Aquaporin-3 water channel localization and regulation in rat kidney. Ecelbarger, Carolyn A., James Terris, Gustavo Frindt, Miriam Echevarria, David Marples, Soren Nielsen, and Mark A. Knepper. Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, Department of Physiology and Biophysics, Cornell University Medical College, 1300 York Avenue, New York, NY 10021, Department of Cell Biology, Institute of Anatomy, University of Aarhus, DK-8000 Aarhus, Denmark
APStracts 2:0090F, 1995.
The aquaporins are a family of water channels expressed in several water-transporting tissues including the kidney. We have used a peptide-derived affinity-purified polyclonal antibody to aquaporin-3 (AQP-3), to investigate its localization and regulation in the kidney. Immunoblotting experiments showed expression in both renal cortex and medulla with greatest expression in the base of the inner medulla. Subcellular fractionation of membranes using progressively higher centrifugation speeds revealed that AQP-3 is present predominantly in the 4,000 Xg and 17,000 Xg pellets and, in contrast to AQP-2, is virtually absent from the high-speed (200,000 Xg) pellet that contains small intracellular vesicles. Immunocytochemistry and immunofluorescence studies revealed that labeling is restricted to the cortical, outer medullary and inner medullary collecting ducts. Within the collecting duct, principal cells were labeled, whereas intercalated cells were unlabeled. Consistent with previous immunofluorescence studies [11,15], the labeling was confined to the basolateral domain. Immuno-electron microscopy, using the immunogold technique in ultrathin cryosections, demonstrated a predominant labeling of the basolateral plasma membranes. In contrast to previous findings with AQP-2, there was only limited AQP-3 labeling of intracellular vesicles, suggesting that this water channel is not regulated acutely through vesicular trafficking. Immunoblotting studies revealed that thirsting of rats for 48 hours approximately doubled the amount of AQP-3 protein in the inner medulla. These studies are consistent with a role for AQP-3 in osmotically-driven water absorption across the collecting duct epithelium and suggest that the expression of AQP-3 is regulated on a long-term basis. 

Received 20 March 1995; accepted in final form 19 May 1995.
APS Manuscript Number F95-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 May 1995.