Address for correspondence: Dr. Ronald W. Holz, Department of Pharmacology, University of Michigan Medical School, 2301 MSRB III, Ann Arbor, MI 48109-0632. Voice: 734-764-2267; fax: 734-763-4450.
holz{at}umich.edu
Ann. N.Y. Acad. Sci. 971: 232-243 (2002).
A slow ATP-dependent priming step precedes a rapid, Ca
2+-dependent
triggering step in exocytosis in chromaffin cells and in most,
if not all, differentiated secretory cells. A major component
of ATP-dependent secretion in permeabilized cells reflects the
maintenance of the polyphosphoinositides, especially PtdIns-4,5-P2.
Here we summarize recent experiments with PH-GFP (binds to PtdIns-4,5-P2)
that indicate that PtdIns-4,5-P2 is localized primarily on the
plasma membrane in chromaffin cells, and that it is this pool
that plays a role in exocytosis. It is demonstrated that transiently
expressed PH-GFP inhibits secretion in subsequently permeabilized
cells. Recent studies using total internal reflection fluorescent
microscopy (TIRFM) to measure chromaffin granule motion adjacent
to the plasma membrane are also summarized. The quantitative
analysis indicates that chromaffin granule motion is highly
restricted and suggests that chromaffin granules are caged or
tethered immediately adjacent to the plasma membrane.
