NEURON {
SUFFIX cap_gp
USEION ca READ cai, cao WRITE ica
RANGE gbar, ica
GLOBAL minf,mtau
GLOBAL monovalConc, monovalPerm
}
UNITS {
(mV) = (millivolt)
(mA) = (milliamp)
(mM) = (milli/liter)
(S) = (siemens)
F = 9.6485e4 (coul)
R = 8.3145 (joule/degC)
(mC) = (millicoul)
}
PARAMETER {
v (mV)
gbar = 1 (cm/s)
monovalConc = 140 (mM)
monovalPerm = 0
cai (mM)
cao (mM)
celsius (degC)
}
ASSIGNED {
ica (mA/cm2)
minf
mtau (ms)
T (degC)
E (volts)
g (cm/s)
}
STATE {
m
}
INITIAL {
rates(v)
m = minf
}
BREAKPOINT {
SOLVE states METHOD cnexp
g = gbar * m
ica = g * ghk(v, cai, cao, 2)
}
DERIVATIVE states {
rates(v)
m' = (minf - m)/mtau
}
FUNCTION ghk( v(mV), ci(mM), co(mM), z) (mC/cm3) { LOCAL Ci
T = 22 + 273.19 : Kelvin
E = v * 1e-3 (volts/mV)
Ci = ci + (monovalPerm) * (monovalConc) : Monovalent permeability
if (fabs(1-exp(-z*(F*E)/(R*T))) < 1e-6) { : denominator is small -> Taylor series
ghk = (1e-3) * z * F * (Ci-co*exp(-z*(F*E)/(R*T)))*(1-(z*(F*E)/(R*T)))
} else {
ghk = (1e-3) * z^2*(E*F^2)/(R*T)*(Ci-co*exp(-z*(F*E)/(R*T)))/(1-exp(-z*(F*E)/(R*T)))
}
}
PROCEDURE rates (v (mV)) {
LOCAL q10
minf = 1/(1+exp(-(v + 19 (mV) ) / 5.5 (mV)))
q10 = 3^((celsius - 22 (degC))/10 (degC) )
mtau = q10*(mtau_func(v)) * 1e3
}
FUNCTION mtau_func( v (mV) ) (ms) {
if (v > -50) {
mtau_func = .000191 (ms) + .00376 (ms) *exp(-((v+41.9 (mV))/27.8 (mV) )^2)
} else {
mtau_func = .00026367 (ms) + .1278 (ms) * exp(v* .10327 (1/mV))
}
}