title: Elementary properties of CaV1.3 Ca(2+) channels expressed in mouse cochlear inner hair cells.
abstract: Mammalian cochlear inner hair cells (IHCs) are specialized to process developmental signals during immature stages and sound stimuli in adult animals. These signals are conveyed onto auditory afferent nerve fibres. Neurotransmitter release at IHC ribbon synapses is controlled by L-type Ca(V)1.3 Ca(2+) channels, the biophysics of which are still unknown in native mammalian cells. We have investigated the localization and elementary properties of Ca(2+) channels in immature mouse IHCs under near-physiological recording conditions. Ca(V)1.3 Ca(2+) channels at the cell pre-synaptic site co-localize with about half of the total number of ribbons present in immature IHCs. These channels activated at about 70 mV, showed a relatively short first latency and weak inactivation, which would allow IHCs to generate and accurately encode spontaneous Ca(2+) action potential activity characteristic of these immature cells. The Ca(V)1.3 Ca(2+) channels showed a very low open probability (about 0.15 at 20 mV: near the peak of an action potential). Comparison of elementary and macroscopic Ca(2+) currents indicated that very few Ca(2+) channels are associated with each docked vesicle at IHC ribbon synapses. Finally, we found that the open probability of Ca(2+) channels, but not their opening time, was voltage dependent. This finding provides a possible correlation between presynaptic Ca(2+) channel properties and the characteristic frequency/amplitude of EPSCs in auditory afferent fibres.
authors.affiliation: Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN, UK.
authors.forename: Valeria
authors.initials: V
authors.lastname: Zampini
authors.forename: Stuart L
authors.initials: SL
authors.lastname: Johnson
authors.forename: Christoph
authors.initials: C
authors.lastname: Franz
authors.forename: Neil D
authors.initials: ND
authors.lastname: Lawrence
authors.forename: Stefan
authors.initials: S
authors.lastname: Münkner
authors.forename: Jutta
authors.initials: J
authors.lastname: Engel
authors.forename: Marlies
authors.initials: M
authors.lastname: Knipper
authors.forename: Jacopo
authors.initials: J
authors.lastname: Magistretti
authors.forename: Sergio
authors.initials: S
authors.lastname: Masetto
authors.forename: Walter
authors.initials: W
authors.lastname: Marcotti
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D006199:Hair Cells, Auditory, Inner / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL
chemical_list: C485995:Cacna1d protein, mouse; D020746:Calcium Channels, L-Type; D002118:Calcium