Towards Understanding the Nature of the “Cochlear Amplifier”: Modeling the Physiology of the Outer Hair Cell

William Triffo, Rice University

The Organ of Corti (OC) is the cochlear structure responsible for transducing acoustic input into neural information. One component of the OC, the outer hair cell (OHC), is capable of undergoing axial deformation in response to electrical stimulus. This phenomenon, termed electromotility, enables the OHC to function as a mechanical amplifier of cochlear vibrations. Our ability to hear is thus dependent on properly functioning OHCs.

A unique feature of electromotility is its independence from direct metabolic input. While other motile cells, such as striated muscle, depend on direct coupling of adenosine triphosphate (ATP) hydrolysis to supply energy, the OHC's motion only depends on the transmembrane voltage potential. It is also known that the electromechanical transductive process occurs in the outer membrane of the OHC, and several models have been postulated to explain this effect. These include area-expansion and piezoelectric descriptions, as well as a model based on the flexoelectric effect, which describes deformations arising from electric field interactions with polarized membranes.

Current finite element models of the OHC model the cell as a trilaminate composite, utilizing shell elements for the outer membrane and subsurface cisternae, and plate models of the cortical lattice which capitalize on the observed domain architecture of the actin-spectrin network. To describe the electro-mechanical coupling in the outer membrane, such models rely on active strain interpretations of a proposed area expansion motor in the outer bilayer. Using a similar trilaminate structure, our current focus is to develop a model of the OHC using piezoelectric and flexoelectric effects as alterative explanations for OHC electromotility.

Abstract Author(s): William J. Triffo and Robert M. Raphael