In searching for a basolateral membrane water trans-porter in rat kidney with homology to channel formingintegral protein (CHIP28), water channel-collecting duct (WCH-CD), and mercurial-insensitive water chan-nel (MIWC), we cloned a new member of the major in-trinsic protein family (GLIP, -cero1 Intrinsic B o -tein). GLIP cDNA had an 865-base pair open reading frame encoding a 30.6-kDa protein with 19-23% amino acid identity to the water channels and 36% identity to the bacterial glycerol facilitator GlpF. Northern blot analysis showed a 6.6-kilobase mFWA encoding GLIP in kidney, brain, and lung; RT-PCWSouthern blot analysis indicated expression of GLIP in kidney, brain, lung, eye, colon, stomach, and skeletal muscle, but not in heart, liver, and spleen. In situ hybridization in rat kidney showed GLIP mRNA expression in medullary collecting duct. Immunofluorescence with a peptide-derived poly-clonal antibody showed GLIP protein expression in ba-solateral membrane of kidney collecting duct principal cells and brain meningeal cells. Functional measure-ments in Xenopus oocytes expressing GLIP cRNA showed a>2O-fold increase in [SHlglycerol uptake com-pared with water-iqjected oocytes; glycerol uptake was inhibited 88% by diisothiocyanodisdfonic stilbene (0.2mm) and 36% by phloretin (0.25mm). GLIP did not func-tion as a transporter for water, urea, inositol, glucose, lactate, and monovalent ions. Glycerol uptake in oocytes expressing CHIP28 and MIWC was not different from that in water-injected controls. GLIP represents the first mammalian water channel homolog that selectively transports a solute other than water. The physiological substrate(s) and role(s) of GLIP remain to be elucidated.