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This Article Full Text Full Text (PDF) All Versions of this Article: 92/5/2685    most recent 00267.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Manley, G. A. Articles by Köppl, C. Search for Related Content PubMed PubMed Citation Articles by Manley, G. A. Articles by Köppl, C.

Calcium Modulates the Frequency and Amplitude of Spontaneous Otoacoustic Emissions in the Bobtail Skink

Lehrstuhl für Zoologie, Technische Universität München, 85747 Garching, Germany; and The Auditory Laboratory, Physiology, School of Biomedical and Chemical Sciences, The University of Western Australia, Crawley, Western Australia, 6009, Australia

Submitted 18 March 2004; accepted in final form 16 April 2004

Active processes in the inner ear of lizards can be monitored using spontaneous otoacoustic emissions (SOAE) measured outside the eardrum. In the Australian bobtail lizard, SOAE are generated by an active motility process in the hair-cell bundle. This mechanism has been shown to be sensitive to the calcium-chelating agent 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid and is presumed to be related to the calcium-sensitive transduction-channel motor implicated in other nonmammalian hair cell systems. In studies of frog saccular and turtle auditory papillar hair cells in vitro, the frequency and amplitude of bundle oscillations depend on the concentration of calcium in the bathing solutions. In the present study, the calcium concentration in the endolymph was changed in vivo in the Australian bobtail lizard Tiliqua rugosa, and SOAE were monitored. Glass pipettes with large tips and containing different calcium concentrations in their fluids were introduced into scala media, and their contents were allowed to passively flow into the endolymph. Low calcium concentrations resulted in a downward shift in the frequency of SOAE spectral peaks and generally an increase in their amplitudes. Calcium concentrations >2 mM resulted in increases in frequency of SOAE peaks and generally a loss in amplitude. These frequency shifts were consistent with in vitro data on the frequencies and amplitudes of spontaneous oscillation of hair cell bundles and thus also implicate calcium ions in the generation of active motility in nonmammalian hair cells. The data also suggest that in this lizard species, the ionic calcium concentration in the cochlear endolymph is 1 mM.