Multiple Roles of Actin Cytoskeleton in Catecholamine Release from Chromaffin Cell

In adrenal chromaffin cells, it is generally accepted that sub-plasmalemmal actin network acts as a barrier to secretory vesicles.1 On the other hand, we have demonstrated previously that myosin light chain kinase which regulates actin-myosin interaction are required for ATP-dependent priming or for step before the priming of exocytosis in adrenal chromaffin cells,2 and suggested that actin-myosin interaction is required for the vesicle recruitment in these cells. In order to clarify the implication of actin-myosin interaction and of actin cytoskeleton in the mechanism of CA release, we studied the effects of Mycalolide B (MLB), Cytochalasin D (CD), and Wortmannin (WT) on the vesicle movement and kinetics of exocytotic events. Mycalolide B depolymerizes F-actin to G-actin and therefore inhibits actin-myosin interaction.3 Cytochalasin D severs F-actin into short filaments, but does not inhibit actin-myosin interaction.3 Wortmannin inhibit the phosphorylation of myosin light chain thus inhibit actin-myosin interaction, but does not depolymeraize F-actin.4