LOCALIZATION OF MIWC AND GLIP WATER CHANNEL HOMOLOGS IN NEUROMUSCULAR, EPITHELIAL AND GLANDULAR TISSUES

It was shown recently that water channel homologs MIWC (mercurial inse nsitive water channel) and GLIP (glycerol intrinsic protein) colocaliz ed in basolateral membranes of kidney collecting duct, tracheal and co lonic epithelia, and in brain pia mater, We report here an extensive i mmunolocalization study of MIWC and GLIP in non-epithelial and glandul ar epithelial tissues in rat, Immunogold electron microscopy confirmed colocalization of MIWC and GLIP in basolateral membrane of principal cells in kidney collecting duct, However, in other epithelia, MIWC but not GLIP was expressed in basolateral membrane of parietal cells in s tomach, and in excretory tubules of salivary and lacrimal glands; GLIP but not MIWC was expressed in transitional epithelium of urinary blad der and skin epidermis, Zn the central nervous system, Mn;VC was stron gly expressed in the ependymal layer lining the aqueductal system, and in astrocytes throughout the spinal cord and in selected regions of b rain, MIWC was also expressed in a plasma membrane pattern in skeletal , but not smooth or cardiac muscle, Neither protein was expressed in s mall intestine, testis, liver, spleen and nerve, The tissue-specific e xpression of MIWC suggests a role in fluid transport and/or cell volum e regulation in stomach and glandular epithelia, The functional role o f MIWC expression in the neuromuscular system and of GLIP expression i n skin and urinary bladder is uncertain, The specific cellular sites o f MIWC expression (astrocytes, trachea, sarcolemma, gastric parietal c ells and kidney principal cells) correspond exactly to sites where ort hogonal arrays of particles (OAPs) have been visualized by freeze-frac ture electron microscopy, suggesting that MIWC may be the OAF protein.