Cochlear hair bundle dynamics: modeling calcium effects and row-wise interactions

Abstract

External vibrations cause the eardrum to oscillate, resulting in the excitation of the sensory structures of the cochlea. In this talk, we focus on the hair bundles (HBs) of the outer hair cells situated inside the cochlea. These bundles, protruding from the cells, convert mechanical motion into electrical currents. Experimental observations reveal that the calcium concentration inside the stereocilia (hair-like structures that comprise the HB) influences current adaptation. This regulation impacts shifts of the curve, sensitivity, and active range of bundles. We aim to mechanistically understand the intracellular calcium effects by adjusting the adaptation complex in our HB model. We modified model parameters to match experimental data on current, bundle displacement, and shift trends at different calcium concentrations. This involved increasing the adaptation stiffness, stall force, stereocilia pivot, and gating stiffness. A stiffer adaptation spring reduces ion-channel reclosure, affecting the steady-state response. A higher stall force lessens the effective force on the adaptation complex, replicating experimental observations. Unlike the other properties, pivot, and gating stiffness likely do not depend on calcium concentration. Therefore, we will conduct error minimization analyses to identify adaptation complex properties while maintaining constant pivot and gating stiffness across calcium concentrations. Work supported by NIH grant NIH-NIDCD-R01 04084.