Background: The absorption of water and ions (especially Na+ and Cl−) is an important function of colonic epithelial cells in both physiological and pathophysiological conditions. Despite the comprehensive animal studies, there are only scarce available data on the ion transporter activities of the normal and inflamed human colon. Methods: In this study, 128 healthy controls and 69 patients suffering from ulcerative colitis (UC) were involved. We investigated the expressional and functional characteristics of the Na+/H+ exchangers (NHE) 1–3, the epithelial sodium channel (ENaC), and the SLC26A3 Cl−/HCO 3− exchanger downregulated in adenoma (DRA) in primary colonic crypts isolated from human biopsy and surgical samples using microfluorometry, patch clamp, and real‐time reverse‐transcription polymerase chain reaction (RT‐PCR) techniques. Results: Data collected from colonic crypts showed that the activities of electroneutral (via NHE3) and the electrogenic Na+ absorption (via ENaC) are in inverse ratio to each other in the proximal and distal colon. We found no significant differences in the activity of NHE2 in different segments of the colon. Surface cell Cl−/HCO 3− exchange is more active in the distal part of the colon. Importantly, both sodium and chloride absorptions are damaged in UC, whereas NHE1, which has been shown to promote immune response, is upregulated by 6‐fold. Conclusions: These results open up new therapeutic targets in UC. (Inflamm Bowel Dis 2011;)

In the colonic mucosa of patients with active UC, NHE3 transport capacity was found significantly decreased despite correct NHE3 location and abundance in the brush border, independent of current treatment. These findings suggest functional NHE3 transport as a novel factor for inflammatory diarrhea in UC patients.

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