The Journal of Membrane Biology

, Volume 133, Issue 1, pp 61–75

Exocytotic fusion pores exhibit semi-stable states

  • Michael J. Curran
  • Fredric S. Cohen
  • Douglas E. Chandler
  • Peter J. Munson
  • Joshua Zimmerberg
Articles

DOI: 10.1007/BF00231878

Cite this article as:
Curran, M.J., Cohen, F.S., Chandler, D.E. et al. J. Membarin Biol. (1993) 133: 61. doi:10.1007/BF00231878

Summary

Rapid-freezing/freeze-fracture electron microscopy and whole-cell capacitance techniques were used to study degranulation in peritoneal mast cells of the rat and the mutant beige mouse. These studies allowed us to create a time-resolved picture for fusion pore formation. After stimulation, a dimple in the plasma membrane formed a small contact area with the secretory granule membrane. Within this zone of apposition no ordered proteinaceous specializations were seen. Electrophysiological technique measured a small fusion pore which widened rapidly to 1 nS. Thereafter, the fusion pore remained at semi-stable conductances between 1 and 20 nS for a wide range of times, between 10 and 15,000 msec. These conductances correspond to pore diameters 25–36 nm. Ultrastructural data confirmed small pores of hourglass morphology, composed of biological membrane coplanar with both the plasma and granular membranes. Later, the fusion pore rapidly increased in conductance, consistent with the observed morphology of omega-figures. The hallmarks of channel-like behavior, instantaneous jumps in pore conductance between defined levels, and sharp peaks in histograms of conductance dwell-time, were not seen. Since the morphology of small pores shows contiguous fracture planes, the electrical data represent pores that contain lipid. These combined morphological and electrophysiological data are consistent with a lipid/protein complex mediating both the initial and later stages of membrane fusion.

Key Words

membranes mast cells secretion electrophysiology freeze-fracture exocytosis 

Copyright information

© Springer-Verlag New York Inc. 1993

Authors and Affiliations

  • Michael J. Curran
    • 1
  • Fredric S. Cohen
    • 3
  • Douglas E. Chandler
    • 4
  • Peter J. Munson
    • 2
  • Joshua Zimmerberg
    • 1
  1. 1.Laboratory of Theoretical and Physical Biology, National Institute of Child Health and Human DevelopmentBethesda
  2. 2.Analytical Biostatistics Section, Division of Computer Research and TechnologyNational Institutes of HealthBethesda
  3. 3.Department of PhysiologyRush Medical CollegeChicago
  4. 4.Department of ZoologyArizona State UniversityTempe
  5. 5.National Institutes of HealthBethesda