AJP - Gastrointestinal and Liver Physiology, Vol 258, Issue 6 825-G832, Copyright © 1990 by American Physiological Society
Base secretion in rat distal colon: ionic requirements
G. M. Feldman, J. D. Koethe and R. L. Stephenson
Department of Medicine, Veterans Administration Medical Center, Philadelphia, Pennsylvania.
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-.
