Role of different types of Ca2+ channels and a reticulum-like Ca2+ pump in neurotransmitter release.
The factors controlling the Ca2+ concentration directly responsible for triggering acetylcholine (ACh) release were investigated at an identified neuro-neuronal synapse of the Aplysia buccal ganglion. The types of presynaptic voltage-gated Ca2+ channels associated with transmitter release were determined by using selective blockers such as nifedipine, omega-conotoxin and a partially purified extract from the venom of a funnel web spider (FTx). L-type, N-type and P-type Ca2+ channels are present in the presynaptic neuron. The influx of Ca2+ through both N- and P-types induces the release of ACh whereas Ca2+ flowing through L-type channels modulates the duration of the presynaptic action potential by controlling the Ca(2+)-dependent K+ current. tBuBHQ, a blocker of the reticulum Ca2+ pump, induces a potentiation of evoked release without modifying the presynaptic Ca2+ influx. This seems to indicate that a part of the Ca2+ entering the presynaptic terminal through N- and P-type Ca2+ channels is sequestered in a presynaptic reticulum-like Ca2+ buffer preventing these ions from contributing to ACh release. To exert its control, this Ca2+ buffer must be located close to both the presynaptic Ca2+ channels and the transmitter release mechanism.
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Laboratoire de Neurobiologie Cellulaire et Moléculaire, CNRS, Gif-sur-Yvette, France.
Baux
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Tauc
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D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001048:Aplysia; D002021:Buffers; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D009994:Osmolar Concentration; D017729:Presynaptic Terminals / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013569:Synapses / Q000502:physiology
D002021:Buffers; D015220:Calcium Channels; D018377:Neurotransmitter Agents; D000252:Calcium-Transporting ATPases; D009543:Nifedipine; D000109:Acetylcholine