Figure 1.

Description of the hair cell stereocilia bundle from turtle auditory papilla. (A) Top view of five rows and seven columns of stereocilia bundle interconnected by side and tip links. (B) Side view of the hair bundle provides the kinematic components in its resting (left) and stimulated (right) configuration. (C) Ciliary tip and tip-link complex. The tip link, composed of CDH23 and PCDH15, is inserted into the upper dense region, whereas the other end is tethered into the lipid membrane. Tension on the tip link separates the membrane from the cytoskeleton. (D) Partitioned lipid membrane for the stereocilia tip. The red region could be tightly coupled to the stereocilia cytoskeleton (i.e., a bundle of actin filaments) through a cross-linker; blue indicates the membrane tented region into which the tip link inserts. A possible stiff region for the channels and the other proteins with radius of 3 nm is shown in purple. (E) Model responses to different-size step functions (first row) are indicated by different intensities of blue. Bundle force (second row), single tip-link force (third row), and membrane free-energy density at a point 3.5 nm from tip-link lower insertion (fourth row) are plotted. See Table 1 for the parameters used. See Fig. S7 for results obtained without considering the stiff protein region. To see this figure in color, go online.