Outer hair cells (OHCs) in the mammalian cochlea are inhibited by the release of acetylcholine (ACh) from efferent neurons. An analogous inhibitory mechanism is found in all vertebrate inner ears. Inhibition results from the activation of small-conductance calcium-dependent (SK) potassium channels. The hair cell's ACh receptor (AChR) is a ligand-gated cation channel whose nicotinic subunits, alpha9 and alpha10, have significant calcium permeability in functional expression studies. Thus, a compelling argument exists that calcium influx through the hair cell AChR directly activates SK channels. An unresolved question is whether the nearby synaptic cistern might release additional calcium. If so, under what conditions does calcium release play a significant role? What molecular mechanisms couple the AChR to the synaptic cistem? In this proposal we will employ biophysical and molecular genetic approaches to tackle this question in both avian and mammalian hair cells. Pharmacological agents that alter calcium store function will be applied during voltage-clamp recording from hair cells (with control experiments on alpha9/alpha10 expressed in oocytes). These treatments will be used during application of ACh to isolated hair cells, or while stimulating ACh release from efferent synaptic terminals in an excised organ of Corti preparation. Similar studies will be conducted on hair cells of the crooked neck dwarf chicken that lacks functional type 1 Ryan dine receptors. Transgenic mice will be generated and tested to probe AChR coupling to downstream signals. How is inhibition affected when so-called 'gain of function' AChRs are present? Does excess calcium influx through such 'super receptors' alter presumptive store-dependent components of the cholinergic response? In contrast, how is efferent input and the cholinergic response altered when hair cell AChRs are calcium irnpermeant? If inhibition persists without calcium influx, then other signaling, through conformational coupling or the generation of IP3, must be investigated. Emerging evidence suggests that ryanodine- and IP3-sensitive stores may predominate in hair cells from different regions of the cochlea. Finally, as our studies on calcium stores progress, new transgenic manipulations will be designed to directly test emerging hypotheses of signaling within the hair cell. These studies will add to our basic knowledge of calcium metabolism in hair cells. Calcium excitotoxicity could be instrumental in hair cell loss following trauma and throughout presbycusis.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC001508-15
Application #
7105469
Study Section
Auditory System Study Section (AUD)
Program Officer
Donahue, Amy
Project Start
1992-09-30
Project End
2009-08-31
Budget Start
2006-09-01
Budget End
2007-08-31
Support Year
15
Fiscal Year
2006
Total Cost
$638,754
Indirect Cost
Name
Johns Hopkins University
Department
Otolaryngology
Type
Schools of Medicine
DUNS #
001910777
City
Baltimore
State
MD
Country
United States
Zip Code
21218
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Boero, Luis E; Castagna, Valeria C; Di Guilmi, Mariano N et al. (2018) Enhancement of the Medial Olivocochlear System Prevents Hidden Hearing Loss. J Neurosci 38:7440-7451
Zachary, Stephen; Nowak, Nathaniel; Vyas, Pankhuri et al. (2018) Voltage-Gated Calcium Influx Modifies Cholinergic Inhibition of Inner Hair Cells in the Immature Rat Cochlea. J Neurosci 38:5677-5687
Moglie, Marcelo J; Fuchs, Paul A; Elgoyhen, Ana Belén et al. (2018) Compartmentalization of antagonistic Ca2+ signals in developing cochlear hair cells. Proc Natl Acad Sci U S A 115:E2095-E2104
Boffi, Juan Carlos; Marcovich, Irina; Gill-Thind, JasKiran K et al. (2017) Differential Contribution of Subunit Interfaces to ?9?10 Nicotinic Acetylcholine Receptor Function. Mol Pharmacol 91:250-262
Wu, Ping-Feng; Chuang, Chien; Su, Chin-Fang et al. (2016) High minimum inhibitory concentration of imipenem as a predictor of fatal outcome in patients with carbapenem non-susceptible Klebsiella pneumoniae. Sci Rep 6:32665
Fuchs, P A; Glowatzki, E (2015) Synaptic studies inform the functional diversity of cochlear afferents. Hear Res 330:18-25
Rohmann, Kevin N; Wersinger, Eric; Braude, Jeremy P et al. (2015) Activation of BK and SK channels by efferent synapses on outer hair cells in high-frequency regions of the rodent cochlea. J Neurosci 35:1821-30
Goutman, Juan D; Elgoyhen, A Belén; Gómez-Casati, María Eugenia (2015) Cochlear hair cells: The sound-sensing machines. FEBS Lett 589:3354-61
Zachary, Stephen Paul; Fuchs, Paul Albert (2015) Re-Emergent Inhibition of Cochlear Inner Hair Cells in a Mouse Model of Hearing Loss. J Neurosci 35:9701-6

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