XXXX kidney papilla contains abundant synaptobrevin protein that participates in the fusion of antidiuretic hormone-regulated water channel-containing endosomes in vitro.

@entity59350 @entity14354 @entity35 @entity116 @entity6085 @entity413 @entity855
@entity6085 ( @entity6085 ) regulates renal water excretion by altering the permeability of the collecting duct to water. @entity6085 -responsive epithelial cells are the major cell type lining kidney tubules in the inner medulla and papilla. @entity6085 modulates apical membrane water permeability by the insertion and removal of vesicles containing aquaporin collecting duct water channel protein (now termed @entity14354 ). To identify and characterize proteins responsible for trafficking of @entity14354 -containing vesicles, we utilized antibody and cDNA probes to synaptobrevin b (also termed @entity59350 , for @entity59350 ), a protein that mediates synaptic vesicle exocytosis in the brain and whose structural homologs are now considered to be components of a complex responsible for intracellular vesicle fusion in all cells. We now report that @entity35 kidney inner medulla and papilla contain abundant synaptobrevin protein. Only light endosomes, one of two types of purified papillary @entity14354 -containing endosomes, possess synaptobrevin. Light endosomes fuse in vitro by means of an @entity855 -dependent process that is significantly inhibited when endosomes are preincubated with either anti-synaptobrevin antibody or @entity116 toxin. These data define a functional role for a synaptobrevin protein in the fusion of endosomes in vitro. The presence of abundant synaptobrevin proteins in endosomes containing @entity14354 water channels, as well as insulin-sensitive @entity413 transporters [Cain, C. C., Trimble, W. S. _ Lienhard, G. E. (1992) J. Biol. Chem. 267, 11681-11684], and in cells of Malpighian tubules responsible for urine formation in insects [Chin, A. S., Burgess, R. W., Wong, B. R., Schwartz, T. L. _ Scheller, R. H. (1993) Gene 131, 175-181] suggests a specialized role for synaptobrevin in vesicle-mediated membrane transport modulated by peptide hormones.
