title: Bicarbonate secretion in rat distal colon in vitro: a measurement technique.
abstract: To study HCO3- secretion in rat distal colon, we utilized a technique that permits control of electrical and chemical transepithelial gradients. With symmetrical solutions (pH 7.4, [HCO3-] 25 mM, and CO2 tension 40 mmHg) bathing both tissue surfaces and under short-circuit conditions, HCO3- secretion remained stable for greater than 4 h at 1 mueq. h-1.cm-2. As the mucosal solution was alkalinized, the serosal solution was acidified at 3.1 mueq.h-1.cm-2. Ninety-four percent of serosal acidification was accounted for by the rate of metabolic lactic acid generation and transepithelial HCO3- secretion. Clamping transepithelial voltage reversibly affected net HCO3- secretion, and a linear relationship existed between clamped mucosal voltage and net HCO3- flux (r = 0.99); mucosal voltage of -68 mV completely inhibited net secretion. The apparent permeability coefficient of the colon to HCO3- is 2.8 X 10(-6) cm/s. One millimolar ouabain completely inhibited net HCO3- secretion. Acetazolamide (10(-4) M) inhibited secretion by approximately 50%, whereas a 10(-3) M concentration inhibited secretion by 90%. These data demonstrate that net colonic HCO3- secretion can be measured without imposed electrical and chemical gradients and that this flux is voltage sensitive and depends on carbonic anhydrase and Na+-K+-ATPase activities.
authors.affiliation: Department of Medicine, Veterans Administration Medical Center, Philadelphia, Pennsylvania.
authors.forename: G M
authors.initials: GM
authors.lastname: Feldman
authors.forename: S F
authors.initials: SF
authors.lastname: Berman
authors.forename: R L
authors.initials: RL
authors.lastname: Stephenson
mesh_terms: D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D003106:Colon / Q000201:enzymology / Q000378:metabolism* / Q000502:physiology; D004594:Electrophysiology; D004848:Epithelium / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008722:Methods; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
chemical_list: D001639:Bicarbonates; D002257:Carbonic Anhydrase Inhibitors; D010042:Ouabain; D000086:Acetazolamide