Distribution of aquaporin-4 water channel expression within rat
kidney.
Terris, James, Carolyn A. Ecelbarger, David Marples, Mark A. Knepper,
and Soren Nielsen.
Laboratory of Kidney and Electrolyte Metabolism, National Heart,
Lung and Blood Institute, National Institutes of Health, Bethesda, MD
20892, Department of Cell Biology, Institute of Anatomy, University
of Aarhus, DK-8000 Aarhus, Denmark
APStracts 2:0153F, 1995.
The aquaporins are a family of transmembrane proteins that function as
molecular water channels. Recently, a mercurial insensitive water
channel (MIWC or aquaporin-4) has been cloned and its mRNA was found
to be expressed strongly in kidney inner medulla and several nonrenal
tissues. We prepared affinity-purified polyclonal anti-peptide
antibodies to aquaporin-4 (AQP4) to define the regional distribution
and cellular location of this water channel within the kidney.
Immunoblotting of membrane fractions from different regions of the
kidney revealed strongest expression in the base of the renal inner
medulla with detectable levels also in the inner medullary tip, but
little or no expression in the outer medulla or cortex.
Immunocytochemistry (light microscopy) revealed renal AQP4 labeling
exclusively in the collecting duct principal cells, chiefly in the
proximal two-thirds of the inner medullary collecting duct. Little or
no expression was seen in the outer medullary and cortical collecting
ducts. Immunoelectron microscopy demonstrated AQP4 labeling of the
basolateral membrane of IMCD cells, with relatively little labeling
of intracellular vesicles. Differential centrifugation of inner
medullary homogenates also revealed a lack of distribution to the
vesicle-enriched fraction which contains the vasopressin-regulated
water channel, aquaporin-2. In contrast to aquaporin-2 and aquaporin
-3, water restriction of rats did not increase the level of AQP4
expression. These results suggest a possible role for AQP4 in the
basolateral exit of water from the inner medullary collecting duct.
Received 26 April 1995; accepted in final form 20 June 1995.
APS Manuscript Number F137-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.