Selective decreases in levels of mRNA encoding a water channel (AQP3) in ileal mucosa after ileostomy in the rat

Water channels (aquaporins) provide pathways for water permeation in a vari ety of epithelial. Aquaporin-3 (AQP3) has been localized to the basolateral membranes of epithelial cells in the small intestine, but mechanisms that regulate its expression and function have not been explored. To determine w hether luminal content may influence intestinal AQP3 gene expression, adult Sprague-Dawley rats underwent sham laparotomy (N = 11) or loop ileostomy ( N = 9) and were killed 8 days after procedures. Northern blot analysis was used to measure messenger RNA (mRNA) levels for AQP3 and the Na+/K+ ATPase, a housekeeping transporter that regulates cellular levels of Na+ and K+. A t sacrifice, histologic examination revealed only minimal changes in mucosa l morphology. In sham animals, Na/K mRNA levels increased moderately in dis tal regions of the small intestine. Ileostomy did not alter these levels in any region. Tn contrast, in sham animals, AQP3 mRNA levels increased along the length of the intestine and were markedly higher in the distal ileum. Diversion of luminal contents decreased AQP3 mRNA levels in the postileosto my region by 30% to 50%. These findings indicate regional variations in exp ression of the AQP3 water channel in mucosa of the small intestine. In addi tion, they suggest that AQP3 gene expression may depend on the presence of luminal contents.