The isolated colonic mucosa from adult hens has been studied in vitro under short-circuit conditions. Colonic mucosa was prepared from hens fed either a NaCl-poor or a NaCl-rich diet. 2. The unidirectional transmucosal fluxes of chloride, K and Na were measured. For the high NaCl colon the fluxes of lysine were also measured. The effects of galactose, glucose, leucine, lysine, amiloride (10(-4) M) and acetazolamide (5 X 10(-4) M) on the short-circuit current (Isc) were examined. 3. The Isc of the high NaCl colon was stimulated by galactose, glucose, leucine and lysine in a manner which suggests that these substances were transported by the epithelium in co-transport with Na. The Isc was in most cases insensitive to amiloride (mucosal side), but moderately stimulated by acetazolamide (serosal side). The Isc was closely matched by the sum of the net transmucosal fluxes of chloride, lysine, K and Na. The effects of galactose, leucine and lysine on the Isc were maintained only when glucose was present on the serosal side of the preparations. 4. The Isc of the low NaCl colon depended on the presence of glucose on the serosal (or mucosal) side. It was not stimulated by galactose or by lysine, but leucine did stimulate when added to the mucosal solution. Adding amiloride on the mucosal side invariably eliminated or, in most cases, led to an inversion of the Isc. Acetazolamide markedly stimulated the Isc; and, when added after amiloride, acetazolamide caused the Isc to become positive again. The data on Isc and net fluxes of chloride, lysine, K and Na are consistent with the presence of a process of bicarbonate absorption or H ion secretion. 5. There is a net secretion of K across both the high and the low Na colon, which is highest in the former although both Isc and net absorption of Na are highest in the latter. 6. The results from both types of colon suggest that the transport of chloride differs with the functional status of tissues.
