Ml. Vitale et al., CHROMAFFIN CELL CORTICAL ACTIN NETWORK DYNAMICS CONTROL THE SIZE OF THE RELEASE-READY VESICLE POOL AND THE INITIAL RATE OF EXOCYTOSIS, Neuron, 14(2), 1995, pp. 353-363
Morphological, biochemical, and membrane capacitance measurements were
used to study the role of cortical filamentous actin (F-actin) in exo
ctyosis. Fluorescence and electron microscopy of resting chromaffin ce
lls revealed a cortical actin network that excluded secretory vesicles
from the subplasmalemmal area. Phorbol ester (PMA) treatment disrupte
d cortical F-actin and increased both the number of vesicles within th
e 0-50 nm subplasmalemmal zone and the initial rate of stimulated cate
cholamine release. In PMA-pretreated cells, membrane capacitance studi
es showed an increased number of vesicles fusing with the plasmalemma
during the first two depolarizations of a train. PMA did not affect vo
ltage-dependent Ca2+ influx. The total number of vesicles fused with t
he plasma membrane correlated well with the number of vesicles occupyi
ng the 0-50 nm cortical zone. Therefore, cortical F-actin disassembly
allows translocation of vesicles to the plasmalemma in preparation for
exocytosis.