Immunolocalization and effect of dehydration on aqp3, a basolateral
water channel of kidney collecting ducts.
Ishibashi, Kenichi, Sei Sasaki, Kiyohide Fushimi, Tadashi Yamamoto,
Michio Kuwahara, and Fumiaki Marumo.
Second Department of Internal Medicine, Tokyo Medical and Dental
University, Tokyo 113, Department of Pathology, Institute of
Nephrology, Niigata University, Niigata 951; Renal Unit, Oume General
Hospital, Tokyo 198, Japan
APStracts 3:0199F, 1996.
Aquaporin 3 (AQP3) is unique in its structure: lowest homology with
other aquaporins, and in its function: significantly conductive to
both small nonelectrolytes and water. However, there is a controversy
among researchers on its water transport and induction by
dehydration. We examined its localization and the effect of
dehydration on its expression in the kidney, and its water channel
activity when expressed in Xenopus oocytes. In vitro translation
using reticulocyte lysate revealed that the size of rat AQP3 was 26
kD, and the band shifted to around 31 kD with microsomal fraction,
which was sensitive to the digestion with N-glycosidase F. In Western
blot analysis of rat kidney medulla, AQP3 appeared as a sharp band at
27 kD and a broad band at 34-40 kD. In immunohistochemistry, AQP3 was
localized to principal cells and absent in intercalated cells in
outer medulla. In inner medulla, AQP3 was restricted to inner
medullary collecting duct (IMCD) cells. AQP3 was confined to the
basolateral membrane of these cells. Although dehydration of rats for
2 days did not change the distribution pattern of AQP3 in IMCD cells,
the dehydration increased AQP3 mRNA by two folds with slight increase
of its protein level in kidney medulla. Finally, we confirmed its
water channel activity when expressed in Xenopus oocytes. The human
AQP3 stimulated osmotic water permeability (Pf) by 8 folds which was
inhibited by 0.3 mM mercury chloride by 34 % and reversed by [beta]
-mercaptoethanol. Our results indicate that AQP3 is a glycosylated
protein and a mercury sensitive water channel localized at the
basolateral membrane of principal cells and IMCD cells, and its
expression is induced by dehydration at both protein and mRNA level.
Received 13 July 1995; accepted in final form 22 October 1996.
APS Manuscript Number F230-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 November 1996