Nonlinear calcium ion waves along actin filaments control active hair-bundle motility

Calcium ions (Ca²⁺) tune and control numerous diverse aspects of cochlear and vestibular physiological processes. This paper is focused on the Ca²⁺ control of mechanotransduction in sensory hair cells in the context of polyelectrolyte properties of actin filaments within the hair-bundles of inner ear. These actin filaments appear to serve as efficient pathways for the flow of Ca²⁺ ions inside stereocilia. We showed how this can be utilized for tuning of force-generating myosin motors. In an established model, we unified the Ca²⁺ nonlinear dynamics involved in the control of myosin adaptation motors with mechanical displacements of hair-bundles. The model shows that the characteristic time scales fit reasonably well with the available experimental data for spontaneous oscillations in the inner ear. This scenario promises to fill a gap in our understanding of the role of Ca²⁺ ions in the regulation of processes in the auditory cells of the inner ear.