TITLE Ntype calcium channel
: used in somatic and dendritic regions
: After Borg
: Updated by Maria Markaki 03/12/03
NEURON {
SUFFIX can
USEION ca READ cai, eca WRITE ica
RANGE gcalbar, ica, po
GLOBAL hinf, minf, s_inf
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(molar) = (1/liter)
(mM) = (millimolar)
FARADAY = (faraday) (coulomb)
R = (kmole) (joule/degC)
}
PARAMETER { :parameters that can be entered when function is called in cellsetup
gcalbar = 0 (mho/cm2) : initialized conductance
ki = 0.025 (mM) :test middle point of inactivation fct
: ki = 0.01 (mM) :test middle point of inactivation fct
zetam = 3.4
zetah = 2
vhalfm =21 (mV)
vhalfh =40 (mV)
tm0=1.5(ms)
th0=75(ms)
: taumin = 10 (ms) : minimal value of the time cst
taumin = 2 (ms) : minimal value of the time cst
}
ASSIGNED { : parameters needed to solve DE
v (mV)
celsius (degC)
ica (mA/cm2)
po
cai (mM) :5e5 initial internal Ca++ concentration
eca (mV)
minf
hinf
s_inf
}
FUNCTION h2(cai(mM)) {
h2 = ki/(ki+cai)
}
STATE {
m
h
s
}
INITIAL {
rates(v,cai)
m = minf
h = hinf
s = s_inf
}
BREAKPOINT {
SOLVE states METHOD cnexp
po = m*m*h
ica = gcalbar *po*h2(cai) * (v  eca)
}
FUNCTION ghk(v(mV), ci(mM), co(mM)) (.001 coul/cm3) {
LOCAL z, eci, eco
z = (1e3)*2*FARADAY*v/(R*(celsius+273.15))
eco = co*efun(z)
eci = ci*efun(z)
:high cao charge moves inward
:negative potential charge moves inward
ghk = (.001)*2*FARADAY*(eci  eco)
}
FUNCTION efun(z) {
if (fabs(z) < 1e4) {
efun = 1  z/2
}else{
efun = z/(exp(z)  1)
}
}
DERIVATIVE states {
rates(v,cai)
m' = (minf m)/tm0
h'= (hinf  h)/th0
s' = (s_infs)/taumin
}
PROCEDURE rates(v (mV), cai(mM)) {
LOCAL a, b, alpha2
a = alpm(v)
minf = 1/(1+a)
b = alph(v)
hinf = 1/(1+b)
alpha2 = (ki/cai)^2
s_inf = alpha2 / (alpha2 + 1)
}
FUNCTION alpm(v(mV)) {
UNITSOFF
alpm = exp(1.e3*zetam*(vvhalfm)*9.648e4/(8.315*(273.16+celsius)))
UNITSON
}
FUNCTION alph(v(mV)) {
UNITSOFF
alph = exp(1.e3*zetah*(vvhalfh)*9.648e4/(8.315*(273.16+celsius)))
UNITSON
}
