title: Actin is not an essential component in the mechanism of calcium-triggered vesicle fusion.
abstract: Actin has been suggested as an essential component in the membrane fusion stage of exocytosis. In some model systems disruption of the actin filament network associated with exocytotic membranes results in a decrease in secretion. Here we analyze the fast Ca2+-triggered membrane fusion steps of regulated exocytosis using a stage-specific preparation of native secretory vesicles (SV) to directly test whether actin plays an essential role in this mechanism. Although present on secretory vesicles, selective pharmacological inhibition of actin did not affect the Ca2+-sensitivity, extent, or kinetics of membrane fusion, nor did the addition of exogenous actin or an anti-actin antibody. There was also no discernable affect on inter-vesicle contact (docking). Overall, the results do not support a direct role for actin in the fast, Ca2+-triggered steps of regulated membrane fusion. It would appear that actin acts elsewhere within the exocytotic cycle.
authors.affiliation: Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, Calgary, Alta., Canada T2N 4N1.
authors.forename: Julie E
authors.initials: JE
authors.lastname: Hibbert
authors.forename: R Hussain
authors.initials: RH
authors.lastname: Butt
authors.forename: Jens R
authors.initials: JR
authors.lastname: Coorssen
mesh_terms: D051339:Actin Depolymerizing Factors / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D047630:Depsipeptides / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D008561:Membrane Fusion / Q000502:physiology*; D022142:Secretory Vesicles / Q000378:metabolism*; D047270:Strongylocentrotus purpuratus; D013844:Thiazoles / Q000378:metabolism; D053778:Thiazolidines
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D000970:Antineoplastic Agents; D019086:Bridged Bicyclo Compounds, Heterocyclic; D047630:Depsipeptides; D013844:Thiazoles; D053778:Thiazolidines; C057531:jasplakinolide; C037068:latrunculin B; D002118:Calcium