Biophysical Properties of Cochlear Hair Cells

The goal of my research is to characterize the cellular mechanisms that contribute to sensory transduction and signal processing in the nervous system. My current experiments address the conductances underlying electrical resonance and its modulation in hair cells in the turtle auditory system. These hair cells are relatively undifferentiated, and a single cell type serves as both resonant detector of mechanical displacement, and target of efferent control. By understanding how frequency selectivity is achieved in reptiles, we can assess the applicability of these mechanisms to hearing in higher vertebrates, including man. Though a number of physiological and anatomical differences exist across vertebrates, some cellular processes may be quite general. Therefore, as an example, using turtle hair cells as a model, an increase in body temperature and a modest increase in conductance yield cells that resonate at the limits of human hearing.

The study of cochlear hair cells also offers a unique venue in which to explore the expression and modulation of a wide variety of ion channel phenotypes that are used to create variations in signal processing at a cellular level. The functional characteristics of hair cells vary systematically with position in the cochlea. By examining biophysical properties of cells of different resonant frequency we can begin to explore the mechanisms by which gene expression is modulated and maintained at the single channel level. It is also likely that in this context the significance of variations of channel phenotype and regulation may be apparent.

Currently a combination of patch clamp, microelectrode, and confocal imaging techniques are being used on solitary hair cells and the intact sensory epithelia of the turtle auditory and vestibular systems. Previous measurements of ionic currents are being extended and combined with imaging of ion-sensitive dyes to quantify the biophysical mechanisms that underlie frequency selectivity. These results are being used to construct a more complete description of the cell biology of hair cells.

Selected References

Goodman, M. B. and Art, J. J. (1996) Variations in the ensemble of potassium currents underlying resonance in turtle hair cells. Journal of Physiology 497.2: 395-412.

Jones, E.M.C., Gray-Keller, M., Art, J.J. and Fettiplace, R. (1999). The functional role of alternative splicing of Ca2+ -activated K+ channels in auditory hair cells. Annals of the New York Academy of Sciences 868:379-385.