FIGURE 2.

Model of an OHC bundle. (A) Geometry of a simulated hair bundle that contains three rows, with 29 stereocilia per row. The tallest stereocilia are nearly upright, whereas the shorter stereocilia are tilted toward the taller stereocilia. (B) There are three structural components: stereocilia, tip link (assembly), and horizontal connector. The channels are located at the upper end of each tip link. (C) The kinetic scheme used in the model for the MT channel has five closed (C) and five open (O) states, with the rate constants between C and O dependent on the mechanical stimulus and the transitions between each of the C (or O) states dependent on binding of one to four calcium ions. As Ca²⁺ binds to the channel, it requires an additional force, f_Ca, to open a channel, and the gating spring is released by the fixed amount, b₂.