Dendritic Ca2+ transients evoked by action potentials in rat dorsal cochlear nucleus pyramidal and cartwheel neurons.
Simultaneous fluorescence imaging and electrophysiologic recordings were used to investigate the Ca(2+) influx initiated by action potentials (APs) into dorsal cochlear nucleus (DCN) pyramidal cell (PC) and cartwheel cell (CWC) dendrites. Local application of Cd(2+) blocked Ca(2+) transients in PC and CWC dendrites, demonstrating that the Ca(2+) influx was initiated by dendritic Ca(2+) channels. In PCs, TTX eliminated the dendritic Ca(2+) transients when APs were completely blocked. However, the Ca(2+) influx could be partially recovered during an incomplete block of APs or when a large depolarization was substituted for the blocked APs. In CWCs, dendritic Ca(2+) transients evoked by individual APs, or simple spikes, were blocked by TTX and could be recovered during an incomplete block of APs or by a large depolarization. In contrast, dendritic Ca(2+) transients evoked by complex spikes, a burst of APs superimposed on a slow depolarization, were not blocked by TTX, despite eliminating the APs superimposed on the slow depolarization. These results suggest two different mechanisms for the retrograde activation of dendritic Ca(2+) channels: the first requires fast Na(+) channel-mediated APs or a large somatic depolarization, whereas the second is independent of Na(+) channel activation, requiring only the slow depolarization underlying complex spikes.
Molitor
Scott C
SC
Department of Bioengineering, University of Toledo, Toledo, Ohio 43606-3390, USA. smolitor@eng.utoledo.edu
Manis
Paul B
PB
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D048429:Cell Size / Q000502:physiology; D017626:Cochlear Nucleus / Q000166:cytology / Q000502:physiology*; D003712:Dendrites / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D015222:Sodium Channels / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D000779:Anesthetics, Local; D015220:Calcium Channels; D015222:Sodium Channels; D002104:Cadmium; D013779:Tetrodotoxin; D002118:Calcium