Ouabain-sensitive bicarbonate secretion and acid absorption by the marine teleost fish intestine play a role in osmoregulation

M. Grosell, J. Genz

Research output: Contribution to journalArticlepeer-review

81 Scopus citations


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 HCO 3- secretion rates measured by pH-stat techniques in Ussing chambers rely on oxidative energy metabolism and are highly temperature sensitive. At 25°C under in vivo-like conditions, secretion rates averaged 0.45 μmol·cm-2·h-1, of which 0.25 μmol·cm-2·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.

Original languageEnglish (US)
Pages (from-to)R1145-R1156
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Issue number4
StatePublished - 2006


  • Bicarbonate transport
  • Chloride absorption
  • Epithelial water transport
  • pH-stat titrations
  • Seawater ingestion

ASJC Scopus subject areas

  • Physiology


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