The coupling between synaptic vesicles and Ca2+ channels determines fast neurotransmitter release |
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Authors: | Wadel Kristian Neher Erwin Sakaba Takeshi |
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Institution: | 1. Research Group Biophysics of Synaptic Transmission, Max Planck Institute for Biophysical Chemistry, Göttingen, 37077, Germany;2. Department of Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, Göttingen, 37077, Germany |
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Abstract: | In order to release neurotransmitter synchronously in response to a presynaptic action potential, synaptic vesicles must be both release competent and located close to presynaptic Ca2+ channels. It has not been shown, however, which of the two is the more decisive factor. We tested this issue at the calyx of Held synapse by combining Ca2+ uncaging and electrophysiological measurements of postsynaptic responses. After depletion of the synaptic vesicles that are responsible for synchronous release during action potentials, uniform elevation of intracellular Ca2+ by Ca2+ uncaging could still elicit rapid release. The Ca2+ sensitivity of remaining vesicles was reduced no more than 2-fold, which is insufficient to explain the slow-down of the kinetics of release (10-fold) observed during a depolarizing pulse. We conclude that recruitment of synaptic vesicles to sites where Ca2+ channels cluster, rather than fusion competence, is a limiting step for rapid neurotransmitter release in response to presynaptic action potentials. |
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