NHE2 is the major brush border NA/H exchanger isoform in the avian colon and is stimulated by mineralocorticoids

We previously reported that mammalian small intestinal and colonic brush borders contained both epithelial Na/H exchangers NHE2 and NHE3 Now we show that in the avian colon (chicken) NHE2 is the major functional isoform under basal conditions and when stimulated with mineralocorticoids. Hubbard chickens were maintained for 2 weeks on a high (1 gm per day) or low (0) NaCl diet. After sacrifice, the colons were removed and BB prepared by Mg precipitation and ²²Na uptake and D-[14C] glucose uptake determined in the BB vesicles NHE2 and NHR3 were separated by differential sensitivity to HOE694 (NHE2 defined as Na/H exchange inhibited by 50 uM HOE694). Low Na diet increased plasma aldosterone from 10 to 207 pg/ml. On the high NaCl diet both NHE2 and NHE3 contributed to Nail exchange but the majority was due to NHE2 (86%) Low NaCl diet significantly decreased colonic Na dependent glucose uptake and increased colonic BB Na/H exchange (342 vs 190 pmol/mg protein/5 min), the increase in BB Na/H exchange was entirely due to an increase in NHE2 (319 vs 163) with no change in NHE3 activity, (23 vs 27) NHE2 and NHE3 were present in colonic BB but not BEM immunocytochemistry, and Western analysis showed that low Na diet increased the amount of NHE2 in the colonic BB. Summary 1) NHE2 and NHE3 are both present in the BB and not BLM of chicken colonocytes; 2) NHE2 is the major physiologic colonic BB Na/H exchanger under basal conditions; 3) increasing aldosterone increases colonic BB Na/H exchange and decreases Na dependent glucose uptake; 4) the aldosterone stimulation of colonic brush border Na/H exchange is due to increased activity and amount of NHE2.