Scuola di NeuroscienzeUniversità degli Studi di Torino

Corso di DottoratoTorino, 7 Settembre 2006

Canali del calcio presinaptici: distribuzione e neurotrasmissione

CNR-INFM

Presynaptic Ca2+ channels:types and distribution

from Purves et al., 2004 Neuroscience, Sinauer Associated Inc., 3rd edition

The synaptic transmission

The classical approach to identify the contribution of presynaptic Ca2+ channels

in central synapses

Baldelli et al. (2002) Europ J Neurosci 16: 2297

prepost

Action potential-evoked GABAergic IPSCs

Monosynaptic preparation

Ca2+ entry at cerebellar excitatory synapses is

controlled by N, P/Q and R-type channels

Mintz et al., 1995 Neuron 15: 675

presynaptic Ca2+-entry(fluorescence)

presynaptic stimuli

postsynapticrecording

Mintz et al., 1995 Neuron 15: 675

…. 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

N-type channels

P/Q-type channels

N and P/Q-type channels

Wilson et al., 2001 Neuron 31: 453

From these experiments we can conclude that:

• Ca2+ enters through various voltage-gated Ca2+ 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

Reid et al., 2003 TINS 26: 683

“Supra-additivity” supports a model of synaptic terminals with a non-uniform distribution of Ca2+

channels

A direct approach to study presynaptic Ca2+ channels and neurosecretion:

the giant synapse of the calyx of Held

The calyx of Held allows to record directly presynaptic and postsynaptic currents

principal neuron in the MNTB

presynapticcalyx

0.3 µmnucleus

Saetzler et al., 2002 J. Neurosci., 22: 10567

pre

post

MNTB (Medial Nucleus of the Trapezoid Body) in the brainstem of the acustic pathway

Glutamatergic giant synapse

aga aga

P-type channels control fully the EPSCs but partially presynaptic [Ca2+]

GVIA

GVIA

N-type channels control partially the EPSCs and presynaptic [Ca2+]

Wu et al., 1999 J Neurosci, 19: 726

P-type channels have a steeper Ca2+-dependence than N-type channels

P-type N-type

Wu et al., 1999 J Neurosci, 19: 726

Release [Caterminal]m

P/Q-type and N-type channels co-localize with synaptotagmin

synaptotagminCa2+ channels merge

P/Q-type (α1A)

N-type (α1B)

R-type (α1E)

Wu et al., 1999 J Neurosci, 19: 726

Why N and P/Q channels are co-localized at the release sites?

Catteral, 2000 Annu Rev Cell Dev Bio. 16: 521

Exist a strict interaction between Ca2+ channels (P/Q and N), membrane-binding and vesicle-binding proteins

from Purves et al., 2004 Neuroscience, Sinauer Associated Inc.

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

Spafford & Zamponi, 2003 Curr Op Neurobiol 13: 308

The “synprint region”

Are N and P/Q-type channels the only voltage-gated Ca2+ channels controlling

neurotransmitter release?

Murakami et al., 2002 Brain Research, 951: 121

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

Murakami et al., 2002 Brain Research, 951: 121

Jensen et al., 1999 J. Neurophysiol 81: 1225

In isolated hippocampal neurons the post-tetanic potentiation (PTP) iscontrolled 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 Ca2+ channels contribute to secretion during prolonged presynaptic stimuli

Baldelli et al. (2002) Europ J Neurosci 16: 2297

prepost

Action potential-evoked GABAergic IPSCs

Monosynaptic preparation

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

Baldelli et al. (2005) J Neurosci 25: 3358Baldelli et al. (2002) Europ J Neurosci 16: 2297

Conclusions

Vesicle docking, priming, depletion and replenishment are all Ca2+-dependent processes

P/Q P/QNN

N

…….. are they controlled by the same Ca channel types?

R

LL

L

R

Dip. Neuroscienze, TorinoValentina Carabelli Andrea MarcantoniValentina ComunanzaDaniela Guido

Pietro Baldelli (Dip. Biomedicina Sperimentale, Genova)Monica Novara (Novartis, Milano)Tiziana Cesetti (Dept Neuroscience, 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 AlbillosLuis GandiaCarmen 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)