Releasable pools and the kinetics of exocytosis in adrenal chromaffin cells

Neuron. 1994 Nov;13(5):1119-29. doi: 10.1016/0896-6273(94)90050-7.


Using high resolution capacitance (Cm) measurement techniques, we mapped the kinetics of exocytosis evoked by brief (5-100 ms) depolarizations that activate voltage-dependent Ca2+ channels in rat adrenal chromaffin cells. After correcting the Cm signal for contributions from Na+ channel-gating charge movements, the initial kinetics of exocytosis were consistent with depolarization-triggered release occurring initially from an immediately releasable pool of only approximately 17 secretory vesicles. In contrast, repetitive application of longer depolarizations evoked release from a distinct, larger readily releasable pool of approximately 170 vesicles. Our results suggest that the secretory response of a chromaffin cell to an action potential is limited by the size of the immediately releasable pool rather than by a fusion mechanism that is slower than that at synapses.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adrenal Medulla / cytology
  • Adrenal Medulla / metabolism*
  • Animals
  • Calcium / physiology
  • Calcium Channels / physiology
  • Cell Degranulation / physiology
  • Culture Techniques
  • Dibucaine / pharmacology
  • Exocytosis*
  • Kinetics
  • Membrane Potentials
  • Rats


  • Calcium Channels
  • Dibucaine
  • Calcium