Seminars Archive

DYNAMICS OF REGULATED EXOCYTOSIS AND VESICLE TRAFFICKING N ASTROCYTES

Abstract
We study the secretory activity of astrocytes by electrophysiological and optical methods. By the patch-clamp technique we found that astrocytes exhibit Ca2+-dependent increases in membrane capacitance (Cm), reflecting surface area changes. Although similar to neurons, the process is at least one order of magnitude slower. The increase in Cm may be rate limited by the delivery and fusion of a number of vesicle types. By confocal microscopy we monitored the release of florescently tagged peptides, such as atrial natriuretic peptide (ANP). We observed non-directional and also directional mobility, suggesting a role for cytoskeleton in vesicle traffic. Pre-fusion vesicle transport (transport leading to exocytosis) of peptidergic vesicles was studied by fluorescently labeled ANP, and post-fusion (post-exocytosis) transport of glutamatergic and peptidergic vesicles by labeling vesicles with antibodies against specific membrane or lumenal vesicle proteins. Both pre-fusion and post-fusion traffic strongly depended on intact cytoskeleton. Prefusion traffic was insensitive to increases in [Ca2+]i, however the post-fusion vesicle mobility was sensitive to changes in [Ca2+]i. Peptidergic vesicles and lysotracker-positive vesicles exhibited stimulation-dependent mobility inhibition, whereas the anti-VGLUT1 antibody-positive vesicles exhibited an increased mobility upon an increase in [Ca2+]i. Thus, distinct vesicle types respond differently to stimulation. Under pathological conditions vesicle traffic may be disregulated in astrocytes.