Shape bistability of a membrane neck: a toggle switch to control vesicle content release

Area of Science:

• Biophysics
• Cell Biology
• Membrane Dynamics

Background:

• Vesicle fusion with the plasma membrane is crucial for cellular processes.
• The intermediate state, or membrane neck, plays a key role in regulating content release.
• Understanding the dynamics and permeability of this neck is essential for deciphering cellular transport mechanisms.

Purpose of the Study:

• To investigate the shape dynamics and permeability of membrane necks connecting vesicles and the plasma membrane.
• To model the membrane neck as a lipid membrane tubule and analyze its stable configurations.
• To explore the potential of these membrane structures to act as conductivity microswitches in cellular processes.

Main Methods:

• Modeling the membrane neck as a lipid membrane tubule between two axisymmetric rings.
• Analyzing the stability of different tubule shapes (catenoidal and cylindrical) based on length and membrane properties.
• Measuring ionic conductivity to quantify the permeability of the distinct tubule shapes.
• Observing bistable behavior in membrane connections in macrophages.

Main Results:

• The membrane tubule exhibits two stable shapes: catenoidal (microtubule) and cylindrical (nanotubule).
• The ionic conductivity of these shapes differs by up to four orders of magnitude.
• Shape transitions occur rapidly (under a millisecond) near a critical length, controlled by tubule length.
• Bistable behavior of membrane connections was observed in macrophages.

Conclusions:

• The membrane neck's shape switching acts as a conductivity microswitch, regulating vesicle content release.
• This mechanism supports cellular processes such as "kiss-and-run" exocytosis.
• The findings provide a biophysical basis for understanding regulated exocytosis and membrane dynamics.