The development, distribution and density of the plasma membrane calcium ATPase 2 calcium pump in rat cochlear hair cells

Authors

  • Qingguo Chen,

    1. Department of Otolaryngology – Head and Neck Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
    2. Department of Neuroscience, University of Wisconsin Medical School, 1300 University Avenue, Madison, USA
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    • Q.C. and S.M. contributed equally to this work.

  • Shanthini Mahendrasingam,

    1. Institute for Science and Technology in Medicine, School of Life Sciences, Keele University, Keele, Staffordshire, UK
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    • Q.C. and S.M. contributed equally to this work.

  • Jacqueline A. Tickle,

    1. Institute for Science and Technology in Medicine, School of Life Sciences, Keele University, Keele, Staffordshire, UK
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  • Carole M. Hackney,

    1. Department of Biomedical Science, University of Sheffield, Sheffield, UK
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  • David N. Furness,

    1. Institute for Science and Technology in Medicine, School of Life Sciences, Keele University, Keele, Staffordshire, UK
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  • Robert Fettiplace

    1. Department of Neuroscience, University of Wisconsin Medical School, 1300 University Avenue, Madison, USA
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Dr R. Fettiplace, as above.
E-mail: fettiplace@physiology.wisc.edu

Abstract

Calcium is tightly regulated in cochlear outer hair cells (OHCs). It enters mainly via mechanotransducer (MT) channels and is extruded by the plasma membrane calcium ATPase (PMCA)2 isoform of the PMCA, mutations in which cause hearing loss. To assess how pump expression matches the demands of Ca2+ homeostasis, the distribution of PMCA2 at different cochlear locations during development was quantified using immunofluorescence and post-embedding immunogold labeling. The PMCA2 isoform was confined to stereociliary bundles, first appearing at the base of the cochlea around post-natal day (P)0 followed by the middle and then the apex by P3, and was unchanged after P8. The developmental appearance matched the maturation of the MT channels in rat OHCs. High-resolution immunogold labeling in adult rats showed that PMCA2 was distributed along the membranes of all three rows of OHC stereocilia at similar densities and at about a quarter of the density in inner hair cell stereocilia. The difference between OHCs and inner hair cells was similar to the ratio of their MT channel resting open probabilities. Gold particle counts revealed no difference in PMCA2 density between low- and high-frequency OHC bundles despite larger MT currents in high-frequency OHCs. The PMCA2 density in OHC stereocilia was determined in low- and high-frequency regions from calibration of immunogold particle counts as 2200/μm2 from which an extrusion rate of ∼200 ions/s per pump was inferred. The limited ability of PMCA2 to extrude the Ca2+ load through MT channels may constitute a major cause of OHC vulnerability and high-frequency hearing loss.

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