This research will test the hypothesis that the functional development of the chick cochlea depends in part upon the gradual acquisition of a sharply-tuned electrical resonance arising from the action of voltage-dependent calcium current and calcium- dependent potassium current in the hair cell membrane. Thus, the onset and maturation of cochlear function ought to be correlated with the appearance of these ion channels in the hair cells. By describing the cellular basis of functional development, this investigation will add to our understanding of the cochlear filter mechanism, and so improve our ability to diagnose auditory dysfunction. Further, it is hoped that by examining the details of hair cell development it may prove possible to better understand how membrane differentiation is controlled, especially the possible role of electrical activity in that process. The electrical properties of individual isolated hair cells will be recorded using gigohm-seal suction electrode methods. Whole- cell voltage responses to injected current, and whole-cell current under voltage clamp will be recorded from each cell. In addition, various 'patch' configurations will be used to characterize the potassium channels in each cell. Hair cells will be isolated from selected regions of the cochlea and correlations drawn between cochlear position and electrical properties. Since cochlear function in the chick gradually improves from embryonic day 15 through hatching, the electrical properties of hair cells in the embryonic cochlea will be recorded to determine if electrical tuning develops concurrently. Finally, we will expand our studies to include short hair cells, the avian analogues of mammalian outer hair cells. Both electrical and mechanical properties of these cells will be studied. Of particular interest is the extent of electrical tuning in short hair cells, and any appearance of a mechanical correlate of that tuning.
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