Prestin-Driven Cochlear Amplification Is Not Limited by the Outer Hair Cell Membrane Time Constant

Summary

Outer hair cells (OHCs) provide amplification in the mammalian cochlea using somatic force generation underpinned by voltage-dependent conformational changes of the motor protein prestin. However, prestin must be gated by changes in membrane potential on a cycle-by-cycle basis and the periodic component of the receptor potential may be greatly attenuated by low-pass filtering due to the OHC time constant (τ _m), questioning the functional relevance of this mechanism. Here, we measured τ _m from OHCs with a range of characteristic frequencies (CF) and found that, at physiological endolymphatic calcium concentrations, approximately half of the mechanotransducer (MT) channels are opened at rest, depolarizing the membrane potential to near −40 mV. The depolarized resting potential activates a voltage-dependent K ⁺ conductance, thus minimizing τ _m and expanding the membrane filter so there is little receptor potential attenuation at the cell's CF. These data suggest that minimal τ _m filtering in vivo ensures optimal activation of prestin.

Highlights

► Cochlear amplification via prestin limited by outer hair cell (OHC) time constant ► Endolymph Ca ²⁺ opens half the transduction channels, depolarizing OHC to −40 mV ► Depolarization activates K ⁺ conductance, reduces time constant and expands filter ► Minimal membrane filtering in vivo ensures prestin activation over all frequencies