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capump.mod
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capump.mod
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TITLE decay of submembrane calcium concentration
:
: Internal calcium concentration due to calcium currents and pump.
: Pump action is approximated by a simple first order decay.
NEURON {
SUFFIX cad
USEION ca READ ica, cai WRITE cai
RANGE depth,kd,cainf,taur
}
UNITS {
(molar) = (1/liter) : moles do not appear in units
(mM) = (millimolar)
(um) = (micron)
(mA) = (milliamp)
(msM) = (ms mM)
}
CONSTANT {
FARADAY = 96489 (coul) : moles do not appear in units
}
PARAMETER {
depth = .1 (um) : depth of shell
taur = 1.5 (ms) : remove first-order decay
cainf = 0.0001 (mM)
kd = 0.0001 (mM)
}
STATE {
cai (mM)
}
INITIAL {
cai = kd
}
ASSIGNED {
ica (mA/cm2)
drive_channel (mM/ms)
}
BREAKPOINT {
SOLVE state METHOD derivimplicit
}
DERIVATIVE state {
drive_channel = - (10000) * ica / (2 * FARADAY * depth)
if (drive_channel <= 0.) { drive_channel = 0. } : cannot pump below resting level
cai' = drive_channel + (cainf-cai)/taur
}