Rat Auditory Inner Hair Cell Mechanotransduction and Stereociliary Membrane Diffusivity Are Similarly Modulated by Calcium

The lipid bilayer plays a pivotal role in force transmission to many mechanically-gated channels. We developed the technology to monitor membrane diffusivity in order to test the hypothesis positing that Ca(2+) regulates open probability (P(o)) of cochlear hair cell mechanotransduction (MET) channels via the plasma membrane. The stereociliary membrane was more diffusive (9x) than the basolateral membrane. Elevating intracellular Ca(2+) buffering or lowering extracellular Ca(2+) reduced stereociliary diffusivity and increased MET P(o). In contrast, prolonged depolarization increased stereociliary diffusivity and reduced MET P(o). No comparable effects were noted for soma measurements. Although MET channels are located in the shorter stereocilia rows, both rows had similar baseline diffusivity and showed similar responses to Ca(2+) manipulations and MET channel blocks, suggesting that diffusivity is independent of MET. Together, these data suggest that the stereociliary membrane is a component of a calcium-modulated viscoelastic-like element regulating hair cell mechanotransduction.