COMMENT
na.mod
Sodium channel, Hodgkin-Huxley style kinetics.
Kinetics were fit to data from Huguenard et al. (1988) and Hamill et
al. (1991)
qi is not well constrained by the data, since there are no points
between -80 and -55. So this was fixed at 5 while the thi1,thi2,Rg,Rd
were optimized using a simplex least square proc
voltage dependencies are shifted approximately from the best
fit to give higher threshold
Author: Zach Mainen, Salk Institute, 1994, zach@salk.edu
ENDCOMMENT
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
NEURON {
SUFFIX na
USEION na READ ena WRITE ina
RANGE m, h, gna, gbar
GLOBAL tha, thi1, thi2, qa, qi, qinf, thinf
RANGE minf, hinf, mtau, htau
GLOBAL Ra, Rb, Rd, Rg
GLOBAL q10, temp, tadj, vmin, vmax, vshift
}
PARAMETER {
gbar = 1000 (pS/um2) : 0.12 mho/cm2
vshift = -10 (mV) : voltage shift (affects all)
tha = -35 (mV) : v 1/2 for act (-42)
qa = 9 (mV) : act slope
Ra = 0.182 (/ms) : open (v)
Rb = 0.124 (/ms) : close (v)
thi1 = -50 (mV) : v 1/2 for inact
thi2 = -75 (mV) : v 1/2 for inact
qi = 5 (mV) : inact tau slope
thinf = -65 (mV) : inact inf slope
qinf = 6.2 (mV) : inact inf slope
Rg = 0.0091 (/ms) : inact (v)
Rd = 0.024 (/ms) : inact recov (v)
temp = 23 (degC) : original temp
q10 = 2.3 : temperature sensitivity
v (mV)
dt (ms)
celsius (degC)
vmin = -120 (mV)
vmax = 100 (mV)
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(pS) = (picosiemens)
(um) = (micron)
}
ASSIGNED {
ina (mA/cm2)
gna (pS/um2)
ena (mV)
minf hinf
mtau (ms) htau (ms)
tadj
}
STATE { m h }
INITIAL {
trates(v+vshift)
m = minf
h = hinf
}
BREAKPOINT {
SOLVE states
gna = tadj*gbar*m*m*m*h
ina = (1e-4) * gna * (v - ena)
}
LOCAL mexp, hexp
PROCEDURE states() { :Computes state variables m, h, and n
trates(v+vshift) : at the current v and dt.
m = m + mexp*(minf-m)
h = h + hexp*(hinf-h)
VERBATIM
return 0;
ENDVERBATIM
}
PROCEDURE trates(v) {
LOCAL tinc
TABLE minf, mexp, hinf, hexp
DEPEND dt, celsius, temp, Ra, Rb, Rd, Rg, tha, thi1, thi2, qa, qi, qinf
FROM vmin TO vmax WITH 199
rates(v): not consistently executed from here if usetable == 1
tadj = q10^((celsius - temp)/10)
tinc = -dt * tadj
mexp = 1 - exp(tinc/mtau)
hexp = 1 - exp(tinc/htau)
}
PROCEDURE rates(vm) {
LOCAL a, b
a = trap0(vm,tha,Ra,qa)
b = trap0(-vm,-tha,Rb,qa)
mtau = 1/(a+b)
minf = a*mtau
:"h" inactivation
a = trap0(vm,thi1,Rd,qi)
b = trap0(-vm,-thi2,Rg,qi)
htau = 1/(a+b)
hinf = 1/(1+exp((vm-thinf)/qinf))
}
FUNCTION trap0(v,th,a,q) {
if (fabs(v/th) > 1e-6) {
trap0 = a * (v - th) / (1 - exp(-(v - th)/q))
} else {
trap0 = a * q
}
}