title: Base secretion in rat distal colon: ionic requirements.
abstract: To evaluate the ionic requirements of colonic base secretion, segments of rat distal colon were studied under short-circuited conditions. Net base flux was composed of an active secretory component and a diffusive component. Studied in the absence of a transepithelial HCO3- concentration gradient, active base secretion was dependent on the HCO3- concentration of the bathing solution but was not influenced by the CO2 tension or pH. Base secretion appeared to saturate with a Km of 33 +/- 9 mM and was inhibited by ouabain. The diffusive component was characterized by an apparent permeability coefficient to HCO3- of 8.9 +/- 0.9 x 10(-6) cm/s. In addition to requiring HCO3- on the serosal surface, net base secretion was inhibited by reducing the Na+ concentration in the serosal medium and the Cl- concentration in the mucosal medium. These data suggest that colonic base secretion involves HCO3- entry across the basolateral surface, energized by the Na+ gradient, and HCO3- exit across the apical surface in exchange for Cl-.
authors.affiliation: Department of Medicine, Veterans Administration Medical Center, Philadelphia, Pennsylvania.
authors.forename: G M
authors.initials: GM
authors.lastname: Feldman
authors.forename: J D
authors.initials: JD
authors.lastname: Koethe
authors.forename: R L
authors.initials: RL
authors.lastname: Stephenson
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism* / Q000494:pharmacology; D002245:Carbon Dioxide / Q000494:pharmacology; D003106:Colon / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008297:Male; D009130:Muscle, Smooth / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001639:Bicarbonates; D002245:Carbon Dioxide; D010042:Ouabain