Electrolyte absorption and secretion in the human colon

Abstract

Relationships between electrochemical forces and electrolyte transport were examined during colonic perfusion in 8 healthy volunteers. In addition, mucus was collected from the normal rectums of 25 patients. During perfusion, sodium was absorbed against electrochemical gradients and bulk water flow, consistent with active absorption. Potassium moved along electrochemical gradients, consistent with passive diffusion. The negative mucosal potential difference normally present in the colon should favor potassium excretion. Transport of anions was reciprocal: Chloride was absorbed, and bicarbonate secretion had features of an active process. The direction and degree of net water transport modified the movement of chloride, bicarbonate, and, to a lesser degree, potassium. Normal colonic mucus contained high concentrations of sodium, chloride, and potassium, most of which was dialyzable in vitro. The results imply that active sodium absorption influences water and electrolyte conservation in the human colon and that impairment of sodium transport, excessive mucus excretion, and changes of potential difference could contribute to fecal electrolyte losses in diarrhea.