VESICLE FUSION PROTEINS IN RAT INNER MEDULLARY COLLECTING DUCT AND AMPHIBIAN BLADDER

The delivery of water channels to the apical membrane in response to a ntidiuretic hormone (ADH) requires the targeting of channel-containing vesicles to specific sites in the membrane, followed by fusion and ex ocytosis. A complex array of proteins is now believed to mediate targe ting and fusion in eukaryotic cells. They include N-ethylmaleimide-sen sitive fusion protein (NSF), soluble NSF attachment proteins (SNAP), a nd cellubrevin, a vesicle-associated protein present in the nerve term inal. We asked whether these proteins are in epithelial cells of rat i nner medullary collecting duct (IMCD) and amphibian bladder. Immunoblo ts on both tissues showed the presence of NSF and alpha-SNAP. Cellubre vin was present in immunoblots of the IMCD, but not the bladder. Immun ogold electron microscopy showed NSF, alpha-SNAP, and cellubrevin in r at IMCD cells, with vesicular labeling. In the bladder, NSF was seen o n vesicles and aggrephores. We conclude that components of the vesicle -targeting and fusion systems are present in kidney and amphibian blad der and may mediate a wide variety of fusion events, including those i nitiated by ADH.