Analysis of the dynamic behavior of the inner hair cell stereocilia by the finite element method

The motion of the inner hair cell (IHC) stereocilia, which results in tension in the tip links connected to mechanically gated ion channels, mediates the auditory transduction process. However, it is difficult to directly observe the motion of the stereocilia because of their minute dimensions and complex structure. In this study, to investigate such motion, a finite element method model of the tall, middle and short IHC stereocilia, including the tip and lateral links extending between the stereocilia, was constructed. By applying an analytically estimated fluid force caused by a stimulus of 60dB SPL at 500 Hz to the model, the dynamic behavior of the stereocilia was analyzed. Numerical results showed that the stereocilia moved in phase and that the maximum tensions of 2.5 fN and 2.1 fN occurred in the tip link connecting the tall and middle stereocilia and in the tip link connecting the middle and short stereocilia, respectively. By contrast, under the condition in which the lateral links were removed, maximum tension in the former increased to 11.6 fN, while that in the latter only increased to 2.3 fN. It was therefore suggested that the lateral links protect the MET channels located at taller stereocilia against large stimuli and subject the channels located in the same IHC to forces of similar size.