Static material properties of the tectorial membrane: a summary

Area of Science:

• Otoacoustic emissions
• Biophysics
• Materials science

Background:

• The tectorial membrane (TM) is a critical component of the cochlea, acting as a polyelectrolyte gel.
• Its physical properties are intrinsically linked to its chemical, electrical, and osmotic characteristics.
• Understanding these properties is crucial for deciphering auditory function and dysfunction.

Purpose of the Study:

• To review, integrate, and interpret recent findings on the chemical, electrical, mechanical, and osmotic properties of isolated TM preparations.
• To elucidate the relationship between ion concentrations, pH, and TM dimensions.
• To validate the polyelectrolyte gel model for the TM.

Main Methods:

• Experiments using isolated TM preparations from alligator lizard, chick, and mouse.
• Manipulation of bath ion concentrations (calcium, sodium) and pH.
• Measurements of TM dimensions and electric potentials.
• Application of osmotic pressure and ionic strength variations.

Main Results:

• TM dimensions are sensitive to calcium (shrinks) and sodium (swells) concentrations, with competitive binding influencing conformation and mechanical properties.
• Sodium-induced swelling is specific and not replicated by other alkali metal cations.
• TM swelling occurs at pH < 6 or pH > 7, consistent with changes in fixed charge density.
• Osmotic pressure and ionic strength alterations affect TM dimensions as predicted by the polyelectrolyte gel model.

Conclusions:

• The tectorial membrane behaves as a polyelectrolyte gel whose properties are interdependent.
• Ion concentrations and pH significantly modulate TM dimensions and mechanical characteristics.
• A polyelectrolyte gel model accurately predicts the observed behavior of the TM in response to environmental changes.