Spontaneous otoacoustic emissions (SOAEs) are indicators of active processes in the inner ear and are found in all classes of land vertebrates. In the Australian bobtail lizard, earlier work showed that otoacoustic emissions are generated by an active motility process in the hair-cell bundle. This is likely to be driven by calcium-sensitive mechanisms implicated in other non-mammalian hair cell systems. If so, it should be fundamentally influenced by the extracellular calcium concentration. In in vitro studies, the rate of force generation in hair cell stereovilli is linked to the extracellular calcium concentration. In such preparations, low-calcium solutions, buffered by the calcium chelator BAPTA, were reported to change the frequency of hair cell bundle oscillations. In the present study, BAPTA was iontophoresed into the endolymph of the bobtail skink in vivo, and SOAEs were monitored. Application of BAPTA resulted in a prolonged downward shift in the frequency of individual SOAE spectral peaks. Recovery took more than 1 h, consistent with a slow clearance of BAPTA from endolymph. SOAE peak amplitudes were most often enhanced, suggesting there was no functional disruption of tip links. The direction and degree of frequency shifts were consistent with in vitroand in vivo data showing the effects of changing calcium concentrations in the endolymph directly.

1.
Ashmore JF: A fast motile response in guinea-pig outer hair cells: the cellular basis of the cochlear amplifier. J Physiol 1987;388:323–347.
2.
Assad JA, Hacohen N, Corey DP: Voltage dependence of adaptation and active bundle movement in bullfrog saccular hair cells. Proc Nat Acad Sci USA 1989;86:2918–2922.
3.
Assad JA, Shepherd GM, Corey DP: Tip-link integrity and mechanical transduction in vertebrate hair cells. Neuron 1991;7:985–994.
4.
Benser ME, Marquis RE, Hudspeth AJ: Rapid, active hair-bundle movements in hair cells from the bullfrog’s sacculus. J Neurosci 1996;16:5629–5643.
5.
Brownell WE, Bader CR, Bertrand D, de Ribaupierre Y: Evoked mechanical responses of isolated cochlear outer hair cells. Science 1985;227:194–196.
6.
Choe Y, Magnasco MO, Hudspeth AJ: A model for amplification of hair-bundle motion by cyclical binding of Ca2+ to mechanoelectrical-transduction channels. Proc Nat Acad Sci USA 1998;95:15321–15326.
7.
Crawford AC, Evans MG, Fettiplace R: Activation and adaptation of transducer currents in turtle hair cells. J Physiol 1989;419:405–434.
8.
Dallos P, Evans BN: High-frequency motility of outer hair cells and the cochlear amplifier. Science 1995;267:2006–2009.
9.
Eatock RA, Corey DP, Hudspeth AJ: Adaptation of mechanoelectrical transduction in hair cells of the bullfrog’s sacculus. J Neurosci 1987;7:2821–2836.
10.
Farris HE, LeBlanc CL, Goswami J, Ricci AJ: Probing the pore of the auditory hair cell mechanotransducer channel in turtle. J Physiol 2004;558:769–792.
11.
Fermin CD, Lychakov D, Campos A, Hara H, Sondag E, Jones T, Jones S, Taylor M, Meza-Ruiz G, Martin DS: Otoconia biogenesis, phylogeny, composition and functional attributes. Histol Histopath 1998;13:1103–1154.
12.
Ferrary E, Tran Ba Huy P, Roinel N, Bernard C, Amiel C: Calcium and the inner ear fluids. Acta Otolaryngol Suppl 1988;460:28–32.
13.
Fettiplace R: The role of calcium in hair cell transduction; in Corey DP, Roper SD (eds): Sensory Transduction. New York, Rockefeller University Press, 1992, pp 344–356.
14.
Fettiplace R, Ricci AJ, Hackney CM: Clues to the cochlear amplifier from the turtle ear. Trends Neurosci 2001;24:169–175.
15.
Freeman DM, Weiss TF: Species dependence of osmotic responses of the tectorial membrane: Implications of structure and biochemical composition. Midw Mtg Assoc Res in Otolaryngol 1995, p 188 (abstr 752)
16.
Furness DN, Hackney CM: Cross-links between stereocilia in the guinea pig cochlea. Hearing Res 1985;18:177–188.
17.
Hackney CM, Furness DN: Mechanotransduction in vertebrate hair cells: structure and function of the stereociliary bundle. Am J Physiol 1995;268:C1–C13.
18.
Hall JD, Betarbet S, Jaramillo F: Endogenous buffers limit the spread of free calcium in hair cells. Biophys J 1997;73:1243–1252.
19.
He DZ, Beisel KW, Chen L, Ding DL, Jia S, Fritzsch B, Salvi R: Chick hair cells do not exhibit voltage-dependent somatic motility. J Physiol 2003;546:511–520.
20.
Heller S, Bell AM, Denis CS, Choe Y, Hudspeth AJ: Parvalbumin 3 is an abundant Ca2+ buffer in hair cells. J Assoc Res Otolaryngol 2002;3:488–498.
21.
Hudspeth A: Mechanical amplification of stimuli by hair cells. Curr Opin Neurobiol 1997;7:480–486.
22.
Hudspeth A, Choe Y, Mahta AD, Martin P: Putting ion channels to work: Mechanoelectrical transduction, adaptation and amplification by hair cells. Proc Nat Acad Sci USA 2000;97:11765–11762.
23.
Jaramillo F: Signal transduction in hair cells and its regulation by calcium. Neuron 1995;15:1227–1230.
24.
Jaramillo F, Howard J, Hudspeth AJ: Calcium ions promote rapid mechanically evoked movements of hair bundles; in Dallos P, Geisler CD, Matthews JW, Ruggero MA, Steele CR (eds):The Mechanics and Biophysics of Hearing. Springer, Berlin 1990, pp 26–33.
25.
Kennedy HJ, Evans MG, Crawford AC, Fettiplace R: Fast adaptation of mechanoelectrical transducer channels in mammalian cochlear hair cells. Nature Neurosci 2003;6:832–836.
26.
Kirk DL: Effects of 4-aminopyridine on electrically evoked cochlear emissions and mechano-transduction in guinea pig outer hair cells. Hearing Res 2001;161:99–112.
27.
Köppl C, Forge A, Manley GA: Low density of membrane particles in auditory hair cells of lizards and birds suggests an absence of somatic motility. J Comp Neurol 2004;479:149–155.
28.
Köppl C, Manley GA: Spontaneous otoacoustic emissions in the bobtail lizard. I. General characteristics. Hearing Res 1993;71:157–169.
29.
Köppl C, Manley GA: Spontaneous otoacoustic emissions in the bobtail lizard. II. Interactions with external tones. Hearing Res 1994;72:159–170.
30.
Lumpkin EA, Hudspeth AJ: Regulation of free Ca2+ concentration in hair-cell stereocilia. J Neurosci 1998;18:6300–6318.
31.
Manley GA: Evidence for an active process and a cochlear amplifier in non-mammals. J Neurophysiol 2001;86:541–549.
32.
Manley GA, Kirk DL: The influence of injected AC and DC current on spontaneous otoacoustic emissions in the bobtail lizard. J Assoc Res Otolaryngol 2002;3:200–208.
33.
Manley GA, Kirk DL, Köppl C, Yates GK: In-vivo evidence for a cochlear amplifier in the hair-cell bundle of lizards. Proc Nat Acad Sci USA 2001;98:2826–2831.
34.
Manley GA, Köppl C: Phylogenetic development of the cochlea and its innervation. Curr Opin Neurobiol 1998;8:468–474.
35.
Manley GA, Köppl C, Sienknecht U: Calcium modulates the frequency and amplitude of spontaneous otoacoustic emissions in the bobtail skink. J Neurophysiol 2004;92:2685–2693.
36.
Marquis RE, Hudspeth AJ: Effects of extracellular Ca2+ concentration on hair-bundle stiffness and gating-spring integrity in hair cells. Proc Nat Acad Sci USA 1997;94:11923–11928.
37.
Martin P, Bozovic D, Choe Y, Hudspeth AJ: Spontaneous oscillation by hair bundles of the bullfrog’s sacculus. J Neurosci 2003;23:4533–4548.
38.
Martin P, Hudspeth AJ: Active hair-bundle movements can amplify a hair cell’s response to oscillatory mechanical stimuli. Proc Nat Acad Sci USA 1999;96:14306–14311.
39.
Martin P, Hudspeth AJ: Compressive nonlinearity in the hair bundle’s active response to mechanical stimulation. Proc Natl Acad Sci USA 2001;98:14386–14391.
40.
Meyer J, Furness DN, Zenner HP, Hackney CM, Gummer AW: Evidence for opening of hair-cell transducer channels after tip-link loss. J Neurosci 1998;18:6748–6756.
41.
Oberholtzer JC, Buettger C, Summers MC, Matschinsky FM: The 28-kDa calbindin-D is a major calcium-binding protein in the basilar papilla of the chick. Proc Natl Acad Sci USA 1988;85:3387–3390.
42.
Osborne MP, Comis SD, Pickles JO: Morphology and cross-linkage of stereocilia in the guinea-pig labyrinth examined without the use of osmium as a fixative. Cell Tiss Res 1984;237:43–48.
43.
Payan P, Borelli G, Priouzeau F, De Pontual H, Bœuf G, Mayer-Gostan N: Otolith growth in trout Oncorhynchus mykiss: supply of Ca2+ and Sr2+ to the saccular endolymph. J Exp Bio 2002;205:2687–2695.
44.
Pickles JO, Comis SD, Osborne MP: Cross-links between stereocilia in the guinea pig organ of Corti, and their possible relation to sensory transduction. Hearing Res 1984;15:103–112.
45.
Ricci AJ, Crawford AC, Fettiplace R: Mechanisms of active hair bundle motion in auditory hair cells. J Neurosci 2002;22:44–52.
46.
Ricci AJ, Crawford AC, Fettiplace R: Tonotopic variation in the conductance of the hair cell mechanotransducer channel. Neuron 2003;40:983–990.
47.
Ricci AJ, Fettiplace R: Calcium permeation of the turtle hair cell mechano-transducer channel and its relation to the composition of endolymph. J Physiol 1998;506:159–173.
48.
Ricci AJ, Wu YC, Fettiplace R: The endogenous calcium buffer and the time course of transducer adaptation in auditory hair cells. J Neurosci 1998;18:8261–8277.
49.
Salt AN, DeMott J: Time course of endolymph volume increase in experimental hydrops measured in vivo with an ionic volume marker. Hearing Res 1994;74:165–172.
50.
Santi P, Anderson CB: A newly identified surface coat on cochlear hair cells. Hearing Res 1987;27:47–65.
51.
Santos-Sacchi J, Dilger JP: Whole cell currents and mechanical responses of isolated outer hair cells. Hearing Res 1988;35:143–150.
52.
Shah DM, Freeman DM, Weiss TF: The osmotic response of the isolated, unfixed mouse tectorial membrane to isosmotic solution: effect of Na+, K+, and Ca2+ concentration. Hearing Res 1995;87:187–207.
53.
Vilfan A, Duke T: Two adaptation processes in auditory hair cells together can provide an active amplifier. Biophys J 2003;85:191–203.
54.
Wever EG: The Reptile Ear. Princeton University Press, New Jersey, 1978.
55.
Yamoah EN, Lumpkin EA, Dumont RA, Smith PJ, Hudspeth AJ, Gillespie PG: Plasma membrane Ca2+-ATPase extrudes Ca2+ from hair cell stereocilia. J Neurosci 1998;18:610–624.
56.
Zhao Y, Yamoah EN, Gillespie PG: Regeneration of broken tip links and restoration of mechanical transduction in hair cells. Proc Natl Acad Sci USA 1996;93:15469–15474.
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.