Localization of chloride secretion in rabbit colon: inhibition by anthracene-9-carboxylic acid

The substituted aromatic compound anthracene-9-carboxylic acid (A-9-C) was used to inhibit active Cl- secretion by the epithelium of short-circuited rabbit distal colon. Tissues were mounted in Ussing chambers and stimulated to secrete Cl- by the addition of 1 mM dibutyryl adenosine 3',5'-cyclic monophosphate to the serosal bath. Results of 36Cl-flux measurements showed that the addition of 0.1 mM A-9-C to the mucosal bath inhibited Cl- secretion by 48%. The site of Cl- secretion was determined by using conventional micro-electrodes to show that the cells of the crypt regions, and not the surface epithelial cells, responded to A-9-C by an increase in apical membrane fractional resistance from 0.75 to 0.80 and a hyperpolarization of the apical membrane from -64 to -68 mV (P less than 0.05). The sulfhydryl reagent dithiothreitol was added to the mucosal tissue bath to remove the mucus produced by goblet cells of the crypt regions of these tissues. The time for maximal inhibition of Cl- secretion by A-9-C was decreased from 30 to 15 min by removal of the mucus barrier. The effects of A-9-C on the crypt cells, as well as the effect of mucus on the inhibitory action of this compound, demonstrate that the crypt region is the site of Cl- secretion.