TITLE K-A channel from Klee Ficker and Heinemann
: modified by Brannon and Yiota Poirazi (poirazi@LNC.usc.edu)
: to account for Hoffman et al 1997 proximal region kinetics
: used only in soma and sections located < 100 microns from the soma
NEURON {
SUFFIX kap
USEION k READ ko, ki WRITE ik :Changed from READ ek, 23/04/2010,Nassi
RANGE gkabar, ik
GLOBAL ninf,linf,taul,taun,lmin
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
}
PARAMETER { :parameters that can be entered when function is called in cell-setup
gkabar = 0 (mho/cm2) :initialized conductance
vhalfn = 11 (mV) :activation half-potential
vhalfl = -56 (mV) :inactivation half-potential
:vhalfl = -56 (mV) :inactivation half-potential
a0n = 0.05 (/ms) :parameters used
zetan = -1.5 (1) :in calculation of (-1.5)
zetal = 3 (1) :steady state values(3)
gmn = 0.55 (1) :and time constants(0.55) change to get an effect on spike repolarization
gml = 1 (1)
:gml = 1 (1)
lmin = 2 (ms)
nmin = 0.1 (ms)
pw = -1 (1)
tq = -40 (mV)
qq = 5 (mV)
q10 = 5 :temperature sensitivity
}
ASSIGNED { :parameters needed to solve DE
v (mV)
ek (mV) :K reversal potential (reset in cell-setup.hoc)
celsius (degC)
ik (mA/cm2)
ninf
linf
taul (ms)
taun (ms)
ko (mM)
ki (mM)
}
STATE { :the unknown parameters to be solved in the DEs
n l
}
LOCAL qt
INITIAL { :initialize the following parameter using rates()
qt = q10^((celsius-24)/10(degC)) : temprature adjustment factor
rates(v)
n = ninf
l = linf
}
BREAKPOINT {
SOLVE states METHOD cnexp
ek=25*log(ko/ki) :Changed, added, 23/04/2010, Nassi
ik = gkabar*n*l*(v-ek)
}
DERIVATIVE states {
rates(v)
n' = (ninf - n)/taun
l' = (linf - l)/taul
}
PROCEDURE rates(v (mV)) { :callable from hoc
LOCAL a
a = alpn(v)
ninf = 1/(1 + a) : activation variable steady state value
taun = betn(v)/(qt*a0n*(1+a)) : activation variable time constant
if (taun<nmin) {taun=nmin} : time constant not allowed to be less than nmin
a = alpl(v)
linf = 1/(1+ a) : inactivation variable steady state value
taul = 12 (ms)
:taul = 0.26(ms/mV)*(v+50) : inactivation variable time constant
:if (taul<lmin) {taul=lmin} : time constant not allowed to be less than lmin
}
FUNCTION alpn(v(mV)) { LOCAL zeta
zeta = zetan+pw/(1+exp((v-tq)/qq))
UNITSOFF
alpn = exp(1.e-3*zeta*(v-vhalfn)*9.648e4/(8.315*(273.16+celsius)))
UNITSON
}
FUNCTION betn(v(mV)) { LOCAL zeta
zeta = zetan+pw/(1+exp((v-tq)/qq))
UNITSOFF
betn = exp(1.e-3*zeta*gmn*(v-vhalfn)*9.648e4/(8.315*(273.16+celsius)))
UNITSON
}
FUNCTION alpl(v(mV)) {
UNITSOFF
alpl = exp(1.e-3*zetal*(v-vhalfl)*9.648e4/(8.315*(273.16+celsius)))
UNITSON
}
FUNCTION betl(v(mV)) {
UNITSOFF
betl = exp(1.e-3*zetal*gml*(v-vhalfl)*9.648e4/(8.315*(273.16+celsius)))
UNITSON
}