MUCOSAL ACIDIFICATION AND AN ACID MICROCLIMATE IN THE HEN COLON IN-VITRO

Experiments were performed on isolated, stripped colonic epithelia of low-salt-adapted hens (Gallus domesticus) in order to characterize aci d secretion by this tissue. With symmetric, weak buffer solutions, col onic epithelia acidified both mucosal and serosal sides. Titration mea surements of the mucosal acidification rate (pH-stat technique) averag ed 1.63 +/- 0.25 muEq . cm-2 . h-1. Mucosal acidification was also evi dent in colons from high-salt-adapted birds and in low-salt-adapted co prodeum, but was completely abolished in the high-salt coprodeum. Muco sal acidification by low-salt-adapted colonic epithelium was unaffecte d by sodium replacement, mucosal amiloride (10(-3) mol - l-1), and ser osal ouabain (5 x 10(-4) mol - l-1), although all three treatments sig nificantly reduced or reversed the short-circuit current. Acetazolamid e (10(-3) mol . l-1, serosal) reduced mucosal acidification by 15% and simultaneously increased short-circuit current by a similar amount. C olonic epithelia incubated in glucose-free solutions had significantly lower acidification rates (0.59 +/- 0.13 muEq . cm-2 . h-1, P < 0.002 versus controls) and addition of glucose (15 mmol . l-1), but not gal actose, partially restored acidification to control levels. Anoxia (N2 gassing) completely inhibited short-circuit current, but reduced acid ification by only 30%. A surface microclimate pH, nearly 2 pH units mo re acidic than the bath pH of 7.1-7.4, was measured in low-salt-adapte d colon and coprodeum. The acid microclimate of both tissues was parti ally attenuated by adaptation to a high-salt diet. Colonic microclimat e pH was dependent on the presence of glucose and sensitive to the bat h pH. Histochemical staining for carbonic anhydrase localized this enz yme to cytoplasm and lateral margins of one subfraction of colonic cel ls, and to cytoplasm in a second subpopulation. Intense staining was a lso evident in subepithelial capillaries. These results suggest that a large part of mucosal acidification and maintenance of the acid micro climate in hen colon may be dependent on glycolysis and metabolic acid production, although a smaller, electrogenic and acetazolamide-sensit ive component also appears to exist. This latter component may become more prominent under conditions of cellular acidification.