title: A pharmacological examination of Na+ and Cl- transport in two species of freshwater fish.
abstract: We examined branchial Na(+) and Cl(-) uptake in two species of stenohaline, freshwater fish (goldfish and the Amazonian neon tetra). Kinetic analysis revealed that the two species had similar uptake capacities and affinities for Na(+) and Cl(-). However, while uptakes of Na(+) and Cl(-) (JNain and JClin, respectively) by goldfish were completely inhibited at pH 4.5 and below, uptake in tetras was unaffected by pH down to 3.25. Examination of Cl(-) transport with blockers indicated that goldfish and neon tetras utilize Cl(-)/HCO-3 exchange; SITS and SCN(-) inhibited Cl(-) uptake in both species. In contrast, large differences in Na(+) transport were indicated between the species. In goldfish, exposure to four Na(+)/H(+) exchange blockers, as well as the Na(+) channel blocker phenamil, strongly inhibited JNain. Further, Na(+) and Cl(-) uptake were strongly inhibited by the Na(+)/K(+)/Cl(-) cotransport inhibitor furosemide, as was JNain in "Cl(-)-free" water and JClin in "Na(+)-free" water. This suggests the presence of multiple transporters and possibly even a direct linkage between the transport of Na(+) and Cl(-) in goldfish. In contrast, none of these drugs strongly reduced Na(+) transport in neon tetras, which raises the possibility of a significantly different Na(+) transport mechanism in this acid-tolerant species.
authors.affiliation: Department of Biology, University of Miami, Coral Gables, FL 33157, USA. mpreest@jsd.claremont.edu
authors.forename: Marion R
authors.initials: MR
authors.lastname: Preest
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Gonzalez
authors.forename: Rod W
authors.initials: RW
authors.lastname: Wilson
mesh_terms: D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002712:Chlorides / Q000493:pharmacokinetics*; D004121:Dimethyl Sulfoxide; D005399:Fishes / Q000378:metabolism*; D005665:Furosemide / Q000494:pharmacology; D005880:Gills / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D012964:Sodium / Q000493:pharmacokinetics*; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D017923:Sodium-Hydrogen Exchangers; C047088:phenylamil; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D005665:Furosemide; D012964:Sodium; D004121:Dimethyl Sulfoxide