INTRACELLULAR CALCIUM IN HAIR CELLS
Principal Investigator: Robert Fettiplace
Affiliation: University of Wisconsin
Abstract: The long-term objectives are to understand the cellular mechanisms of transduction in auditory hair cells and delineate the factors underlying the cochlea's tonotopic organization. Experiments will focus on transducer channel adaptation and hair bundle mechanics to define their regulation by Ca2+ and roles in frequency selectivity. A prime objective is to improve the speed of the mechanical stimulator and utilize different preparations and conditions to obtain accurate measures of the kinetics of transduction and active bundle motion. Hair cell responses will be measured in the isolated cochleae of both mammals and birds and will be combined with intracellular Ca2+ imaging. Specific aims are: (1) to record mechanotransducer currents in gerbil and rat hair cells before and after the onset of hearing, documenting the changes in kinetics and other properties with cochlear location; (2) to characterize single mechanotransducer channels and investigate their variation with cochlear location and modulation by Ca2+ and cyclic AMP, to provide a baseline for candidate channel proteins; (3) to measure the mechanical properties of hair bundles and search for spontaneous and active bundle motion in mammalian hair cells. The interaction between active bundle motion and outer hair cell contractility will be used to assess the roles of the two processes in amplification and frequency tuning in the intact mammalian cochlea. (4) to record mechanotransducer currents and measure hair bundle mechanics of short (outer) hair cells in the chick auditory papilla as a likely but unproven site where active hair bundle motion is used to augment frequency selectivity. Comparison with the properties of the mammalian hair bundles will provide insight into the evolution of cochlear amplification; (5) to measure and alter the concentration of Ca2+ in hair bundles and relate it to control of mechanotransducer channel adaptation and active hair bundle motion. The contributions of Ca2+ buffering and uptake into intracellular compartments, especially the mitochondria, to limit Ca2+ transients will be studied. Since hair cells experience large Ca2+ loads, disturbance of Ca2+ homeostasis may be a leading cause of injury. Ca2+ modulation of mechanotransducer channels is probably common to all hair cells and may be the site of irreversible damage during noise exposure, poisoning with ototoxic agents or aging. Loss of hearing with aging or over-stimulation is often restricted to high frequencies and is linked to degeneration of hair cells at one end of the cochlea. The work will address the reasons for this differential sensitivity by mapping the properties of transduction with location in the mammalian cochlea. It is hypothesized that the majority of Ca2+ enters the hair cells through the MT channels and the increased vulnerability of high frequency outer hair cells reflects a greater Ca2+ influx because of larger MT currents. Hearing impairment is the most common disabling sensory defect in humans. Severe to profound hearing loss, largely attributable to injury to the sensory hair cells, affects 1 in 1,000 newborns, and 60% of people older than 70 years have a hearing deficit of at least 25 dB. It has a range of causes, including genetic, noise or drug induced, as well as being age-related but the basic mechanisms of damage and cell death in most cases are not well understood. The work will address the mechanisms by documenting the mechanical and electrical properties of auditory hair cells and their modulation by calcium ions. We hypothesize that calcium overloading leading to mitochondrial dysfunction is a major route to cell damage.
Funding Period: 1992-01-01 - 2013-12-31
more information: NIH RePORT
- The transduction channel filter in auditory hair cellsAnthony J Ricci
Center for Neuroscience, Louisiana State University Medical Center, New Orleans, Louisiana 70112, USA
J Neurosci 25:7831-9. 2005....
- Localization of inner hair cell mechanotransducer channels using high-speed calcium imagingMaryline Beurg
INSERM U, Universite Victor Segalen Bordeaux, Hopital Pellegrin, France
Nat Neurosci 12:553-8. 2009..The observations, supported by theoretical simulations, suggest there are no functional mechanically sensitive transducer channels in first row stereocilia and imply the channels are present only at the bottom of the tip links...
- Theoretical conditions for high-frequency hair bundle oscillations in auditory hair cellsJong Hoon Nam
Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin, USA
Biophys J 95:4948-62. 2008..Spontaneous oscillations persisted, becoming very narrow-band, when the hair bundle was loaded with a tectorial membrane mass...
- The dimensions and composition of stereociliary rootlets in mammalian cochlear hair cells: comparison between high- and low-frequency cells and evidence for a connection to the lateral membraneDavid N Furness
Institute of Science and Technology in Medicine, Keele University, Keele, Staffordshire ST5 5BG, United Kingdom
J Neurosci 28:6342-53. 2008....
- The actions of calcium on hair bundle mechanics in mammalian cochlear hair cellsMaryline Beurg
INSERM U587, Universite Victor Segalen Bordeaux, Hopital Pellegrin, Bordeaux, France
Biophys J 94:2639-53. 2008..The significance of these results for cochlear transduction and amplification are discussed...
- A large-conductance calcium-selective mechanotransducer channel in mammalian cochlear hair cellsMaryline Beurg
Equipe Associée 3665 Université Victor Segalen Bordeaux 2, Institut National de la Sante et de la Recherche Medicale, Unité 587, Hopital Pellegrin, 33076 Bordeaux, France
J Neurosci 26:10992-1000. 2006..The results imply that the MT channel has properties possessed by few known candidates, and its diversity suggests expression of multiple isoforms...
- Ryanodine receptor localisation in the mammalian cochlea: an ultrastructural studyLisa Grant
Department of Physiology, University of Bristol, Bristol, UK
Hear Res 219:101-9. 2006..CICR may be involved in the control of calcium levels in the base of the inner hair cells and supporting cells, and in the cholinergic efferent response and motile behaviour of the outer hair cells...
- Active hair bundle movements in auditory hair cellsRobert Fettiplace
185 Medical Sciences Building, 1300, University Avenue, Madison, WI 53706, USA
J Physiol 576:29-36. 2006..This review summarizes evidence for active hair bundle motion and its connection to MT channel adaptation. Key factors for the hair bundle motor to play a role in the mammalian cochlea include the size and speed of force production...
- Depolarization of cochlear outer hair cells evokes active hair bundle motion by two mechanismsHelen J Kennedy
Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA
J Neurosci 26:2757-66. 2006..It is conceivable that the two processes can interact, a signal from the MET channels being capable of modulating the activity of the prestin motor...
- The concentrations of calcium buffering proteins in mammalian cochlear hair cellsCarole M Hackney
MacKay Institute of Communication and Neuroscience, School of Life Sciences, Keele University, Keele, Staffordshire ST5 5BG, United Kingdom
J Neurosci 25:7867-75. 2005..The high concentration of calcium buffer in outer hair cells, similar only to skeletal muscle, may protect against deleterious consequences of Ca2+ loading after acoustic overstimulation...
- Defining features of the hair cell mechanoelectrical transducer channelRobert Fettiplace
Department of Physiology, University of Wisconsin Medical School, 185 Medical Sciences Building, 1300 University Avenue, Madison, WI 53706, USA
Pflugers Arch 458:1115-23. 2009..The strengths and weaknesses of a TRP channel contender are discussed...