title: Ouabain-sensitive bicarbonate secretion and acid absorption by the marine teleost fish intestine play a role in osmoregulation.
abstract: The gulf toadfish (Opsanus beta) intestine secretes base mainly in the form of HCO3- via apical anion exchange to serve Cl- and water absorption for osmoregulatory purposes. Luminal HCO3- secretion rates measured by pH-stat techniques in Ussing chambers rely on oxidative energy metabolism and are highly temperature sensitive. At 25 degrees C under in vivo-like conditions, secretion rates averaged 0.45 micromol x cm(-2) x h(-1), of which 0.25 micromol x cm(-2) x h(-1) can be accounted for by hydration of endogenous CO2 partly catalyzed by carbonic anhydrase. Complete polarity of secretion of HCO3- and H+ arising from the CO2 hydration reaction is evident from equal rates of luminal HCO3- secretion via anion exchange and basolateral H+ extrusion. When basolateral H+ extrusion is partly inhibited by reduction of serosal pH, luminal HCO3- secretion is reduced. Basolateral H+ secretion occurs in exchange for Na+ via an ethylisopropylamiloride-insensitive mechanism and is ultimately fueled by the activity of the basolateral Na+-K+-ATPase. Fluid absorption by the toadfish intestine to oppose diffusive water loss to the concentrated marine environment is accompanied by a substantial basolateral H+ extrusion, intimately linking osmoregulation and acid-base balance.
authors.affiliation: Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149-1098, USA. mgrosell@rsmas.miami.edu
authors.forename: M
authors.initials: M
authors.lastname: Grosell
authors.forename: J
authors.initials: J
authors.lastname: Genz
mesh_terms: D000143:Acids / Q000493:pharmacokinetics; D000818:Animals; D024541:Batrachoidiformes / Q000502:physiology*; D001639:Bicarbonates / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007408:Intestinal Absorption / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011522:Protons; D012623:Seawater; D012964:Sodium / Q000378:metabolism; D012965:Sodium Chloride / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D000143:Acids; D001639:Bicarbonates; D004791:Enzyme Inhibitors; D011522:Protons; D002245:Carbon Dioxide; D012965:Sodium Chloride; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase