TITLE P-type calcium channel
COMMENT
According to Benton&Raman data
lower threshold but relatively large time constant compared with Sungho's model (According to Bruce Bean)
Also the ssa is steep. In this model, it is better not to shift the SSA to the left.
time speeded up by 2 times May 9 2016 (no longer)
ENDCOMMENT
NEURON {
SUFFIX newCaP
USEION ca READ cai, cao WRITE ica
RANGE pcabar, ica,vshift,kt
GLOBAL minf, taum
GLOBAL monovalConc, monovalPerm
: THREADSAFE
}
UNITS {
(mV) = (millivolt)
(mA) = (milliamp)
(nA) = (nanoamp)
(pA) = (picoamp)
(S) = (siemens)
(nS) = (nanosiemens)
(pS) = (picosiemens)
(um) = (micron)
(molar) = (1/liter)
(mM) = (millimolar)
}
CONSTANT {
q10 = 3
F = 9.6485e4 (coulombs)
R = 8.3145 (joule/kelvin)
: cv = 19 (mV)
: ck = 5.5 (mV)
cv = 30.5 (mV)
ck = 4.113 (mV)
}
PARAMETER {
v (mV)
celsius (degC)
cai (mM)
cao (mM)
vshift =0
pcabar = 6e-5 (cm/s)
monovalConc = 140 (mM)
monovalPerm = 0
kt=1
}
ASSIGNED {
qt
ica (mA/cm2)
minf
taum (ms)
T (kelvin)
E (volt)
zeta
}
STATE { m }
INITIAL {
qt = q10^((celsius-22 (degC))/10 (degC))
T = kelvinfkt( celsius )
rates(v)
m = minf
}
BREAKPOINT {
SOLVE states METHOD cnexp
ica = (1e3) * pcabar * m * ghk(v, cai, cao, 2)
}
DERIVATIVE states {
rates(v)
m' = (minf-m)/taum
}
FUNCTION ghk( v (mV), ci (mM), co (mM), z ) (coulombs/cm3) {
E = (1e-3) * v
zeta = (z*F*E)/(R*T)
: ci = ci + (monovalPerm) * (monovalConc) :Monovalent permeability
if ( fabs(1-exp(-zeta)) < 1e-6 ) {
ghk = (1e-6) * (z*F) * (ci - co*exp(-zeta)) * (1 + zeta/2)
} else {
ghk = (1e-6) * (z*zeta*F) * (ci - co*exp(-zeta)) / (1-exp(-zeta))
}
}
PROCEDURE rates( v (mV) ) {
minf = 1 / ( 1 + exp(-(v+cv+vshift)/ck) )
taum = (1e3) * taumfkt(v)/qt/kt
}
FUNCTION taumfkt( v (mV) ) (s) {
UNITSOFF
taumfkt = (0.0002 + 0.0007031 * exp(-((v+30+vshift)/14)^2)) :Raman data
: taumfkt = (0.00002 + 0.00065 * exp(-((v+vshift)/40)^2)) :data from Biophysical Journal 108,2015: 578-584 David Naranjo
UNITSON
}
FUNCTION kelvinfkt( t (degC) ) (kelvin) {
UNITSOFF
kelvinfkt = 273.19 + t
UNITSON
}