title: Ion transport in rat proximal colon in vivo.
abstract: Active Na+ absorption by the rat proximal colon in vivo is for the most part electrically silent. The rheogenic Na+ flux makes up only 8%. To elucidate the underlying transport pathways, the following experimental approaches were used: ion substitution experiments such as choline for Na+, cyclamate for Cl-, variation of luminal pH; administration of known inhibitors; and determination of changes in luminal CO2 tension and pH. The transcolonic ion fluxes as well as the electrical parameters potential difference, specific electrical resistance, and short-circuit current were monitored. Na+ transport was drastically reduced in the absence of luminal Cl-, and vice versa Cl- absorption was blocked at zero Na+. NaCl absorption was blocked by amiloride (10(-3) M) and 4-acetamido-4'-isothiocyanostilbene-2, 2'-disulfonic acid and was lowered by acetazolamide. Colonic NaCl absorption was not influenced by luminal furosemide. Na+ absorption increased with alkalinization of the luminal fluid. Tris instead of HCO-3 buffer at constant pH favored Cl- uptake. The results may easily be explained by the operation of a Na+-H+ antiport functionally coupled to a Cl(-)-HCO-3 antiport. These transport processes are supposed to be present in the columnar cells of the colonic epithelium. There is good evidence for the association of K+ secretion with rheogenic Cl- secretion by the crypt cells.
mesh_terms: D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000086:Acetazolamide / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000666:Amphotericin B / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001693:Biological Transport, Active; D002712:Chlorides / Q000378:metabolism; D003106:Colon / Q000378:metabolism* / Q000502:physiology; D004553:Electric Conductivity; D005665:Furosemide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D013806:Theophylline / Q000494:pharmacology
chemical_list: D001639:Bicarbonates; D002712:Chlorides; D007473:Ion Channels; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D005665:Furosemide; D000666:Amphotericin B; D012964:Sodium; D013806:Theophylline; D000086:Acetazolamide; D011188:Potassium