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Selective disruption of
enhances or eliminates
in nerve endings
Eugene M. Silinsky*
PNAS 2008, 105-17: 6427
Martha Eugenia Ramirez-Dominguez - 092010 - MARK’S LAB JOURNAL CLUB
UCSF - SFGH
Docking: specifically attaches vesicles to the active zone;
Priming: makes the vesicles competent for Ca2+ -triggered release and
may involve a partial fusion reaction;
Fusion: final Ca2+ -regulated step that completes fusion.
Synaptic vesicle exocytosis occurs in consecutive steps:
Microdomains of high [Ca]I occur at the pore exit, because Ca2+
enter the channel faster than they can diffuse into the surrounding
Why do calcium channels (Cavs) interact
with proteins thought to be located at the
interface between a docked synaptic
vesicle and the plasma membrane?
Primed fusion-ready vesicles that are not linked to CaVs are much less likely to release their contents
when an action potential invades the nerve terminal.
It follows on from this hypothesis that regulatory processes which modulate interactions between
channels and synaptic core complexes could
play an important role in the plasticity of presynaptic events.
Molecular links between CaVs and the exocytotic machinery would guarantee that the calcium trigger initiating vesicle
fusion is located within a restricted zone where the appropriate [Ca]i is attained upon channel activation.
Synaptic vesicle fusion requires relatively high
50-100 uM [Ca]i
only attained close to the inner mouth of the activated CaVs.
SynaptotagminSynaptotagmin :: Ca2+ -binding protein, essential for Ca2+-triggered release and
probably serves as the Ca2+-sensor in fusion.
Rab3: limits the number of vesicles that can be fused as a function of Ca2+
in order to allow a temporally limited, repeatable signal.
Once membrane depolarization and Ca influx occur,
conformational changes in the SNARE complex, along with other less well defined processes,
facilitate the fusion of the two membranes and release neurotransmitter into the synapse.
Skeletal Neuromuscular Junction
G protein coupled Receptors (GPCR) :
modulated by Ca2= entrance through Cav- Channels
Interaction with Secretoty Apparatus
1) A1 – Adenosine Receptor Activation
Adenosine effect on Secretory Complex by Cavs ?
2) By BoNTx assays SNARES
important role in mediating effects of Adenosine at
mouse motor nerve
So, there is an interconection between A1R – P/Q Ca channels
mediated by SNAREs ?
The secretory apparatus and the cleavage sites for BoNtxs.
Cav channels N-type and P/Q-type contain a
Synaptic Protein Interaction (synprint) site within
the II–III loop that assembles with synaptic proteins
such as Syntaxin (Sx),
SNAP-25 (SN) and Synaptotagmin (Sg)
This association couples synaptic vesicles
and the source of extracellular calcium and
as a regulatory element
synaptic proteins may control
calcium channel function .
Isolated phrenic nerve hemidiaphragm
from Rab3A−/− mutant mice
Calcium currents were quantified by measuring voltage changes in the perineural space
The perineural recording electrodes were filled with normal physiological salt solution (3–10 MΩ)
and positioned near small axon bundles at the heminode.
The electrophysiological correlates of Ach secretion (EPPs) were also recorded to monitor
the elimination of Ach release.
The effects of Adenosine in the Rab3A-/- mutant
with and w.o. BoNTx treatment
Presynaptic ionic currents
P/Q calcium current
Cd++ & ω-agatoxin block
Important target x
to Cav inhib
Increased efficacy of adenosine in the Rab3A-/- mutant after cleavage of the
vesicle protein synaptobrevin with Botx/D.
Complete inhib of P/Q Cav
Prevent vesicle participate in
priming with t-SNARES
A model for the enhanced effects of adenosine
before and after disruption of vesicle proteins.
SV fusion is likely to be initiated by the change in conformation and/or
electrostatic potential of a Ca2+ -sensing protein.
Similarly, limiting neurotransmitter release to the particular SV that has
initiated the fusion process—out of a pool of fusion-competent vesicles—
requires a mechanism that excludes a complicated time-consuming cascade of
• what are the clostridial neurotoxins doing that
is so deadly? ‘Blocking neurotransmission’ is
the answer which prompted many physicians
‘SNARE cleavage’ is the answer that stimulated many cell biologists to use clostridial
neurotoxins as research tools for solving fundamental questions on secretion.
What will the next answer and application be?
How botulinum and tetanus neurotoxins block neurotransmitter releaseHow botulinum and tetanus neurotoxins block neurotransmitter release
Jarvis & Zamponi (2005) Cell Calcium37, 5: 483-488
Calcium in the function of the nervous system: New implications