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88 lines
2.0 KiB
88 lines
2.0 KiB
COMMENT |
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cleftXmtr |
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This is simple state model that generates "cleft" transmitter, through |
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the following scheme: |
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A netreceive block receives the driving event. This forces XV (the vesicle |
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state) to be set to XMax to mimic the release of a vesicle. |
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Then: |
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XV --> XC --> XU |
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where XV is the vesicle transmitter, XC is the cleft transmitter and |
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XU is transmitter that has been taken up. The forward rates are finite, and the |
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reverse rates are 0 (XU is an absorbing state) |
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The forward rate kv1 mimics simple first-order diffusion across the cleft |
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The forward rate ku1 mimics simple first-order uptake from the cleft |
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The concentration XC is available to the program as Xmtr. |
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XMax is the max cleft concentration of transmitter. |
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Because vesicle release events at a single presynaptic terminal can be nearly |
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simultaneous, it is important that this mechanism does not have a refractory |
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period. We also assume that the uptake mechanism is not saturable. |
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Paul B. Manis, Ph.D. |
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UNC Chapel Hill |
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3 Jan 2010 |
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ENDCOMMENT |
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INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)} |
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DEFINE NSTEP 5 |
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NEURON { |
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POINT_PROCESS cleftXmtr |
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POINTER pre |
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RANGE KV, KU, XMax |
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RANGE CXmtr, preThresh |
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} |
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UNITS { |
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(nA) = (nanoamp) |
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} |
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PARAMETER { : Parameters are chosen from best fit to stellate cell data in VCN |
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KV = 531 (/ms) <0,1e9> : release rate from vesicle |
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KU = 4.17 (/ms) <0,1e3> : uptake rate |
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XMax = 0.731 (mM) |
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preThresh = 0 |
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} |
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ASSIGNED { |
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pre |
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CXmtr (mM) |
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preLast (1) |
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tLast |
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} |
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STATE { |
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XV : Vesicle transmitter (just released) |
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XC : Cleft transmitter (e.g., at receptor) |
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XU : Uptake state (dead state... ) |
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} |
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INITIAL { |
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XV = 0 |
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XC = 0 (mM) |
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XU = 0 |
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CXmtr = 0.0 |
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preLast = 0.0 |
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tLast = 0.0 |
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} |
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BREAKPOINT { |
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SOLVE kstates METHOD sparse |
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CXmtr = XC*XMax |
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} |
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KINETIC kstates { |
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~ XV <-> XC (KV, 0.0) |
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~ XC <-> XU (KU, 0.0) |
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: note that this mechanism has no CONSERVATION : XU can accumulate as much |
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: as needed. |
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} |
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NET_RECEIVE(conc (mM)) { : detect and cause a release event |
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XV = XV + 1 |
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}
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