Synchronized Ca2+ signals mediated by Ca2+ action potentials in the hippocampal neuron network in vitro.
Periodic, synchronized Ca2+ signals appeared 30-120 min after the application of tetrodotoxin, 4-aminopyridine and Cs+, and became stable in interval (6-47s) for hours. The Ca2+ signals were accompanied by excitatory or inhibitory postsynaptic potentials (excitatory postsynaptic currents (EPSCs) for the former) and blocked by the simultaneous application of 6-cyano-7-nitroquinoxaline-2,3-dione and 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid or treatment with Ca2+ -free solution, nicardipine, or omega-conotoxin MVIIC (omegaCTX), but not with ryanodine, caffeine, thapsigargin or CPP alone. Nicardipine largely, but omegaCTX less, blocked Ca2+ action potentials or voltage pulse-induced Ca2+ currents at the cell soma, while omegaCTX completely blocked autaptic EPSCs. Ca2+ signals within a neuron occurred almost simultaneously in the cell soma and all the processes (> 200 microm), while the latency between Ca2+ signals of neighbouring neurons varied over hundreds of ms like that of Ca2 action potential induction from EPSPs. Ca2+ signals propagated in random directions throughout neural circuits. Thus, when Na+ and K+ channels are blocked, Ca2+ action potentials spontaneously occur somewhere in a neuron, eventually propagate via the cell soma to the presynaptic terminals and activate excitatory synaptic transmission, causing synchronized Ca2+ signals. The results further suggest that the axon of hippocampal neurones have the potential ability to convey coded information via Ca2+ action potentials.
Lu
F M
FM
Department of Physiology, School of Medicine, Nagoya University, Nagoya, 466-8550, Japan.
Kuba
K
K
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001683:Biological Clocks / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002586:Cesium / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism; D009415:Nerve Net / Q000502:physiology*; D009474:Neurons / Q000166:cytology / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology
D015220:Calcium Channels; D002586:Cesium; D013779:Tetrodotoxin; D015761:4-Aminopyridine; D002118:Calcium