Extrarenal tissue distribution of CHIP28 water channels by in situ hybridization and antibody staining

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Abstract
This study is an extension of in situ hybridization experiments showing expression of mRNA encoding CHIP28 in selected epithelial or endothelia in spleen, colon, lung, and eye (H. Hasegawa, R. Zhang, A. Dohrman, and A. S. Verkman. Am. J. Physiol. 264 (Cell Physiol. 33): C237-C245, 1993). Additional tissues from rat were screened by in situ hybridization, and tissues from rat and humans were stained with a polyclonal anti-CHIP28 antibody. Northern blot showed the 2.8-kilobase mRNA encoding CHIP28 in kidney, lung, and heart. In situ hybridization showed strong hybridization in epithelial cells in choroid plexus, iris, ciliary body, and lens and in epithelial and subepithelial layers of trachea. Except for colonic crypts, specific hybridization was not observed in the gastrointestinal tract, liver, thyroid gland, and muscle. Immunoblot of tissues from exsanguinated rats showed immunoreactive CHIP28 protein in kidney, lung, trachea, and heart. In fixed frozen rat and/or human tissues, the anti-CHIP28 antibody stained epithelial cells in kidney proximal tubule and thin limb of Henle, lung alveolus, bronchial mucosa and glands, choroid plexus, ciliary body, iris, lens surface, colonic crypt, sweat gland, pancreatic acini, gallbladder epithelium, and placental syncytial trophoblast cells. Endothelial cells were stained in many tissues. These studies indicate a wide and selective CHIP28 tissue distribution, suggesting an important role for CHIP28 in fluid transport. The absence of CHIP28 in many nonrenal membranes believed to be water permeable suggests the existence of non-CHIP28 water transporters.