Lateral diffusion anisotropy and membrane lipid/skeleton interaction in outer hair cells.

Area of Science:

• Cell Biology
• Biophysics
• Auditory Science

Background:

• The plasma membrane's lipid organization into domains influences its interaction with the underlying protein skeleton, affecting molecular mobility.
• Membrane fluidity is crucial for cellular functions and can be assessed using techniques like fluorescence recovery after photobleaching (FRAP).

Purpose of the Study:

• To analyze the two-dimensional pattern of lipid diffusion in the lateral plasma membrane of cochlear outer hair cells (OHCs).
• To investigate the influence of turgor pressure and the membrane skeleton on OHC membrane lipid mobility.

Main Methods:

• Utilized fluorescence recovery after photobleaching (FRAP) to measure lipid diffusion in isolated OHCs and intact temporal bone preparations.
• Analyzed the two-dimensional diffusion patterns of lipids in the OHC lateral membrane.
• Performed osmotic challenges to alter cell turgor pressure and observed effects on lipid diffusion.

Main Results:

• Membrane lipid mobility in OHCs is orthotropic, with faster diffusion along the cell's axial direction and slower diffusion circumferentially.
• Increased turgor pressure reduced axial diffusion but had minimal impact on circumferential diffusion.
• Lipid mobility in OHCs and inner hair cells within the intact organ was comparable, suggesting similar fluid membrane phases; supporting cells showed slower mobility.

Conclusions:

• The OHC plasma membrane skeleton, potentially spectrin filaments, influences lipid mobility, leading to orthotropic diffusion.
• The findings support the notion of similar, highly fluid membrane phases in both OHCs and inner hair cells within the intact cochlea.
• Differences in lipid mobility between hair cells and supporting cells may indicate distinct lipid compositions or cytoskeletal interactions.