Docked granules, the exocytic burst, and the need for ATP hydrolysis in endocrine cells

Neuron. 1995 Nov;15(5):1085-96. doi: 10.1016/0896-6273(95)90097-7.


Ca(2+)-triggered exocytosis was studied in single rat melanotrophs and bovine chromaffin cells by capacitance measurements. Sustained exocytosis required MgATP, but even in the absence of MgATP, Ca2+ could trigger exocytosis of 2700 granules in a typical melanotroph and of 840 granules in a chromaffin cell. Granules undergoing ATP-independent exocytosis were similar in number to those appearing docked to the plasmalemma in quickly frozen unfixed sections (3300 in a melanotroph and 830 in a chromaffin cell). Most exocytosis required tens of seconds, but a small pool of granules was released in tens of milliseconds. Evidently, only a small subset of docked granules is rapidly releasable. We suggest that, temporally, the last ATP-dependent step in exocytosis is closely associated with docking and that docked granules reach fusion competence only after subsequent steps.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism*
  • Adenosine Triphosphate / pharmacology
  • Adrenal Glands / metabolism
  • Adrenal Glands / ultrastructure
  • Animals
  • Calcium / pharmacology
  • Cattle
  • Chromaffin System / metabolism*
  • Chromaffin System / ultrastructure
  • Cytoplasmic Granules / metabolism*
  • Exocytosis* / drug effects
  • Hydrolysis
  • Melanocyte-Stimulating Hormones / metabolism
  • Pituitary Gland / metabolism*
  • Pituitary Gland / ultrastructure
  • Rats


  • Adenosine Triphosphate
  • Melanocyte-Stimulating Hormones
  • Calcium