KINETICS OF EXOCYTOSIS IN ADRENAL CHROMAFFIN CELLS

Upon repetitive or maintained stimulation, chromaffin cells secrete ca techolamines initially at a very high rate which then relaxes with mul tiple Kinetic components. The complex kinetics are often modeled as re sulting from the successive depletion of several functional pools of s ecretory granules which may reflect specific protein-mediated steps in granule maturation. The fastest component represents granules fully p rimed for exocytosis. This 'readily releasable pool' may, under some c ircumstances, consist of only about a dozen granules which can be rele ased within tens of milliseconds. Modulating the size of this pool may be an important way for cells to regulate secretion.