TITLE Voltage-gated potassium channel from Kv4 subunits
COMMENT
Gabriela Cirtala, May 15, 2024
Our modelling approach of Kv4 follows the experimental data in (Sacco et al, 2002, Journal of Physiology)
and (Gunay et al, 2008, The Journal of Neuroscience). Both these works show a fast and slow component of Kv4,
which in these mod files we refer to as Kv4f and Kv4s.
Kv4 total = Kv4f + Kv4s
NEURON implementation of a potassium channel from Kv4 subunits
Kv4 activation from Sacco inactivation from SD
Yunliang Zang April 16th 2015
ENDCOMMENT
NEURON {
SUFFIX Kv4s
USEION k READ ek WRITE ik
RANGE gk, gbar, ik,vshift
: GLOBAL ninf, taun, hinf, tauh
: THREADSAFE
}
UNITS {
(mV) = (millivolt)
(mA) = (milliamp)
(nA) = (nanoamp)
(pA) = (picoamp)
(S) = (siemens)
(nS) = (nanosiemens)
(pS) = (picosiemens)
(um) = (micron)
(molar) = (1/liter)
(mM) = (millimolar)
}
CONSTANT {
q10 = 3
F = 9.6485e4 (coulombs)
R = 8.3145 (joule/kelvin)
can = 0.15743 (1/ms)
cvan = 57 (mV)
ckan = -32.19976 (mV)
cbn = 0.15743 (1/ms)
cvbn = 57 (mV)
ckbn = 37.51346 (mV)
cah = 0.01342 (1/ms)
cvah = 60 (mV)
ckah = -7.86476 (mV)
cbh = 0.04477 (1/ms)
cvbh = 54 (mV)
ckbh = 11.3615 (mV)
vh = -75.30348 (mV)
kh = -6.06329 (mV)
ki = 150 (mM) :from Stephane
ko = 2.5 (mM)
}
PARAMETER {
v (mV)
celsius (degC)
vshift = 0
gbar = 0.0039 (mho/cm2) <0,1e9>
}
ASSIGNED {
ik (mA/cm2)
ek (mV)
gk (mho/cm2)
g (coulombs/cm3)
T (kelvin)
qt
E (volt)
zeta
ninf
taun (ms)
alphan (1/ms)
betan (1/ms)
alphah (1/ms)
betah (1/ms)
hinf
: h1inf
: h2inf
tauh (ms)
: tauh2 (ms)
}
STATE { n h }
INITIAL {
T = kelvinfkt (celsius)
qt = q10^((celsius-23 (degC))/10 (degC))
rates(v)
n = ninf
h = hinf
}
BREAKPOINT {
SOLVE states METHOD cnexp
gk = gbar * n*n*n*n*h
ik = gk * (v - ek)
}
DERIVATIVE states {
rates(v)
n' = (ninf-n)/taun
h' = (hinf-h)/tauh
}
PROCEDURE rates(v (mV)) {
alphan = alphanfkt(v)
betan = betanfkt(v)
: ninf = alphan / (alphan+betan)
: ninf = (1/(1+exp(-(v+27)/8.8)))^(1/4)
ninf = 1.0 / (1.0 + exp((-49 - v)/12.5))
taun = 1/((alphan+betan)*qt)
alphah = alphahfkt(v)
betah = betahfkt(v)
: h1inf = alphah / (alphah + betah)
: h2inf = alphah / (alphah + betah)
hinf = 1/(1+exp((v-(vh-vshift))/-kh))
: h2inf =1/(1+exp((v-(vh-vshift))/-kh))
: tauh1 = (1.96+2*1.59/(exp((-92-v)/13.8)+exp((v+92)/13.8)))/qt
tauh =100/qt
g = ghk(v, ki, ko, 1)
}
FUNCTION ghk( v (mV), ki (mM), ko (mM), z ) (coulombs/cm3) {
E = (1e-3) * v
zeta = (z*F*E)/(R*T)
if ( fabs(1-exp(-zeta)) < 1e-6 ) {
ghk = (1e-6) * (z*F) * (ki - ko*exp(-zeta)) * (1 + zeta/2)
} else {
ghk = (1e-6) * (z*zeta*F) * (ki - ko*exp(-zeta)) / (1-exp(-zeta))
}
}
FUNCTION alphanfkt(v (mV)) (1/ms) {
alphanfkt = can * exp(-(v+cvan)/ckan)
}
FUNCTION betanfkt(v (mV)) (1/ms) {
betanfkt = cbn * exp(-(v+cvbn)/ckbn)
}
FUNCTION kelvinfkt( t (degC) ) (kelvin) {
kelvinfkt = 273.19 + t
}
FUNCTION alphahfkt(v (mV)) (1/ms) {
alphahfkt = cah / (1+exp(-(v+cvah)/ckah))
}
FUNCTION betahfkt(v (mV)) (1/ms) {
betahfkt = cbh / (1+exp(-(v+cvbh)/ckbh))
}