title: Bicarbonate secretion plays a role in chloride and water absorption of the European flounder intestine.
abstract: Experiments performed on isolated intestinal segments from the marine teleost fish, the European flounder (Platichthys flesus), revealed that the intestinal epithelium is capable of secondary active HCO3(-) secretion in the order of 0.2-0.3 micromol x cm(-2) x h(-1) against apparent electrochemical gradient. The HCO3(-) secretion occurs via anion exchange, is dependent on mucosal Cl(-), results in very high mucosal HCO3(-) concentrations, and contributes significantly to Cl(-) and fluid absorption. This present study was conducted under in vivo-like conditions, with mucosal saline resembling intestinal fluids in vivo. These conditions result in a transepithelial potential of -16.2 mV (serosal side negative), which is very different from the -2.2 mV observed under symmetrical conditions. Under these conditions, we found a significant part of the HCO3(-) secretion is fueled by endogenous epithelial CO2 hydration mediated by carbonic anhydrase because acetazolamide (10(-4) M) was found to inhibit HCO3(-) secretion and removal of serosal CO(2) was found not to influence HCO3(-) secretion. Reversal of the epithelial electrochemical gradient for Cl(-) (removal of serosal Cl(-)) and elevation of serosal HCO3(-) resulted in enhanced HCO3(-) secretion and enhanced Cl(-) and fluid absorption. Cl(-) absorption via an anion exchange system appears to partly drive fluid absorption across the intestine in the absence of net Na(+) absorption.
authors.affiliation: RSMAS, Division of Marine Biology and Fisheries, 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: C M
authors.initials: CM
authors.lastname: Wood
authors.forename: R W
authors.initials: RW
authors.lastname: Wilson
authors.forename: N R
authors.initials: NR
authors.lastname: Bury
authors.forename: C
authors.initials: C
authors.lastname: Hogstrand
authors.forename: C
authors.initials: C
authors.lastname: Rankin
authors.forename: F B
authors.initials: FB
authors.lastname: Jensen
mesh_terms: D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D017920:Antiporters / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D004232:Diuretics / Q000494:pharmacology; D004563:Electrochemistry; D004848:Epithelium / Q000378:metabolism; D005432:Flounder / Q000378:metabolism*; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D014867:Water / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000502:physiology
chemical_list: D017920:Antiporters; D001639:Bicarbonates; D002257:Carbonic Anhydrase Inhibitors; D002712:Chlorides; D004232:Diuretics; D014867:Water; D002245:Carbon Dioxide; D002256:Carbonic Anhydrases; D000086:Acetazolamide