Cdna cloning of a functional water channel from toad urinary
bladder epithelium.
Ma, Tonghui, Baoxue Yang, and A. S. Verkman.
Departments of Medicine and Physiology, Cardiovascular Research
Institute, University of California, San Francisco, CA, 94143-0521,
U.S.A.
APStracts 3:0190C, 1996.
A cDNA was cloned from the epithelium of (Bufo marinas) toad urinary
bladder based on homology to the mammalian aquaporins. The cDNA (947
bp, AQP-t1) encoded a 272 amino acid protein with 76% identity to
mammalian water channel CHIP28 (AQP-1) and 88% identity to frog water
channel FA-CHIP. AQP-t1 cDNA was nearly identical to a fragment of a
non-functional cDNA cloned recently from toad bladder ("AQP
-TB", Siner et al., Am. J. Physiol. 270:C372-C381, 1996), except
for reading frame shifts at bp 253, 264 and 682, two single amino
acid deletions, a different 3'-coding sequence downstream from bp
786, and a different 5'-sequence upstream from bp 9. Water
permeability (Pf) in Xenopus oocytes expressing AQP-t1 cRNA was
strongly increased from (0.83 + 0.06) x 10-3 cm/s (water injected
control) to (17 + 4) x 10-3 cm/s with 80% inhibition by 0.3 mM HgCl2;
glycerol and urea permeabilities were not increased. Northern blot
analysis showed a single AQP-t1 mRNA size of 2.8 kb in eye >
lung > urinary bladder > skin > stomach heart, brain
and intestine. AQP-t1 mRNA expression was not changed by dehydration
of toads for 3 days or an 8 hour stimulation of water permeability in
isolated bladders by forskolin. These results indicate that the
epithelium of toad urinary bladder expresses a functional homolog of
AQP-1 and FA-CHIP which is probably not vasopressin regulated.
Further studies are needed to localize the AQP-t1 protein.
Received 6 May 1996; accepted in final form 31 May 1996.
APS Manuscript Number C241-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 June 96