Mechanisms underlying phasic and sustained secretion in chromaffin cells from mouse adrenal slices

Neuron. 1999 Jul;23(3):607-15. doi: 10.1016/s0896-6273(00)80812-0.


Many neurosecretory preparations display two components of depolarization-induced exocytosis: a phasic component synchronized with Ca2+ channel opening, followed by a slower sustained component. We evaluated possible mechanisms underlying this biphasic behavior by stimulating mouse chromaffin cells in situ with both depolarizations and flash photolysis of caged Ca2+. From a direct comparison of the secretory responses to both stimuli, we conclude that phasic and sustained release components originate from a readily releasable pool (RRP) of equally fusion-competent vesicles, suggesting that differences in the vesicles' proximity to Ca2+ channels underlie the biphasic secretory behavior. An intermediate pool in dynamic equilibrium with the RRP ensures rapid recruitment of release-ready vesicles after RRP depletion. Our results are discussed in terms of a refined model for secretion in chromaffin cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adrenal Glands / cytology*
  • Adrenal Glands / metabolism
  • Animals
  • Calcium / pharmacokinetics
  • Calcium Channels / physiology*
  • Chromaffin Cells / chemistry*
  • Chromaffin Cells / metabolism*
  • Cytoplasmic Granules / chemistry
  • Cytoplasmic Granules / metabolism*
  • Electric Conductivity
  • Electrophysiology
  • Exocytosis / physiology
  • Kinetics
  • Membrane Fusion / physiology
  • Membrane Potentials / physiology
  • Mice
  • Mice, Inbred Strains
  • Organ Culture Techniques
  • Photochemistry


  • Calcium Channels
  • Calcium