Presence of dynamin-syntaxin complexes associated with secretory granules in adrenal chromaffin cells

Dynamin proteins have been implicated in many aspects of endocytosis, inclu ding clathrin-mediated endocytosis, internalization of caveolae, synaptic v esicle recycling, and, more recently, vesicular trafficking to and from the Golgi complex. To provide further insight into the function(s) of dynamin in neuroendocrine cells, we have examined its intracellular distribution in cultured chromaffin cells by subcellular fractionation, immunoreplica anal ysis, and confocal immunofluorescence. We found that dynamin, presumably th e dynamin-2 isoform, is associated specifically with the membrane of purifi ed secretory chromaffin granules. Oligomerization state analysis by sucrose density velocity gradients indicated that the granule-associated dynamin i s in a monomeric form. Immunoprecipitation experiments coupled to double-la beling immunofluorescence cytochemistry revealed that the granular dynamin is associated with a syntaxin component that is not involved in the granule -bound SNARE complex. The possibility that dynamin participates in the coup ling of the exocytotic and endocytotic reaction through the building of a g ranular membrane subset of proteins is discussed.