AGI Apr. 39/4

Koyama, Kaori, Iwao Sasaki, Hiroo Naito, Yuji Funayama, Kouhei Fukushima, Michiaki Unno, Seiki Matsuno, Hisayoshi Hayashi, and Yuichi Suzuki. Induction of epithelial Na1 channel in rat ileum after proctocolectomy. Am. J. Physiol. 276 (Gastrointest. Liver Physiol. 39): G975– G984, 1999.—In patients with colectomy, epithelial transport function in the remnant small intestine can be regulated in response to the increased fecal electrolyte and fluid loss. Using a rat colectomy model, we investigated the Na1 and K1 transport mechanisms underlying the intestinal response. Proctocolectomy with ileoanal anastomosis was performed on rats. The small intestinal mucosa was mounted in Ussing chambers; then short-circuit currents and 22Na1 fluxes were measured. mRNA expression of the epithelial Na1 channel (ENaC) was determined by Northern blotting. Amiloridesensitive, electrogenic Na1 absorption appeared in the ileum after proctocolectomy. This functional change was accompanied by the chronological induction of mRNAs for a-, b-, and g-subunits of the ENaC in the ileum. Tetraethylammoniumsensitive short-circuit current was also activated. We conclude that electrogenic Na1 absorption and probably K1 secretion are induced in the ileum after proctocolectomy. This induction of electrogenic Na1 absorption is probably mediated by the increase in the mRNA levels for all three types of subunits of the ENaC and may contribute to the recovery from the increased fecal Na1 loss.