LOCALIZATION OF N-ETHYLMALEIMIDE-SENSITIVE FUSION PROTEIN IN PINEALOCYTES

N-ETHYLMALEIMIDE-sensitive fusion protein (NSF), a protein necessary f or vesicular docking and/or fusion, was detected immunohistochemically in pinealocytes. NSF was distributed similarly to synaptophysin and v acuolar-type H+-ATPase (V-ATPase), marker proteins for synaptic-like m icrovesicles (MVs) abundantly present in pinealocytes, A subcellular f ractionation study indicated that >95% of NSF was present as a membran e-bound form and that some NSF was associated with MVs. Like neuronal NSF, the protein was not solubilized from membranes with either 2 mM M g-ATP or 2% sodium carbonate, suggesting that NSF was tightly bound to the membranes. NSF was also detected in purified MVs from bovine post erior pituitaries. Since MVs are the organelles in which transmitters are stored, these results suggest that NSF is involved in the MV-media ted exocytosis of transmitters from endocrine cells.