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 distal region kinetics
: used only in locations > 100 microns from the soma
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
FARADAY = (faraday) (coulomb)
R = (k-mole) (joule/degC)
}
PARAMETER { :parameters that can be entered when function is called in cell-setup
v (mV)
ek = -80 (mV) :K reversal potential (reset in cell-setup.hoc)
celsius = 24 (degC)
: gkabar = 0.008 (mho/cm2) :suggested conductance value
gkabar = 0 (mho/cm2) :initialized conductance
vhalfn = -1 (mV) :activation half-potential
vhalfl = -56 (mV) :inactivation half-potential
a0n = 0.1 (/ms) :parameters used
zetan = -1.8 (1) :in calculation of
zetal = 3 (1) :steady state values
gmn = 0.39 (1) :and time constants
gml = 1 (1)
lmin = 2 (ms)
nmin = 0.1 (ms)
pw = -1 (1)
tq = -40 (mV)
qq = 5 (mV)
q10 = 5 :temperature sensitivity
}
NEURON {
SUFFIX kad
USEION k READ ek WRITE ik
RANGE gkabar,gka, gmax
GLOBAL ninf,linf,taul,taun,lmin
}
STATE { :the unknown parameters to be solved in the DEs
n l
}
ASSIGNED { :parameters needed to solve DE
ik (mA/cm2)
ninf
linf
taul (ms)
taun (ms)
gka (mho/cm2)
gmax (mho/cm2)
}
INITIAL { :initialize the following parameter using rates()
rates(v)
n = ninf
l = linf
gka = gkabar*n*l
ik = gka*(v-ek)
gmax = gka
}
BREAKPOINT {
SOLVE states METHOD cnexp
gka = gkabar*n*l
ik = gka*(v-ek)
if (gka > gmax) {
gmax = gka
}
}
FUNCTION alpn(v(mV)) { LOCAL zeta
zeta = zetan+pw/(1+exp((v-tq)/qq))
alpn = exp((1.e-3)*zeta*(v-vhalfn)*FARADAY/(R*(273.16(degC)+celsius)))
}
FUNCTION betn(v(mV)) { LOCAL zeta
zeta = zetan+pw/(1+exp((v-tq)/qq))
betn = exp((1.e-3)*zeta*gmn*(v-vhalfn)*FARADAY/(R*(273.16(degC)+celsius)))
}
FUNCTION alpl(v(mV)) {
alpl = exp((1.e-3)*zetal*(v-vhalfl)*FARADAY/(R*(273.16(degC)+celsius)))
}
FUNCTION betl(v(mV)) {
betl = exp((1.e-3)*zetal*gml*(v-vhalfl)*FARADAY/(R*(273.16(degC)+celsius)))
}
:if state_borgka is called from hoc, garbage or segmentation violation will
:result because range variables won't have correct pointer. This is because
: only BREAKPOINT sets up the correct pointers to range variables.
DERIVATIVE states { : exact when v held constant; integrates over dt step
rates(v)
n' = (ninf - n)/taun
l' = (linf - l)/taul
}
PROCEDURE rates(v (mV)) { :callable from hoc
LOCAL a,qt
TABLE ninf, taun, linf, taul DEPEND celsius, vhalfn, vhalfl, a0n, zetan, zetal, gmn, gml, lmin, nmin, pw, tq, qq, q10 FROM -100 TO 100 WITH 200
qt = q10^((celsius-24(degC))/10(degC)) : temprature adjastment factor
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 = 0.26(ms/mV)*(v+50(mV)) : inactivation variable time constant
if (taul<lmin) {taul=lmin} : time constant not allowed to be less than lmin
}