IN BIRDS, NHE2 IS MAJOR BRUSH-BORDER NA+ H+ EXCHANGER IN COLON AND ISINCREASED BY A LOW-NACL DIET/

We previously reported that mammalian small intestinal and colonic bru sh borders (BBs) contained both epithelial Na+/H+ exchangers NHE2 and NHE3. We now show that, in the avian (chicken) colon, NHE2 is the majo r functional isoform under basal conditions and when stimulated by a l ow-NaCl diet. Hubbard chickens were maintained for 2 wk on a high- or low-NaCl diet. After the chickens were killed, the ileum and colon wer e removed, and BBs were prepared by Mg2+ precipitation and Na-22 and D -[C-14]glucose uptake determined in the BB vesicles. NHE2 and NHE3 wer e separated by differential sensitivity to HOE-694 (NHE2 defined as Na +/H+ exchange inhibited by 50 mu M HOE-694). Chickens on a low-Na+ die t have increased plasma aldosterone (10 vs. 207 pg/ml). On the high-Na Cl diet, both NHE2 and NHE3 contributed to ileal and colonic apical Na +/H+ exchange, contributing equally in ileum, but NHE2 being the major component in colon (86%). Low-NaCl diet significantly increased ileal and colonic BB Na+/H+ exchange; the increase in BB Na+/H+ exchange in both ileum and colon was entirely due to an increase in NHE2 with no change in NHE3 activity. In contrast, low-NaCl diet decreased ileal an d colonic Na+-dependent D-glucose uptake. Western analysis showed that low-Na+ diet increased the amount of NHE2 in the ileal and colonic BB and decreased the amount of ileal Na+-dependent glucose transporter S GLT1. Both NHE2 and NHE3 were present in the apical but not basolatera l membranes (BLM) of ileal and colonic epithelial cells. In summary, 1 ) NHE2 and NHE3 are both present in the BB and not BLM of chicken ileu m and colon; 2) NHE2 is the major physiological colonic BB Na+/H+ exch anger under basal conditions; 3) low-NaCl diet, which increases plasma aldosterone, increases ileal and colonic BB Na+/H+ exchange and decre ases Na+-dependent D-glucose uptake; 4) the stimulation of colonic BB Na+/H+ exchange is due to increased activity and amount of NHE2; and 5 ) the inhibition of ileal D-glucose uptake is associated with a decrea se in SGLT1 amount. NHE2 is the major chicken colonic BB Na+/H+ exchan ger.