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Does BAPTA leave outer hair cell transduction channels closed?
P M Sellick1, D L Kirk, R Patuzzi
1The Auditory Laboratory, Discipline of Physiology, School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Nedlands, WA 6009, Australia. psellick@cyllene.uwa.edu.au
Hearing Research
|January 16, 2007
Summary
Reducing calcium in the cochlea with BAPTA lowers cochlear microphonic (CM) and increases endolymphatic potential (EP). This suggests calcium ions are crucial for mechano-electrical transduction in outer hair cells.
Area of Science:
- Oto-neuroscience
- Auditory physiology
- Cellular electrophysiology
Background:
- Calcium ions play a critical role in auditory hair cell function.
- The precise mechanism of mechano-electrical transduction in outer hair cells is still under investigation.
Purpose of the Study:
- To investigate the role of calcium ions in cochlear function.
- To explore the effect of calcium reduction on cochlear microphonics and endolymphatic potential.
Main Methods:
- Iontophoresis of the calcium chelator BAPTA into the guinea pig cochlea's scala media.
- Measurement of cochlear microphonics (CM) and endolymphatic potential (EP) using double-barreled pipettes.
- Controlled diffusion of BAPTA in separate experimental series.
Main Results:
- BAPTA application significantly reduced low-frequency CM and elevated CAP threshold.
- Current passed through BAPTA-filled pipettes caused a sustained increase in EP.
- Results confirmed a relationship between EP increase and decreased CM, indicating a causal link.
Conclusions:
- Lowering endolymphatic Ca2+ concentration with BAPTA inhibits mechano-electrical transduction in outer hair cells.
- This inhibition likely closes transduction channels, increasing outer hair cell resistance and EP.
- Findings support a model where stereocilia tension opens hair cell transduction channels.
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