Mechanisms of transport of Na, Cl, and K in the human colon.

Ionic transport across isolated, stripped, human colonic mucosa was studied in vitro using a modified short circuit current technique. Electrical potential difference and short circuit current were dependent on the presence of sodium ions in the mucosal bathing solution and were unaffected by addition of 10 mM glucose to the solution. Ouabain (10(-3) M) added to the serosal reservoir abolished both potential difference and short circuit current. Isotopic flux measurements across short-circuited colonic mucosa showed a net active sodium absorption which accounted for the observed short circuit current and was unaffected by 10 mM glucose. Chloride was also actively absorbed and this was unaffected by removal of sodium from the bathing solutions. Ouabain abolished net sodium absorption but had no effect on chloride absorption. There was a net active secretion of potassium which was abolished in sodium-free buffer. We conclude that sodium is actively absorbed via a rheogenic process which is not stimulated by glucose; chloride is actively absorbed via a nonelectrogenic process, not linked to sodium transport, and probably involving a Cl-HCO3- exchange; and postassium is actively secreted possibly via a Na+K+ exchange.