title: Burst activity and ultrafast activation kinetics of CaV1.3 Ca²⁺ channels support presynaptic activity in adult gerbil hair cell ribbon synapses.
abstract: Auditory information transfer to afferent neurons relies on precise triggering of neurotransmitter release at the inner hair cell (IHC) ribbon synapses by Ca²⁺ entry through CaV1.3 Ca²⁺ channels. Despite the crucial role of CaV1.3 Ca²⁺ channels in governing synaptic vesicle fusion, their elementary properties in adult mammals remain unknown. Using near-physiological recording conditions we investigated Ca²⁺ channel activity in adult gerbil IHCs. We found that Ca²⁺ channels are partially active at the IHC resting membrane potential (-60 mV). At -20 mV, the large majority (>70%) of Ca²⁺ channel first openings occurred with an estimated delay of about 50 μs in physiological conditions, with a mean open time of 0.5 ms. Similar to other ribbon synapses, Ca²⁺ channels in IHCs showed a low mean open probability (0.21 at -20 mV), but this increased significantly (up to 0.91) when Ca²⁺ channel activity switched to a bursting modality. We propose that IHC Ca²⁺ channels are sufficiently rapid to transmit fast signals of sound onset and support phase-locking. Short-latency Ca²⁺ channel opening coupled to multivesicular release would ensure precise and reliable signal transmission at the IHC ribbon synapse.
authors.affiliation: Department of Biomedical Science, University of Sheffield, 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: Marlies
authors.initials: M
authors.lastname: Knipper
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Holley
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: D000818:Animals; D020746:Calcium Channels, L-Type / Q000502:physiology*; D005849:Gerbillinae; D006199:Hair Cells, Auditory, Inner / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D012964:Sodium / Q000502:physiology; D013569:Synapses / Q000502:physiology*
chemical_list: D020746:Calcium Channels, L-Type; D012964:Sodium