Scuola di Neuroscienze Università degli Studi di Torino Corso di Dottorato Torino, 7 Settembre 2006 Canali del calcio presinaptici: distribuzione e neurotrasmissione
Presynaptic Ca 2+ channels: types and distribution
The synaptic transmission
The classical approach to identify the contribution of presynaptic Ca 2+ channels in central synapses
Action potential-evoked GABAergic IPSCs ldelli et al. (2002) Europ J Neurosci 16: 2297 pre post Monosynaptic preparation
Mintz et al., 1995 Neuron 15: 675 presynaptic stimuli postsynaptic recording presynaptic Ca 2+ -entry (fluorescence) Ca 2+ entry at cerebellar excitatory synapses is controlled by N, P/Q and R-type channels
. while neurotransmitter release is controlled only by N and P/Q-type channels
GABA release is controlled by N- and P/Q-type Ca channels in interneurons of hippocampal slices Wilson et al., 2001 Neuron 31: 453 N-type channels P/Q-type channels N and P/Q-type channels
From these experiments we can conclude that: Ca 2+ enters through various voltage-gated Ca 2+ channels (N, P/Q, R.. L, T) Secretion is strictly associated to N and P/Q-type channels, which are possibly co-localized to the release sites There are release sites controlled by P/Q, others controlled by N and a group controlled by N and P/Q
Supra-additivity supports a model of synaptic terminals with a nonuniform distribution of Ca 2+ channels
A direct approach to study presynaptic Ca 2+ channels and neurosecretion: the giant synapse of the calyx of Held
The calyx of Held allows to record directly presynaptic and postsynaptic currents presynaptic calyx Glutamatergic giant synapse principal neuron in the MNTB nucleus 0.3 mm pre MNTB (Medial Nucleus of the Trapezoid Body) in the brainstem of the acustic pathway post
P-type channels control fully the EPSCs but partially presynaptic [Ca 2+ ] aga aga N-type channels control partially the EPSCs and presynaptic [Ca 2+ ] GVIA GVIA
P-type channels have a steeper Ca 2+ -dependence than N-type channels P-type N-type Release [Ca terminal ] m Wu et al., 1999 J Neurosci, 19: 726
P/Q-type and N-type channels co-localize with synaptotagmin Ca 2+ channels synaptotagmin merge P/Q-type (a1 A ) N-type (a1 B ) R-type (a1 E )
Why N and P/Q channels are co-localized at the release sites?
Exist a strict interaction between Ca 2+ channels (P/Q and N), membrane-binding and vesicle-binding proteins Catteral, 2000 Annu Rev Cell Dev Bio. 16: 521
Co-localization of N and P/Q type channels at the release sites is favoured by the interaction of a channel region (synprint) with syntaxin and other vesicle binding proteins from Purves et al., 2004 Neuroscience, Sinauer Associated Inc.
The synprint region
Are N and P/Q-type channels the only voltagegated Ca 2+ channels controlling neurotransmitter release?
In isolated hippocampal neurones, focal stimulation is controlled by L-type channels IPSCs In slices, presynaptic response is controlled by N and P/Q-type channels IPSCs
. a possible explanation
In isolated hippocampal neurons the post-tetanic potentiation (PTP) is controlled by L-type channels IPSCs (before PTP, at normal stimulation, 0.2 Hz) IPSCs (after PTP, at normal stimulation, 0.2 Hz)
R- and L-type Ca 2+ channels contribute to secretion during prolonged presynaptic stimuli
Action potential-evoked GABAergic IPSCs pre post Monosynaptic preparation ldelli et al. (2002) Europ J Neurosci 16: 2297
Contribution of N and P/Q-type channels to AP-evoked IPSCs in cultured hippocampal neurons Baldelli et al. (2005) J Neurosci 25: 3358
KCl-evoked IPSCs induce long lasting eipscs with comparable amplitudes and pharmacology Baldelli et al. (2002) Europ J Neurosci 16: 2297
Contribution of R-type channels is enhanced during KCl-evoked IPSCs ldelli et al. (2002) Europ J Neurosci 16: 2297 Baldelli et al. (2005) J Neurosci 25: 3358
Conclusions
Vesicle docking, priming, depletion and replenishment are all Ca 2+ -dependent processes L L L R R N N P/Q P/Q N.. are they controlled by the same Ca channel types?
Dip. Neuroscienze, Torino Valentina Carabelli Andrea Marcantoni Valentina Comunanza Daniela Guido Pietro Baldelli (Dip. Biomedicina Sperimentale, Genova) Monica Novara (Novartis, Milano) Tiziana Cesetti (DeptNeuroscience, Heidelberg) Jesus-Miguel Hernandez-Guijo (Dep. Farmacologia, UAM, Madrid) Anna Giancippoli (Novartis, Milano) Paolo Cesare (E.B.R.I., Roma) Valeria Magnelli (Dip. Scienze e Tecnologie Avanzate, Alessandria) Michele Lovallo (C.N.R., Università di Potenza) Daniela Platano (Dip. Fisiologia Umana e Generale, Bologna) Emanuele Sher (Ely Lilly Res. Center, Surrey, UK) Giorgio Aicardi (Dip. Fisiologia Umana e Generale, Bologna) Claudio Grassi (Dip. Fisiologia Umana, Univ. Cattolica del Sacro Cuore, Roma) Marcello D Ascenzo Antonio Garcia (Dep. Farmacologia, UAM, Madrid) Almudena Albillos Luis Gandia Carmen Montiel Antonio Artalejo (Dep. Toxicologia y Farmacologia, Univ Complutense, Madrid) Helmut Zucker (M.P.I. fur Neurobiologie, Martinsried, Germany) Dieter Swandulla ( Dept. Neuropharmacology, Bonn, Germany)