title: Ca2+ dynamics at the frog motor nerve terminal.
abstract: Rises in free [Ca2+]i in response to various tetanic stimuli (Ca2+ transient) in frog motor nerve terminals were measured by recording fluorescence changes of Ca2+ indicators and analyzed in relation to short-term synaptic plasticity. Ca2+ transients reached a plateau after 10-20 impulses at 100 Hz and decayed in a three-exponential manner, in which the fast component was predominant. The plateau and fast component of the Ca2+ transient were elevated infralinearly with an increase in tetanus frequency. Computer simulation showed that the Ca2+ transients estimated from fluorescence changes faithfully reflect the true changes in [Ca2+]i except for the initial 20 ms. A slow Ca2+ chelator, EGTA, loaded into the nerve terminal, decreased the magnitude of both the fast and slow components of facilitation of transmitter release and the time constant of the former. A fast Ca2+ chelator, BAPTA, decreased the magnitude of fast facilitation but slightly increased its time constant. These results suggest that Ca2+ transients in the frog motor nerve terminals are primarily caused by Ca2+ entry and are dissipated by three components, in which the rate of the fast component is equivalent to that of free Ca2+ diffusion. The residual Ca2+ in the nerve terminals after stimulation accounts for the fast component of facilitation.
authors.affiliation: Department of Physics, School of Science, Nagoya University, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Suzuki
authors.forename: M
authors.initials: M
authors.lastname: Osanai
authors.forename: M
authors.initials: M
authors.lastname: Murase
authors.forename: N
authors.initials: N
authors.lastname: Suzuki
authors.forename: K
authors.initials: K
authors.lastname: Ito
authors.forename: T
authors.initials: T
authors.lastname: Shirasaki
authors.forename: K
authors.initials: K
authors.lastname: Narita
authors.forename: K
authors.initials: K
authors.lastname: Ohnuma
authors.forename: K
authors.initials: K
authors.lastname: Kuba
authors.forename: H
authors.initials: H
authors.lastname: Kijima
mesh_terms: D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D005456:Fluorescent Dyes; D007211:Indoles; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008856:Microscopy, Fluorescence; D009046:Motor Neurons / Q000378:metabolism*; D009473:Neuronal Plasticity / Q000502:physiology; D017729:Presynaptic Terminals / Q000378:metabolism*; D011898:Ranidae; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
chemical_list: D002614:Chelating Agents; D005456:Fluorescent Dyes; D007211:Indoles; D004533:Egtazic Acid; D008274:Magnesium; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; C048960:indo-1; D002118:Calcium