Sensory hair cells in auditory and vestibular organs rely on active mechanisms to achieve high sensitivity and frequency selectivity. Recent experimental studies have documented self-sustained oscillations in hair cells of lower vertebrates on two distinct levels. First, the hair bundle can undergo spontaneous mechanical oscillations. Second, somatic electric voltage oscillations across thebasolateral membrane of the hair cell have been observed. We develop a biophysical model of the bullfrog's saccular hair cell consisting of two compartments, mechanical and electrical, to study how the mechanical and the voltage oscillations interact to produce coherent self-sustained oscillations and how this interaction contributes to the overall sensitivity and selectivity of the hair cell. The model incorporates nonlinear mechanical stochastic hair bundle system coupled bi-directionally to a Hodgkin-Huxley type system describing somatic ionic currents. We isolate regions of coherent spontaneous oscillations in the parameter space of the model and then study how coupling between compartments affects sensitivity of the hair cell to external mechanical perturbations. We show that spontaneous electrical oscillations may enhance significantly the sensitivity and selectivity of the hair cell.
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