title: Prestin-driven cochlear amplification is not limited by the outer hair cell membrane time constant.
abstract: 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.
authors.affiliation: Department of Biomedical Science, University of Sheffield, Sheffield S102TN, UK.
authors.forename: Stuart L
authors.initials: SL
authors.lastname: Johnson
authors.forename: Maryline
authors.initials: M
authors.lastname: Beurg
authors.forename: Walter
authors.initials: W
authors.lastname: Marcotti
authors.forename: Robert
authors.initials: R
authors.lastname: Fettiplace
mesh_terms: D000818:Animals; D027321:Anion Transport Proteins / Q000502:physiology; D002118:Calcium / Q000502:physiology; D004553:Electric Conductivity; D005849:Gerbillinae; D018072:Hair Cells, Auditory, Outer / Q000502:physiology*; D006309:Hearing / Q000502:physiology; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000502:physiology*; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D009925:Organ of Corti / Q000166:cytology / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated / Q000502:physiology; D011487:Protein Conformation; D051381:Rats; D000076988:Sulfate Transporters; D013997:Time Factors
chemical_list: D027321:Anion Transport Proteins; D024642:Potassium Channels, Voltage-Gated; C409207:Slc26a5 protein, rat; D000076988:Sulfate Transporters; D002118:Calcium