title: The number and organization of Ca2+ channels in the active zone shapes neurotransmitter release from Schaffer collateral synapses.
abstract: Fast synaptic transmission requires tight colocalization of Ca(2+) channels and neurotransmitter vesicles. It is generally thought that Ca(2+) channels are expressed abundantly in presynaptic active zones, that vesicles within the same active zone have similar release properties, and that significant vesicle depletion only occurs at synapses with high release probability. Here we show, at excitatory CA3→CA1 synapses in mouse hippocampus, that release from individual vesicles is generally triggered by only one Ca(2+) channel and that only few functional Ca(2+) channels may be spread in the active zone at variable distances to neighboring neurotransmitter vesicles. Using morphologically realistic Monte Carlo simulations, we show that this arrangement leads to a widely heterogeneous distribution of release probability across the vesicles docked at the active zone, and that depletion of the vesicles closest to Ca(2+) channels can account for the Ca(2+) dependence of short-term plasticity at these synapses. These findings challenge the prevailing view that efficient synaptic transmission requires numerous presynaptic Ca(2+) channels in the active zone, and indicate that the relative arrangement of Ca(2+) channels and vesicles contributes to the heterogeneity of release probability within and across synapses and to vesicle depletion at small central synapses with low average release probability.
authors.affiliation: Synaptic Physiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-3701, USA. scimemia@ninds.nih.gov
authors.forename: Annalisa
authors.initials: A
authors.lastname: Scimemi
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Diamond
mesh_terms: D000818:Animals; D056547:CA1 Region, Hippocampal / Q000378:metabolism; D056654:CA3 Region, Hippocampal / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D019706:Excitatory Postsynaptic Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D008959:Models, Neurological; D009010:Monte Carlo Method; D009474:Neurons / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D013569:Synapses / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D018377:Neurotransmitter Agents