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89 lines
2.0 KiB
89 lines
2.0 KiB
2 years ago
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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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