ABSTRACT:
Edelstein1996 - EPSP ACh event
Model of a nicotinic Excitatory Post-Synaptic Potential in a
Torpedo electric organ. Acetylcholine is not represented
explicitely, but by an event that changes the constants of
transition from unliganded to liganded.
This model has initially been encoded using StochSim.
This model is described in the article:
A kinetic mechanism for
nicotinic acetylcholine receptors based on multiple allosteric
transitions.
Edelstein SJ, Schaad O, Henry E,
Bertrand D, Changeux JP.
Biol Cybern 1996 Nov; 75(5):
361-379
Abstract:
Nicotinic acetylcholine receptors are transmembrane
oligomeric proteins that mediate interconversions between open
and closed channel states under the control of
neurotransmitters. Fast in vitro chemical kinetics and in vivo
electrophysiological recordings are consistent with the
following multi-step scheme. Upon binding of agonists, receptor
molecules in the closed but activatable resting state (the
Basal state, B) undergo rapid transitions to states of higher
affinities with either open channels (the Active state, A) or
closed channels (the initial Inactivatable and fully
Desensitized states, I and D). In order to represent the
functional properties of such receptors, we have developed a
kinetic model that links conformational interconversion rates
to agonist binding and extends the general principles of the
Monod-Wyman-Changeux model of allosteric transitions. The
crucial assumption is that the linkage is controlled by the
position of the interconversion transition states on a
hypothetical linear reaction coordinate. Application of the
model to the peripheral nicotine acetylcholine receptor (nAChR)
accounts for the main properties of ligand-gating, including
single-channel events, and several new relationships are
predicted. Kinetic simulations reveal errors inherent in using
the dose-response analysis, but justify its application under
defined conditions. The model predicts that (in order to
overcome the intrinsic stability of the B state and to produce
the appropriate cooperativity) channel activation is driven by
an A state with a Kd in the 50 nM range, hence some 140-fold
stronger than the apparent affinity of the open state deduced
previously. According to the model, recovery from the
desensitized states may occur via rapid transit through the A
state with minimal channel opening, thus without necessarily
undergoing a distinct recovery pathway, as assumed in the
standard 'cycle' model. Transitions to the desensitized states
by low concentration 'pre-pulses' are predicted to occur
without significant channel opening, but equilibrium values of
IC50 can be obtained only with long pre-pulse times.
Predictions are also made concerning allosteric effectors and
their possible role in coincidence detection. In terms of
future developments, the analysis presented here provides a
physical basis for constructing more biologically realistic
models of synaptic modulation that may be applied to artificial
neural networks.
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Nicolas Le Novère 
