Models of otolithic membrane-hair cell bundle interaction

Transformation of the mechanical input in the chain: acceleration of otolithic membrane (OM)-displacement of the OM gel layer-deflection of hair cell bundle (HCB)-formation of the temporal pattern of polarization was studied using simplified analytical models of these stages of conversion of mechanical stimulus into the HCB electrical response. The dynamic behavior of an OM was modeled by a homogeneous viscoelastic (Kelvin-Voight body) model of the OM. Two alternative models of an 'HCB-surrounding gel' interaction corresponding to different types of the HCB were considered: (1) a model of stereocilia tip-link deformation in the case when the HCBs passively follow the gel deformation and (2) a model in which the tip-link dynamics is determined by an 'HCB-viscous fluid' interaction. It was shown that in the first model the 'HCB-OM gel' system functions as an accelerometer while in the second model it measures the time derivative of external acceleration. A simplified model of the temporal formation of cell depolarization is proposed and analyzed. Results of the modeling suggest that formation of a temporal response of the HCB to external acceleration occurs mainly due to two mutually correlated factors: the spatial dependence of gel displacement on the distance from a macular plane and the spatial distribution of stereocilia heights in the HCB.