Role of nonlinear localized Ca2+ pulses along microtubules in tuning the mechano–sensitivity of hair cells

This paper aims to provide an overview of the polyelectrolyte model and the current understanding of the creation and propagation of localized pulses of positive ions flowing along cellular microtubules. In that context, Ca2+ ions may move freely on the surface of microtubule along the protofilament axis, thus leading to signal transport. Special emphasis in this paper is placed on the possible role of this mechanism in the function of microtubule based kinocilium, a component of vestibular hair cells of the inner ear. We discuss how localized pulses of Ca2+ ions play a crucial role in tuning the activity of dynein motors, which are involved in mechano–sensitivity of the kinocilium. A prevailing notion holds that the concentration of Ca2+ ions around the microtubules within the kinocilium represents the control parameter for Hopf bifurcation. Therefore, a key feature of this mechanism is that the velocities of these Ca2+ pulses be sufficiently high to exert control at acoustic frequencies.