Differential expression of ileal Na+/H+ exchanger isoforms after enterectomy

Background, Na+/H+ exchangers (NHE) are transporters involved in the absorp tion of NaCl along the gastrointestinal tract. The aim of this study was to determine the expression pattern of the intestinal brush border NHE isofor ms 2 and 3 following massive small bowel resection (SBR). Additionally, the effect of epidermal growth factor (EGF) and salivarectomy (removal of the primary source of EGF) on the expression pattern was studied. Materials and methods. ICR mice underwent a proximal SBR or sham surgery an d then received either orogastric saline or EGF (50 mu g/kg/day). In separa te experiments mice underwent salivarectomy followed by SBR or sham. Postop eratively the remaining ileum was isolated and levels of NHE-2 and NHE-3 mR NA and protein were resolved. Results. Following SBR, the expression of both mRNA and protein for NHE-3 i ncreased by similar to 2.5-fold. Treatment with EGF enhanced NHE-3 mRNA in sham animals with further elevation following SBR. The expression of NHE-2 mRNA demonstrated minimal change while protein. marginally increased (40%) following SER, EGF did not affect the expression of NHE-2 mRNA. Salivarecto my did not influence NHE-2 protein expression and inhibited the increased N HE-3 protein expression following SBR. Conclusions. Following SBR, the expression pattern for brush border NHE iso forms is distinctive. Increased expression of NHE-3 secondary to SBR and/or EGF treatment with loss of this increase following salivarectomy implies a common mechanism to-enhance enterocyte proliferation and luminal absorptio n of NaCl and water. These results suggest that NHE-3 is an important ileal exchanger following SBR. (C) 1999 Academic Press.