He, David Ph.D.

Biomedical Sciences

Department of Biomedical Sciences: Professor

Research

The outer hair cell (OHC) is one of two
kinds of receptor cells in the inner ear,
and plays a critical role in mammalian hearing. OHCs enhance basilar membrane motion through a local mechanical feedback process within the cochlea, termed the ‘cochlear amplifier’. It is generally believed that the basis of cochlear amplification is a voltage-dependent somatic length change of OHCs. In this scheme, receptor potentials produced by transducer current in response to acoustic stimulation provide the input to the cell’s motor activity. Consequently, the OHC is thought to perform two transducer functions, a conventional mechanoelectrical or forward transduction in the stereocilia, and a specialized electromechanical or reverse transduction in the basolateral membrane (see the image of scanning EM below). The research in my laboratory focuses on the forward and reverse transduction in OHCs. Recordings are made from isolated hair cells, cultured organ of Corti preparations, and hemicochlea, in conjunction with molecular, morphological and other novel techniques to investigate properties of these cells and their roles in cochlear functions in mammals. The laboratory is fully equipped to conduct experiments at the cellular level with novel techniques. It includes three setups for doing standard whole-cell patch-clamp experiments. All three setups are also equipped with opto-electronic systems that allow measuring cell/hair-bundle motion down to nanometer range.

1. Biophysics of electrically and mechanically induced somatic motility and stiffness of cochlear outer hair cells.
2. Mechanoelectrical transduction of cochlear hair cells.
3. Development of motility, ion channels, and ACh receptors of cochlear outer hair cells.
4. Physiology of cochlear supporting cells.

Sample Images and Movies

Mammalian OHCs are able to change their length upon direct electrical stimulation. The video segment shows an example of OHC motility when the cell in the microchamber (a suction pipette) is stimulated by Japanese folk music. The cell was isolated from the apical turn of a guinea pig cochlea.

Click the picture to view the MPG movie in a new window.

The video clip shows large hair-bundle motion of an adult gerbil OHC in response to membrane potential change. The recording was made from an OHC in the apical-turn of the cochlea. The bundle motion is driven by somatic motility.

Click the picture to view the AVI movie in a new window.

Measurements of voltage-dependent stiffness of OHCs under the whole cell voltage-clamp condition. A vibrating fiber with known stiffness is loaded onto the cell to determine the stiffness of the cell during length change. The image is modified from He and Dallos, 1999, PNAS.

 

 

A. Simultaneous recording of transducer currents of OHCs and basilar membrane motion in a gerbil hemicochlea preparation. Transducer currents are recorded under whole-cell voltage-clamp condition. Basilar membrane motion is measured by photodiode-based measurement system.B. An example of transducer currents and BM motion recorded from a gerbil basal turn cell. The a segment of responses is plotted in an expanded time scale in the insert. Upward motion of the BM motion toward the scala vestibuli produces a large inward current, which depolarizes the cell.