ReDiClus Model is an acronym for Re ceptor Di ffusion & Clus ter Model.
Diffusion and Cluster Model of LTP
Diffusion and Cluster Model of LTP
Model Space
The model is simulated in a 3D space with the following parameters
There is a 3D XYZ coordinate grid
The X-Y plane has 60x60 area
The X-Y plane consists of real numbers: -30 to +30
The Z axis is only 2 levels: 0 and -1
0 represents the membrane surface
-1 represents intracellular space
Particle Types
There are 2 types of particles in the simulation 'Red' particle dots represent AMPA receptors
Red dots can randomly diffuse anywhere on the X-Y plane
Red dots only diffuse on the surface Z = 0
'Blue' particle dots represent PSD-95 molecules
Blue dots are contained in predefined PSD areas and cannot leave
Blue dots can exist at the surface Z = 0 or intracellularly Z = -1
two independent processes
In this model, there are two independently occurring processes. 1. Blue dots can be expressed at the surface or internalized within their PSD area
The Blue dot internalization/externalization rate properties are set by the Shouval cluster model equations.
2. Red dots diffuse on the X-Y plane with brownian motion
Each Red dot has an initial step size randomly drawn from a normal distribution with a mean = 1 and sd = .2
The step size for Red dots is dynamically altered when it's located in a PSD area In a PSD, the step size is reduced by a by some factor based on the number of Blue dots currently expressed at the surface of that PSD
The more Blue dots at the surface, the more the step size is reduced
The current step size function is:
f (Rstep ) = R * (10*(1 ⁄ Bn ))
where Rstep is the baseline Red dot step size
where Bn is number of Blue dots currently expressed at the PSD surface Several screen shots of the dynamic graphs in the model
FIG: {{{2}}} CLICK AWAY FROM IMAGE TO CLOSE }}FIG: {{{2}}} CLICK AWAY FROM IMAGE TO CLOSE }}
Error creating thumbnail: File missing • Diffusion rate was measured as µm2 /s Choquet et al (2010) CaMKII triggers the diffusional trapping of surface AMPARs through phosphorylation of stargazin. Neuron
Choquet 2007 Real Time Receptor Diffusion
Choquet 2007 Real Time Receptor Diffusion Analysis
The video represents a 10µm × 10µm section scaled to a 535px × 535px video.
The analysis below documents one instance of Qdot diffusion, between the 6s-7s time points.
This instance was chosen because of the clarity of motion and no Qdot flicker.
The Qdot (center) moves from pixel location (X:291, Y:302) at 6.78s to (X:319, Y346) at 6.98s
That is a distance of 52.2px in 200ms
Qdot velocity: Qv µm ms
Note this diffusion rate of 5µm/s is 10-fold higher than the median diffusion rate reported above.
An upper bound of 5µm/s means that receptors can move between synapses in fractions of a second. Figures:
FIG: {{{2}}} CLICK AWAY FROM IMAGE TO CLOSE }}FIG: {{{2}}} CLICK AWAY FROM IMAGE TO CLOSE }}FIG: {{{2}}} CLICK AWAY FROM IMAGE TO CLOSE }}FIG: {{{2}}} CLICK AWAY FROM IMAGE TO CLOSE }}
Receptor Diffusion Rate Best Estimates
GABAA: .01 - .05 µm2 /s FIG: Choquet 2010
