IMMUNOLOCALIZATION OF THE MERCURIAL-INSENSITIVE WATER CHANNEL AND GLYCEROL INTRINSIC PROTEIN IN EPITHELIAL-CELL PLASMA-MEMBRANES

Two water channel homologs were cloned recently from rat kidney, mercu rial-insensitive water channel (MIWC) and glycerol intrinsic protein ( GLIP). Polyclonal antibodies were raised against synthetic C-terminal peptides and purified by affinity chromatography. MIWC and CLIP antibo dies recognized proteins in rat kidney with an apparent molecular mass of 30 and 27 kDa, respectively, and did not cross-react, By immunoflu orescence, MIWC and GLIP were expressed together on the basolateral pl asma membrane of collecting duct principal cells in kidney, By immunoh istochemistry, MIWC and GLIP were expressed on tracheal epithelial cel ls with greater expression of GLIP on the basal plasma membrane and Mn ;VC on the lateral membrane; only MIWC was expressed in bronchial epit helia, In eye, GLIP was expressed in conjunctival epithelium, whereas MIWC was found in iris, ciliary body, and neural cell layers in retina , MIWC and GLIP colocalized on the basolateral membrane of villus epit helial cells in colon and brain ependymal cells, Expression of MIWC an d GLIP was not detected in small intestine, liver, spleen, endothelia, and cells that express water channels CHIP28 or WCH-CD, These studies suggest water/solute transporting roles for MIWC and GLIP in the urin ary concentrating mechanism, cerebrospinal fluid absorption, ocular fl uid balance, fecal dehydration, and airway humidification. The unexpec ted membrane colocalization of MIWC and GLIP in several tissues sugges ts an interaction at the molecular and/or functional levels.