Chromaffin cell cortical actin network dynamics control the size of the release-ready vesicle pool and the initial rate of exocytosis.
Morphological, biochemical, and membrane capacitance measurements were used to study the role of cortical filamentous actin (F-actin) in exocytosis. Fluorescence and electron microscopy of resting chromaffin cells revealed a cortical actin network that excluded secretory vesicles from the subplasmalemmal area. Phorbol ester (PMA) treatment disrupted cortical F-actin and increased both the number of vesicles within the 0-50 nm subplasmalemmal zone and the initial rate of stimulated catecholamine release. In PMA-pretreated cells, membrane capacitance studies showed an increased number of vesicles fusing with the plasmalemma during the first two depolarizations of a train. PMA did not affect voltage-dependent Ca2+ influx. The total number of vesicles fused with the plasma membrane correlated well with the number of vesicles occupying the 0-50 nm cortical zone. Therefore, cortical F-actin disassembly allows translocation of vesicles to the plasmalemma in preparation for exocytosis.
Department of Pharmacology, Faculty of Medicine, University of Ottawa, Ontario, Canada.
M L
ML
Vitale
E P
EP
Seward
J M
JM
Trifaró
D000199:Actins / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D000302:Adrenal Cortex / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D002478:Cells, Cultured; D002837:Chromaffin Granules / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D004594:Electrophysiology / Q000379:methods; D004837:Epinephrine / Q000378:metabolism; D005089:Exocytosis; D007700:Kinetics; D008564:Membrane Potentials; D008854:Microscopy, Electron; D009538:Nicotine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014741:Video Recording
D000199:Actins; D009538:Nicotine; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D009638:Norepinephrine; D004837:Epinephrine