Expression of AE2 anion exchanger in mouse intestine

We have characterized expression of anion exchanger 2 (AE2) mRNA and protei n in the mouse intestine. AE2 mRNA abundance was higher in colon than in mo re proximal segments. AF2a mRNA was more abundant than AE2b mRNA throughout the intestine, and AE2c mRNA was expressed at very low levels. This AE2 mR NA pattern contrasted with that in mouse stomach, in which AE2c > AE2b > AE 2a. AE2 polypeptide abundance as detected by immunoblot qualitatively paral leled that of mRNA, whereas AE2 immunostaining exhibited a more continuous decrease in intensity from colon to duodenum. AE2 polypeptide was more abun dant in colonic surface cells than in crypts, whereas ileal crypts and vill i exhibited similar AE2 abundance. AE2 was also observed in mural and vascu lar smooth muscle. Localization of AE2 epitopes was restricted to the basol ateral membranes of epithelial cells throughout the intestine with three ex ceptions. Under mild fixation conditions, anti-AE2 amino acids (aa) 109-122 detected nonpolarized immunostaining of ileal enterocytes and of Paneth ce ll granule membranes. An epitope detected by anti-AE2 aa 1224-1237 was also localized to subapical regions of Brunner's gland ducts of duodenum and up per jejunum. These localization studies will aid in the interpretation of a nion exchanger function measured in epithelial sheets, isolated cells, and membrane vesicles.