Membrane tension in swelling and shrinking molluscan neurons

Area of Science:

• Cell Biology
• Neuroscience
• Biophysics

Background:

• Neurons experience significant volume and shape changes.
• Maintaining cell surface area is crucial for neuronal function and survival.
• The membrane tension hypothesis proposes a feedback mechanism for surface area homeostasis.

Purpose of the Study:

• To investigate the role of membrane tension in neuronal surface area homeostasis.
• To test the membrane tension hypothesis during cell swelling and shrinking.
• To examine the influence of cytoplasmic calcium on membrane tension regulation.

Main Methods:

• Measuring apparent membrane tension of Lymnaea neurons using membrane tether forces.
• Inducing cell swelling and shrinking using hypotonic and isotonic media.
• Utilizing BAPTA to chelate cytoplasmic calcium (Ca2+).
• Measuring membrane capacitance changes in voltage-clamped neurons.

Main Results:

• Neuronal swelling increased membrane tension, but steady-state tension was only moderately elevated.
• Shrinking neurons exhibited reduced membrane tension and membrane invagination.
• BAPTA-induced calcium depletion led to large, non-lytic tension surges during swelling.
• Membrane capacitance increased during swelling, indicating an increase in membrane area.
• Neurons survived tension surges even without calcium signaling.

Conclusions:

• The membrane tension hypothesis provides a framework for neuronal surface area homeostasis.
• Feedback regulation of membrane tension helps buffer against mechanical stress.
• Cytoplasmic calcium influences the regulation of membrane tension during swelling.
• Neurons possess a tension-sensing mechanism for recruiting membrane stores to prevent rupture.