Snap-23 in rat kidney: co-localization with aquaporin-2 in collecting duct vesicles. Inoue, Takeaki, S Ren Nielsen, Beatrice Mandon, James Terris, Bellamkonda K. Kishore and Mark A. Knepper. 1Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1603, 2 Department of Cell Biology, Institute of Anatomy, University of Aarhus, Aarhus, DK, 3Department of Physiology, Uniformed Services University of the Health Sciences, Bethesda, MD
APStracts 5:0147F, 1998.
Vesicle targeting proteins ("SNAREs") have been proposed to direct vasopressin-induced trafficking of aquaporin-2 water channels in kidney collecting ducts. A newly identified SNARE protein, SNAP -23, is proposed to mediate vesicle targeting to the plasma membrane in diverse tissues. The current studies were done to determine whether SNAP-23 is expressed in collecting ducts with an intracellular distribution compatible with a role in aquaporin-2 trafficking. RT-PCR demonstrated SNAP-23 mRNA in microdissected collecting ducts and other tubular segments including the proximal tubule and thick ascending limb. Immunoblotting using a polyclonal antibody raised against a COOH-terminal peptide revealed a solitary band at an apparent molecular weight of 30kDa in renal medullary membrane fractions and inner medullary collecting duct suspensions. Differential centrifugation revealed that SNAP-23 is present in membrane fractionss including the low-density fraction enriched in intracellular vesicles. Immunocytochemistry revealed SNAP-23 labeling at both the apex and the cytoplasm of collecting duct principal cells. Immunoblotting of intracellular vesicles immunoisolated using an aquaporin-2 antibody revealed the presence of both SNAP-23 and VAMP-2 in aquaporin-2-bearing vesicles. We conclude that SNAP-23 is strongly expressed in collecting duct principal cells, consistent with a role in vasopressin-regulated trafficking of aquaporin-2. However, localization of SNAP-23 in both intracytoplasmic vesicles and plasma membranes suggests a function different from that originally proposed for SNAP-25 in synaptic vesicle targeting. 

Received 13 May 1998; accepted in final form 20 August 1998.
APS Manuscript Number F114-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 21 September 1998