Address for correspondence: Dr. J-M. Trifaró, Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, 451 Smyth Road, Ottawa, ON, K1H 8M5 Canada. Voice: 613-562-5448; fax: 613-562-5637
jtrifaro{at}uottawa.ca
Ann. N.Y. Acad. Sci. 971: 222-231 (2002).
Neurosecretory cells, including chromaffin cells, possess a
mesh of filamentous actin underneath the plasma membrane. It
has been proposed that filamentous actin network separates the
secretory vesicles into two compartments: the reserve pool and
the release-ready vesicle pool. Disassembly of chromaffin cell
cortical filamentous actin in response to stimulation allows
the movement of vesicles from the reserve pool into the release-ready
vesicle pool. Electron microscopy of cytoskeletons revealed
the presence of polygonal areas almost devoid of actin filaments
in stimulated cells. The percentage of stimulated cells showing
disrupted cytoskeleton correlates well with the increase in
secretion in these cells. Fine filaments also remain in these
areas of disassembly, and these reacted with actin antibodies,
as demonstrated by immunogold staining. In addition, the movement
of vesicles between pools requires Ca
2+ and ATP, a condition
for activation of a molecular motor. Confocal microscopy images
demonstrated colocalization of myosin Va with dopamine-ß-hydroxylase.
Cell depolarization induced the dissociation of myosin Va from
chromaffin vesicles. 2,3-Butadione-2-monoxime (BDM), an inhibitor
of myosin ATPase, inhibited secretion, suggesting a blockage
for chromaffin vesicle transport between the reserve pool and
the release-ready vesicle pool. On the other hand, myosin II
subcellular distribution was not affected by cell depolarization.
Confocal microscopy images show myosin II to be localized in
the cell cortex and in some perinuclear structures. Chromaffin
vesicles were not stained by myosin II antibody.
