Single chloride channels in colon mucosa and isolated colonic enterocytes of the rat

Chloride channels from rat colonic enterocytes were studied using the patch-clamp technique. After removal of mucus, inside-out patches were excised from the apical membrane of intact epithelium located at the luminal surface. They contained spontaneously switching Cl- channels with a conductance of 35-40 pS. The channels were blocked reversibly by anthracene-9-carboxylic acid (1mM). In excised patches from single enterocytes, isolated by calcium removal, the Cl- channels were studied in more detail. The I-V relation was linear between +/- 80 mV. The selectivity was I- greater than Br- greater than Cl- = NO3- greater than F- = HCO3-. Thirty pS Cl- channels were also found on the basolateral membrane of crypts isolated by brief calcium removal. The I-V curve of these Cl- channels was also linear. The results provide direct evidence for the existence of Cl- channels in the apical membrane of surface cells in colonic mucosa. The properties of these channels are similar to those previously observed when incorporating membrane vesicles into planar lipid bilayers. Both results support the validity of the theoretical models describing intestinal secretion.