title: The resting transducer current drives spontaneous activity in prehearing mammalian cochlear inner hair cells.
abstract: Spontaneous Ca(2+)-dependent electrical activity in the immature mammalian cochlea is thought to instruct the formation of the tonotopic map during the differentiation of sensory hair cells and the auditory pathway. This activity occurs in inner hair cells (IHCs) during the first postnatal week, and the pattern differs along the cochlea. During the second postnatal week, which is before the onset of hearing in most rodents, the resting membrane potential for IHCs is apparently more hyperpolarized (approximately -75 mV), and it remains unclear whether spontaneous action potentials continue to occur. We found that when mouse IHC hair bundles were exposed to the estimated in vivo endolymphatic Ca(2+) concentration (0.3 mm) present in the immature cochlea, the increased open probability of the mechanotransducer channels caused the cells to depolarize to around the action potential threshold (approximately -55 mV). We propose that, in vivo, spontaneous Ca(2+) action potentials are intrinsically generated by IHCs up to the onset of hearing and that they are likely to influence the final sensory-independent refinement of the developing cochlea.
authors.affiliation: Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN, United Kingdom. s.johnson@sheffield.ac.uk
authors.forename: Stuart L
authors.initials: SL
authors.lastname: Johnson
authors.forename: Helen J
authors.initials: HJ
authors.lastname: Kennedy
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Holley
authors.forename: Robert
authors.initials: R
authors.lastname: Fettiplace
authors.forename: Walter
authors.initials: W
authors.lastname: Marcotti
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001703:Biophysics; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003051:Cochlea / Q000166:cytology* / Q000254:growth & development; D004096:Dihydrostreptomycin Sulfate / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004710:Endolymph / Q000378:metabolism; D005260:Female; D018684:Glycine Agents / Q000494:pharmacology; D006199:Hair Cells, Auditory, Inner / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects; D008297:Male; D040542:Mechanotransduction, Cellular / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D018408:Patch-Clamp Techniques; D010812:Physical Stimulation; D013331:Strychnine / Q000494:pharmacology
chemical_list: D018684:Glycine Agents; C045674:2',3'-O-(2,4,6-trinitro-cyclohexadienylidine)adenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D013331:Strychnine; D002118:Calcium; D004096:Dihydrostreptomycin Sulfate