title: Axon initial segment Ca2+ channels influence action potential generation and timing.
abstract: Although action potentials are typically generated in the axon initial segment (AIS), the timing and pattern of action potentials are thought to depend on inward current originating in somatodendritic compartments. Using two-photon imaging, we show that T- and R-type voltage-gated Ca(2+) channels are colocalized with Na(+) channels in the AIS of dorsal cochlear nucleus interneurons and that activation of these Ca(2+) channels is essential to the generation and timing of action potential bursts known as complex spikes. During complex spikes, where Na(+)-mediated spikelets fire atop slower depolarizing conductances, selective block of AIS Ca(2+) channels delays spike timing and raises spike threshold. Furthermore, AIS Ca(2+) channel block can decrease the number of spikelets within a complex spike and can even block single, simple spikes. Similar results were found in cortex and cerebellum. Thus, voltage-gated Ca(2+) channels at the site of spike initiation play a key role in generating and shaping spike bursts.
authors.affiliation: Vollum Institute and Oregon Hearing Research Center, Oregon Health and Science University, Portland, OR 97239, USA. benderke@ohsu.edu
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Bender
authors.forename: Laurence O
authors.initials: LO
authors.lastname: Trussell
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001369:Axons / Q000378:metabolism* / Q000648:ultrastructure; D015220:Calcium Channels / Q000378:metabolism*; D020908:Calcium Channels, R-Type / Q000378:metabolism; D020747:Calcium Channels, T-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D017626:Cochlear Nucleus / Q000166:cytology / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology; D051379:Mice; D008813:Mice, Inbred ICR; D008822:Mice, Transgenic; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000378:metabolism; D013997:Time Factors
chemical_list: D015220:Calcium Channels; D020908:Calcium Channels, R-Type; D020747:Calcium Channels, T-Type; D015222:Sodium Channels