IN VIVO ANALYSIS OF OUTER HAIR CELL MOTILITY

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During the last decade, many characteristics of OHC motility have been garnered through the in vitro (isolated cell) approach, including voltage dependence, subcellular site, nonlinearity, sensitivity, and phase. Despite such progress, it remains a difficult task to envision exactly how OHC motility might induce sharp tuning in the basilar membrane (BM), IHCs and single units. It is entirely possible that characteristics of OHC motility observed in vitro may differ from those within the normal in vivo milieu. A determination of in vivo characteristics in requisite for an accurate assessment of the influence of OHC motility on BM mechanics. OHC motility in contributing something special to peripheral auditory processing, but exactly what and how remain key questions which certainly require in vivo investigations. In this regard, it in proposed to analyze aspects of OHC motility in the intact cochlea. 1) Is it possible to measure the effects of the electrically evoked motility of a single OHC on basilar membrane notion? The in vivo measurement of BM motion during current injection in a single OHC may unequivocally demonstrate that OHC can influence the BH, and may permit the determination of the in vivo voltage-to-movement (V-M) function. 2) What in the voltage dependence of OHC nonlinear capacitance in vivo? OHCs possess a voltage dependent capacitance. Measures of nonlinear capacitance will provide insight into the voltage dependence of OHC motility in vivo, and should compliment data on the in vivo V-M function. 3) Does transient hypoxia alter the voltage dependence of the in vivo motility and nonlinear capacitance functions? It is clear that metabolic insult in vivo can dramatically and reversibly interfere with the normal functioning of the organ of Corti. A concomitant change in these OHC characteristics may provide evidence for OHC motility involvement. 4) Are OHCs coupled via gap junctions to supporting calls? A sensitive capacitive technique will be used to confirm the results of Zwislocki et al., which indicate that coupling exists. Communication between these cell types may provide an interesting mechanism for controlling OHC function. In sum, this type of in vivo analysis may help to understand how the OHC performs its duties, and further, may provide insight into the auditory pathologies which have as their basis OHC dysfunction.