TITLE na3
: Na current
: modified from Jeff Magee. M.Migliore may97
: added sh to account for higher threshold M.Migliore, Apr.2002
NEURON {
SUFFIX na3
USEION na READ ena WRITE ina
RANGE gbar, ar, sh
GLOBAL minf, hinf, mtau, htau, sinf, taus,qinf, thinf
}
PARAMETER {
sh = 8 (mV)
gbar = 0.032 (mho/cm2)
tha = 30 (mV) : v 1/2 for act
qa = 7.2 (mV) : act slope (4.5)
Ra = 0.4 (/ms) : open (v)
Rb = 0.124 (/ms) : close (v)
thi1 = 45 (mV) : v 1/2 for inact
thi2 = 45 (mV) : v 1/2 for inact
qd = 1.5 (mV) : inact tau slope
qg = 1.5 (mV)
mmin=0.02
hmin=0.5
q10=2
Rg = 0.01 (/ms) : inact recov (v)
Rd = .03 (/ms) : inact (v)
qq = 10 (mV)
tq = 55 (mV)
thinf = 50 (mV) : inact inf slope
qinf = 4 (mV) : inact inf slope
vhalfs=60 (mV) : slow inact.
a0s=0.0003 (ms) : a0s=b0s
zetas=12 (1)
gms=0.2 (1)
smax=10 (ms)
vvh=58 (mV)
vvs=2 (mV)
ar=0.5 (1) : 1=no inact., 0=max inact.
ena = 55 (mV) : must be explicitly def. in hoc
celsius
v (mV)
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(pS) = (picosiemens)
(um) = (micron)
}
ASSIGNED {
ina (mA/cm2)
thegna (mho/cm2)
minf hinf
mtau (ms) htau (ms)
sinf (ms) taus (ms)
}
STATE { m h s}
BREAKPOINT {
SOLVE states METHOD cnexp
thegna = gbar*m*m*m*h*s
ina = thegna * (v  ena)
}
INITIAL {
trates(v,ar,sh)
m=minf
h=hinf
s=sinf
}
FUNCTION alpv(v(mV)) {
alpv = 1/(1+exp((vvvhsh)/vvs))
}
FUNCTION alps(v(mV)) {
alps = exp(1.e3*zetas*(vvhalfssh)*9.648e4/(8.315*(273.16+celsius)))
}
FUNCTION bets(v(mV)) {
bets = exp(1.e3*zetas*gms*(vvhalfssh)*9.648e4/(8.315*(273.16+celsius)))
}
LOCAL mexp, hexp, sexp
DERIVATIVE states {
trates(v,ar,sh)
m' = (minfm)/mtau
h' = (hinfh)/htau
s' = (sinf  s)/taus
}
PROCEDURE trates(vm,a2,sh2) {
LOCAL a, b, c, qt
qt=q10^((celsius24)/10)
a = trap0(vm,tha+sh2,Ra,qa)
b = trap0(vm,thash2,Rb,qa)
mtau = 1/(a+b)/qt
if (mtau<mmin) {mtau=mmin}
minf = a/(a+b)
a = trap0(vm,thi1+sh2,Rd,qd)
b = trap0(vm,thi2sh2,Rg,qg)
htau = 1/(a+b)/qt
if (htau<hmin) {htau=hmin}
hinf = 1/(1+exp((vmthinfsh2)/qinf))
c=alpv(vm)
sinf = c+a2*(1c)
taus = bets(vm)/(a0s*(1+alps(vm)))
if (taus<smax) {taus=smax}
}
FUNCTION trap0(v,th,a,q) {
if (fabs(vth) > 1e6) {
trap0 = a * (v  th) / (1  exp((v  th)/q))
} else {
trap0 = a * q
}
}
