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Patch clamp studies of single intact secretory granules
A F Oberhauser1, J M Fernandez
1Department of Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota 55905.
Biophysical Journal
|November 1, 1993
Summary
Investigating secretory granule membranes revealed that intact granules have low conductance. Mechanical or electrical stress induced pore formation, mimicking exocytotic fusion pore behavior.
Area of Science:
- Cell Biology
- Biophysics
Background:
- Secretory granule membranes are implicated in exocytotic fusion.
- Proteins from granule membranes, when reconstituted, form ion channels, suggesting a role in the fusion pore structure.
Purpose of the Study:
- To investigate ion conductances in single secretory granules from beige mouse mast cells.
- To determine if granule membrane proteins form functional ion channels in intact granules.
- To compare the behavior of induced pores in granule membranes with observed exocytotic fusion pores.
Main Methods:
- Utilized the patch clamp technique to study ion conductances.
- Examined single isolated secretory granules from beige mouse mast cells.
- Applied mechanical tension and large voltage pulses to induce membrane breakdown.
Main Results:
- Intact granule membranes exhibited low conductance (< 50 pS) without spontaneous channel activity.
- Mechanical tension or voltage pulses induced rapid pore opening (approx. 1 nS conductance) with fluctuating behavior.
- The conductance patterns of mechanically/electrically induced pores closely resembled those of exocytotic fusion pores.
Conclusions:
- The study suggests that the earliest exocytotic fusion pore may form from the breakdown of a lipid bilayer, potentially during hemifusion.
- Findings challenge the direct role of pre-formed protein channels in the initial fusion pore formation.
- The behavior of induced pores provides a model for understanding the dynamic nature of the exocytotic fusion pore.