title: Active NaCl absorption across posterior gills of hyperosmoregulating Chasmagnathus granulatus.
abstract: Split lamellae of posterior gills of Chasmagnathus granulatus adapted to 2.5 per thousand 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 micro A 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 BaCl(2) or furosemide) inhibited the negative I(sc) without affecting G(te). Addition of ouabain, BaCl(2) 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(-)/HCO(3)(-)-antiports.
authors.affiliation: 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. onkenh@ffclrp.usp.br
authors.forename: Horst
authors.initials: H
authors.lastname: Onken
authors.forename: Martin
authors.initials: M
authors.lastname: Tresguerres
authors.forename: Carlos M
authors.initials: CM
authors.lastname: Luquet
mesh_terms: D000042:Absorption; D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active; D003386:Brachyura / Q000378:metabolism* / Q000502:physiology; D004594:Electrophysiology; D005880:Gills / Q000378:metabolism* / Q000502:physiology; D017136:Ion Transport; D010042:Ouabain / Q000494:pharmacology; D012965:Sodium Chloride / Q000493:pharmacokinetics*; D014882:Water-Electrolyte Balance / Q000502:physiology*; D062367:ortho-Aminobenzoates / Q000494:pharmacology
chemical_list: D062367:ortho-Aminobenzoates; D012965:Sodium Chloride; D010042:Ouabain; C001209:fenamic acid; D000086:Acetazolamide