TITLE potassium delayed rectifier membrane channels for STh
COMMENT
Delayed rectifier potassium from pyramidal, Traub 1991. He
based them on Sah (1988) data, which were at 22-24degC, but he scaled
them so that they "were fast enough"
How the q10 works: There is a q10 for the rates (alpha and beta's)
called Q10 and a Q10 for the maximum conductance called gmaxQ10. The
q10s should have been measured at specific temperatures temp1 and
temp2 (that are 10degC apart). Ideally, as Q10 is temperature
dependant, we should know these two temperatures. We used to
follow the more formal Arrhenius derived Q10 approach. The
temperature at which this channel's kinetics were recorded is tempb
(base temperature). What we then need to calculate is the desired
rate scale for now working at temperature celsius (rate_k). This was
given by the empirical Arrhenius equation, using the Q10, but now is
using the quick Q10 approximation.
ENDCOMMENT
UNITS {
(mV) = (millivolt)
(mA) = (milliamp)
}
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
NEURON {
SUFFIX KDR
USEION k READ ki,ek WRITE ik
RANGE gk
GLOBAL rest,activate_Q10,Q10,gmaxQ10,rate_k,gmax_k,temp1,temp2,tempb
}
PARAMETER {
v (mV)
dt (ms)
gk = 3.842910637e-03 (mho/cm2)
rest = -60.0 (mV) : for conversion from Traub
ek
ki
celsius
activate_Q10 = 1
Q10 = 1.200000603e+00
gmaxQ10 = 1.200000603e+00
temp1 = 19.0 (degC)
temp2 = 29.0 (degC)
tempb = 23.0 (degC)
}
STATE {
n
}
ASSIGNED {
ik (mA/cm2)
alphan (/ms)
betan (/ms)
rate_k
gmax_k
}
BREAKPOINT {
SOLVE states METHOD cnexp
ik = (gk*gmax_k)*n*(v-ek)
}
UNITSOFF
INITIAL {
LOCAL ktemp,ktempb,ktemp1,ktemp2
if (activate_Q10>0) {
rate_k = Q10^((celsius-tempb)/10)
gmax_k = gmaxQ10^((celsius-tempb)/10)
}else{
: Note, its not 1.0, as we have rescaled the kinetics
: (reverting the scaleing Traub did), the original is
: acheived using this rate
rate_k = 1.60
gmax_k = 1.60
}
settables(v)
n = alphan/(alphan+betan)
}
DERIVATIVE states {
settables(v) :Computes state variables at the current v and dt.
n' = alphan * (1-n) - betan * n
}
PROCEDURE settables(v) { :Computes rate and other constants at current v.
:Call once from HOC to initialize inf at resting v.
:Voltage shift (for temp effects) of 0.60650122.
LOCAL vadj
TABLE alphan, betan DEPEND rest,celsius FROM -100 TO 100 WITH 400
vadj = v - rest + 0.60650122
:"n" potassium activation system
alphan = rate_k * 0.01 * vtrap((35.1-vadj),5.0)
betan = rate_k * 0.156 * exp((20.0-vadj)/40.0)
}
FUNCTION vtrap(x,y) { :Traps for 0 in denominator of rate eqns.
if (fabs(x/y) < 1e-6) {
vtrap = y*(1 - x/y/2)
}else{
vtrap = x/(exp(x/y) - 1)
}
}
UNITSON