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.