Abstract
Two mercurial-inhibitable water-transporting proteins have been identified: CHIP28, an erythrocyte water channel also expressed in kidney tubules and selected extrarenal epithelia, and WCH-CD, a kidney collecting duct water channel. In searching for a protein responsible for the high transcellular water permeability in lung alveolus, we cloned a 32-kDa water channel (mercurial-insensitive water channel (MIWC)) from a rat lung cDNA library with several novel features. Water permeability was strongly increased in Xenopus oocytes expressing MIWC in a mercurial-insensitive manner, in contrast to known water channels. By in situ hybridization, MIWC showed an unique distribution in cells that do not express CHIP28, including kidney papillary vasa recta, cells lining the subarachnoid space and ventricles in brain, the inner nuclear layer in retina, and the conjunctival epithelium. An alternatively spliced form of MIWC with a 165-base pair deletion in the coding sequence was also identified; relative expression of the spliced mRNA was tissue-specific. The MIWC water channel may participate in the urinary concentrating mechanism, the absorption of cerebrospinal fluid, and other physiological processes.
Highlights
From the Departments of Medicine a n d Physiology, Cardiovascular Research Institute, University of California, Sun Francisco, California 94143-0532 channel expressed exclusivelyin mammalian kidney collecting duct (WCH-CD)l was identified recently (13, 14)
A novel mercurial-insensitivewaterchannel(MIWC)reported here was cloned fromrat lung but was expressed stronginlykidney inner medulla, in cells involved in the reabsorptionof cerebrospinal fluid inbrain, and in other tissues
TWO mercurial-inhibitablewater-transporting proteins have beenidentified CHIP28, an e&throcsewa- cDNA Cloning of MIWC-Degenerate oligonucleotideprimers were ter channel expressed in kidney tubules and se- designed against conservedmotifs in MIP26familymembers (14): lectedextrarenalepithelia,and
Summary
From the Departments of Medicine a n d Physiology, Cardiovascular Research Institute, University of California, Sun Francisco, California 94143-0532 channel expressed exclusivelyin mammalian kidney collecting duct (WCH-CD)l was identified recently (13, 14). A novel mercurial-insensitivewaterchannel(MIWC)reported here was cloned fromrat lung but was expressed stronginlykidney inner medulla, in cells involved in the reabsorptionof cerebrospinal fluid inbrain, and in other tissues. TWO mercurial-inhibitablewater-transporting proteins have beenidentified CHIP28, an e&throcsewa- cDNA Cloning of MIWC-Degenerate oligonucleotideprimers were ter channel expressed in kidney tubules and se- designed against conservedmotifs in MIP26familymembers (14): lectedextrarenalepithelia,and
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