TITLE: mfbhh.mod Sodium and potassium channels of mossy fiber boutons
COMMENT
This is the HodgkinHuxley treatment for the set of sodium, potassium,
and leakage channels found in the hippocampal mossy fiber boutons.
("Presynaptic action potential amplification by voltagegated Na+ channels in
hippocampal mossy fiber boutons" Neuron 45:405417 (2005).)
Global activation & inactivation shift; make vShift (Donnan) global by 12 mV.
"Engel & Jonas model (2005)" reconstructed by Kamiya
ENDCOMMENT
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(S) = (siemens)
}
? interface
NEURON {
SUFFIX mfbhh
USEION na READ ena WRITE ina
USEION k READ ek WRITE ik
NONSPECIFIC_CURRENT il
RANGE gnabar, gkbar, gl, el, gna, gk
GLOBAL minf, hinf, ninf, rinf, mtau, htau, ntau, rtau
THREADSAFE : assigned GLOBALs will be per thread
}
PARAMETER {
gnabar = 0.05 (S/cm2)
gkbar = 0.036 (S/cm2)
gl = .0001 (S/cm2)
el = 81 (mV)
}
STATE {
m h n r
}
ASSIGNED {
v (mV)
celsius (degC)
ena (mV)
ek (mV)
gna (S/cm2)
gk (S/cm2)
ina (mA/cm2)
ik (mA/cm2)
il (mA/cm2)
minf hinf ninf rinf
mtau (ms) htau (ms) ntau (ms) rtau (ms)
}
? currents
BREAKPOINT {
SOLVE states METHOD cnexp
gna = gnabar*m*m*m*h
ina = gna*(v  ena)
gk = gkbar*n*n*n*n*r
ik = gk*(v  ek)
il = gl*(v  el)
}
INITIAL {
rates(v)
m = minf
h = hinf
n = ninf
r = rinf
}
? states
DERIVATIVE states {
rates(v)
m' = (minfm)/mtau
h' = (hinfh)/htau
n' = (ninfn)/ntau
r' = (rinfr)/rtau
}
:LOCAL q10
? rates
PROCEDURE rates(v(mV)) { :Computes rate and other constants at current v.
:Call once from HOC to initialize inf at resting v.
LOCAL alpha, beta, sum, q10
TABLE minf, mtau, hinf, htau, ninf, ntau, rinf, rtau DEPEND celsius FROM 100 TO 100 WITH 200
UNITSOFF
q10 = 3^((celsius  23)/10)
:"m" sodium activation system
alpha = 93.8285*vtrap((v12105.023),17.7094)
beta = 0.168396*exp((v12)/23.2707)
sum = alpha + beta
mtau = 1/(q10*sum)
minf = alpha/sum
:"h" sodium inactivation system
alpha = 0.000354*exp((v12)/18.706)
beta = 6.62694/(exp((v12+17.6769)/13.3097)+1)
sum = alpha + beta
htau = 1/(q10*sum)
hinf = alpha/sum
:"n" potassium activation system
alpha = .01*vtrap((v+55),10)
beta = .125*exp((v+65)/80)
sum = alpha + beta
ntau = 1/(q10*sum)
ninf = alpha/sum
:"r" potassium inactivation system
alpha = 0.0000256077*exp(v/45.4217)
beta = 0.0330402/(exp((v+45.6599)/2.30235)+1) :Recombinant Kv1.4
sum = alpha + beta
rtau = 1/(q10*sum)
rinf = alpha/sum
}
FUNCTION vtrap(x,y) { :Traps for 0 in denominator of rate eqns.
if (fabs(x/y) < 1e6) {
vtrap = y*(1  x/y/2)
}else{
vtrap = x/(exp(x/y)  1)
}
}
UNITSON
