title: Bicarbonate absorption by in vitro amphibian small intestine.
abstract: Isolated segments of jejunum from Amphiuma bathed in Cl--free (SO42(-)) media usually generated serosa-negative electrical potentials when HCO3(-) was present in the media. Bidirectional isotope fluxes under short circuit revealed a negligible absorption of Na+ and a residual flux consistent with anion absorption. Acetazolamide (10(-4) M) eliminated the short-circuit current and the residual flux. Segments of jejunum exposed on the mucosal surface to HCO3(-) (pH 7.4) alkalinized the unbuffered serosal fluid at a rate of about 1.1 mueq . h-1 . cm-2, as measured by the pH-stat while clamped at zero transepithelial potential. Acetazolamide, anoxia, and 2,4-dinitrophenol lowered the rate of alkalinization and simultaneously reduced the short-circuit current by an equal amount. Absorption was constant above a [HCO3(-)] of 35 meq/l and uninfluenced by applied transepithelial voltage gradients. HCO3(-) absorption was not reduced after replacement of media Na+ or Cl- but was reduced on addition of ouabain or removal of K+. It is concluded that the jejunum actively absorbs HCO3(-) by an electrogenic process that does not involve Na+-H+ exchange.
mesh_terms: D000086:Acetazolamide / Q000494:pharmacology; D000663:Amphibians; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002712:Chlorides / Q000494:pharmacology; D004140:Dinitrophenols / Q000494:pharmacology; D004386:Duodenum / Q000502:physiology*; D004553:Electric Conductivity; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000502:physiology*; D007583:Jejunum / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D004140:Dinitrophenols; D010042:Ouabain; D000086:Acetazolamide