FIGURE 15.

Striolar Type I hair cell bundle viewed from above with different deflection loadings. In these diagrams, each circle represents a stereocilium or kinocilium (designated K), with stereocilia without a tip-link are in white. Tip-link tension color-scales are shown to the right of each figure in terms of pN (piconewtons) force above a resting tension of 20 pN. The resting tension is produced by the molecular motors that hold the tension at a value just below channel open probability with the bundle at rest. Any stereocilium with an increased tip-link tension of 1.0 pN above resting is considered at 50% open probability. The Bundle to the left (A) is loaded with both fluid flow producing a drag force on the bundle and a point load on top of the kinocilium. All tip-links in this bundle are well above the 50% open probability tension and are considered open. The bundle to the right (B) is only loaded with a point force load on the kinocilium top, and with no fluid flow drag force loading. A large fraction of the tip-links around the periphery are well below the 50% open probability range. Those at the bottom are not tensioned at all. Only the central portion of the bundle has well opened tip-link channels. Tip-link tensions are shown after a full dynamic loading time period of 1 ms (Nam et al., 2005).