement, ion transport, osmoregulation, short-circuit current, transepithelial conductance, ion substitution, inhibitor, Ussing chamber

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