Expression of multiple Na+/H+ exchanger isoforms in cultured epithelial cells from rat efferent duct and cauda epididymidis

Although earlier work has pointed to the presence of Na+/ H+ exchangers (NH Es) in the rat epididymis, little is known about the regional distribution of various NHE isoforms and their functions. In the present work, expressio n of different isoforms of NHE in cultured epithelia of the efferent duct a nd cauda epdidymidis were studied. Reverse transcription-polymerase chain r eaction revealed the presence of NHE1, NHE2, and NHE3, but not NHE4, messag e in both cultured epithelia. Western blot analysis detected the presence o f NHE1 and NHE2 proteins in both cultured epithelia, but NHE3 protein was o nly detected in the cultured epithelial cells from the efferent duct. Immun ohistochemical studies demonstrated that NHE2 was localized in the cytoplas m of the ciliated cells, whereas NHE3 was localized at the apical membrane of the principal cells of the efferent duct. The NHE activities in both cul tured epithelia were inhibited by 10 muM HOE-694 (3-methylsulphonyl-4-piper idinobenzoyl guanidine methanesulphonate), a NHE1 inhibitor, by approximate ly 76%. The HOE-694-resistant NHE activities in the cultured epithelia of e fferent duct and cauda epididymidis were completely inhibited by 20 muM S32 26 (3-[2-(3-guanidino-2-methyl-3-oxo-propenyl)-5-methyl-phenyl]-N-isopropyl idene-2-methyl-acrylamide dihydrochloride), a NHE3 inhibitor, and 300 muM H OE-694 (a dose that can completely block NHE2), respectively. These results indicated that NHE1, NHE2, and NHE3 were expressed in the cultured epithel ial cells of the efferent duct, whereas only NHE1 and NHE2 were expressed i n the cultured epithelial cells of the cauda epididymidis. It is suggested that NHE1 may provide "housekeeping" functions in both epithelia, whereas N HE2 in the cauda epididymidis and NHE3 in the efferent duct may be involved in Na+ reabsorption and regulation of pH of the luminal fluid.