Electrical potential difference and sodium and potassium fluxes across rectal mucosa in ulcerative colitis.

The transmucosal electrical potential difference (pd) and the sodium and potassium flux rates (using a dialysis method) have been measured in the rectum and distal sigmoid colon of patients with ulcerative colitis and compared with measurements made in individuals having normal bowel function. In active colitis, a very low transmucosal pd was found and was associated with loss of the characteristic ability of the mucosa to absorb sodium against considerable electrochemical gradients; a marked increase in the plasma-to-lumen sodium flux rate, suggesting increased leakiness of the mucosa; and loss of the active sodium absorption mechanism. In resolving colitis, the pd was higher and all these changes of sodium transport tended to return towards normal. With full recovery, epithelial function was normal to the present tests. Potassium secretion rate showed little difference at various stages of the disease, but the nearly normal secretion of potassium in ulcerative colitis when the pd was low suggested that potassium loss to the lumen was excessive. Mucus collected from patients with ulcerative colitis had a relatively high sodium and potassium content. Measurement of pd and absorption by using a dialysis tube offers a simple means of rapid assessment of mucosal functional integrity.