Redistribution of aquaporin-2 water channels induced by vasopressin
in rat kidney inner medullary collecting duct.
Marples, David, Mark A. Knepper, Erik Ils Christensen, & Sren
Nielsen.
Department of Cell Biology, Institute of Anatomy, University of
Aarhus, DK-8000 Aarhus C, Denmark, Laboratory of Kidney and
Electrolyte Metabolism, National Heart, Lung and Blood Institute,
Building 10, Room 6N307, National Institutes of Health, Bethesda,
Maryland
APStracts 2:0155C, 1995.
Aquaporin-2 (AQP2) is the predominant vasopressin regulated water
channel of the renal collecting duct. We tested whether vasopressin
induces translocation of AQP2 from intracellular vesicles into the
apical plasma membrane. AQP2 was quantitated in plasma membrane and
intracellular vesicle fractions prepared from the inner medulla of
one kidney from each rat before or 20 min after i.v. dDAVP treatment,
using immunoblotting and densitometry. Contralateral kidneys were
prepared for immunofluorescence and immuno-electron microscopy.
Immunoblotting revealed that, compared with untreated controls, dDAVP
treatment significantly increased the fraction of AQP2 protein
associated with the plasma membrane fraction relative to
intracellular vesicles. This increase averaged 2.0 fold in untreated
rats, and 2.9 fold in rats water loaded for 12 hours. Water loading,
presumably by suppressing circulating vasopressin levels, decreased
the fraction of AQP2 associated with the plasma membrane by 55%,
suggesting retrieval of AQP2 from the plasma membrane. In rats
sequentially thirsted for 48 hours to increase expression, and then
water loaded for 72 hours to minimize plasma membrane labeling, dDAVP
caused a 12 fold increase in the plasma membrane to intracellular
vesicle labeling ratio. The accentuation of the dDAVP response seen
after water loading is consistent with the observed increase in the
fraction of AQP2 in the intracellular pool available for insertion.
Immunofluorescence confirmed a marked dDAVP-induced redistribution of
AQP2 from intracellular to plasma membrane domains. Furthermore,
quantitative immuno-electron microscopy demonstrated a 3.4 fold
increase in apical plasma membrane to intracellular vesicle labeling
ratio. These results provide a direct, in vivo, demonstration of
vasopressin-induced translocation of AQP2 into the apical plasma
membrane.
Received 12 December 1994; accepted in final form 16 March 1995.
APS Manuscript Number C714-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 April 1995.