Induction of electrogenic, amiloride-sens1ti ve NA⁺ absorption in the lower small intestine after total colectomy in rats

The mechanisms underlying an adaptive increase in Na+ absorption in the small intestine were investigated after performing a total colectomy with ileo-anal anastomosis in rats. Amiloride-sensitive epithelial Na channel (ENaC) a -, β- and y-mRNAs were barely detectable in the small intestine from untreated rats, but were each abundant in the lower small intestine from the colectomized rats. The levels of a-, β-and y-subunit ENaC mRNAs increased particularly between 2wk and 4wk after colectomy. Ussing chamber experiments revealed that the amiloride-sensitive components of short-circuit current (Isc) and 22Na absorption were detected in the lower, but not in the middle, small intestine from colectomized rats. The area exhibiting amiloride-sensitive Isc within the lower small intestine was increased at 4wk than at 2wk after colectomy, while the plasma aldosterone level was markedly elevated after colectomy. It is concluded that electrogenic, amiloride-sensitive Na+ absorptive activity was induced after total colectomy as a result of parallel increases in ENaC a-, β- and y-subunit expression, which was probably mediated by the increased plasma aldosterone level. This may play an important role in recovery from fecal Na⁺ loss.