Intestinal bicarbonate secretion in Amphiuma measured by pH stat in vitro: relationship with metabolism and transport of sodium and chloride ions.
1. Isolated Amphiuma small intestine exposed on both surfaces to buffered or unbuffered media generated gradients of pH under short-circuited conditions consistent with secretion of HCO3(-). 2. When unbuffered mucosal medium was maintained at pH 7.4 by addition of acid, alkalinization of the mucosal medium occurred at a rate of 1-2 microequiv/hr cm2 under short-circuit conditions (Isc) and was reduced by anoxia, acetazolamide or removal of CO2. 3. The rate of HCO3(-) secretion (JHCO3(-)) was reduced at a mucosal pH above or below 7.4 and was proportional to serosal HCO3(-). 4. JHCO3(-) was reduced in Na+-free (choline) and Cl-free (SO4(2-) media and after exposure to the stilbene SITS. 5. The difference JHCO3(-)--Isc was consistent with net Cl- absorption. 6. The tissue resistance (Rt) was elevated upon exposure to serosal HCO3(-) and lowered by mucosal HCO3(-). 7. The intestinal mucosa exhibited carbonic anhydrase activity that was sensitive to ethoxazolamide. 8. It is concluded that HCO3(-) secretion is active, influenced by intracellular carbonic anhydrase activity and coupled to Cl- and possibly Na+ absorption.
D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D002712:Chlorides / Q000378:metabolism*; D004848:Epithelium / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000502:physiology; D007421:Intestine, Small / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D012964:Sodium / Q000378:metabolism*; D014562:Caudata / Q000378:metabolism*
D001639:Bicarbonates; D002712:Chlorides; D012964:Sodium