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
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
}
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
PARAMETER { :parameters that can be entered when function is called in cell-setup
dt (ms)
v (mV)
ek = -77 (mV) :K reversal potential (reset in cell-setup.hoc)
celsius = 24 (degC)
gkabar = 0 (mho/cm2) :initialized conductance
vhalfn = 11 (mV) :activation half-potential
vhalfl = -56 (mV) :inactivation half-potential
a0n = 0.05 (/ms) :parameters used
zetan = -1.5 (1) :in calculation of
zetal = 3 (1) :steady state values
gmn = 0.55 (1) :and time constants
gml = 1 (1)
lmin = 2 (mS)
nmin = 0.1 (mS)
pw = -1 (1)
tq = -40
qq = 5
q10 = 5 :temperature sensitivity
}
NEURON {
SUFFIX kap
USEION k READ ek WRITE ik
RANGE gkabar,gka
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
taun
gka
}
INITIAL { :initialize the following parameter using rates()
rates(v)
n = ninf
l = linf
gka = gkabar*n*l
ik = gka*(v-ek)
}
BREAKPOINT {
SOLVE states
gka = gkabar*n*l
ik = gka*(v-ek)
}
FUNCTION alpn(v(mV)) { LOCAL zeta
zeta = zetan+pw/(1+exp((v-tq)/qq))
alpn = exp(1.e-3*zeta*(v-vhalfn)*9.648e4/(8.315*(273.16+celsius)))
}
FUNCTION betn(v(mV)) { LOCAL zeta
zeta = zetan+pw/(1+exp((v-tq)/qq))
betn = exp(1.e-3*zeta*gmn*(v-vhalfn)*9.648e4/(8.315*(273.16+celsius)))
}
FUNCTION alpl(v(mV)) {
alpl = exp(1.e-3*zetal*(v-vhalfl)*9.648e4/(8.315*(273.16+celsius)))
}
FUNCTION betl(v(mV)) {
betl = exp(1.e-3*zetal*gml*(v-vhalfl)*9.648e4/(8.315*(273.16+celsius)))
}
LOCAL facn,facl
: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.
PROCEDURE states() { : exact when v held constant; integrates over dt step
rates(v)
n = n + facn*(ninf - n)
l = l + facl*(linf - l)
VERBATIM
return 0;
ENDVERBATIM
}
PROCEDURE rates(v (mV)) { :callable from hoc
LOCAL a,qt
qt = q10^((celsius-24)/10) : 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
facn = (1 - exp(-dt/taun))
a = alpl(v)
linf = 1/(1+ a) : inactivation variable steady state value
taul = 0.26*(v+50) : inactivation variable time constant
if (taul<lmin) {taul=lmin} : time constant not allowed to be less than lmin
facl = (1 - exp(-dt/taul))
}