TITLE calcium T channel for STh
COMMENT
Low threshold calcium channel (Ttype), Wang et al. 1991
& Coulter et al 1989. The original data was recorded at 2224degC.
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)
FARADAY = (faraday) (coulomb)
R = (kmole) (joule/degC)
}
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
NEURON {
SUFFIX CaT
USEION ca READ cai,cao,eca WRITE ica
RANGE gcaT, iCaT
GLOBAL activate_Q10,Q10,gmaxQ10,rate_k,gmax_k,temp1,temp2,tempb
}
PARAMETER {
v (mV)
dt (ms)
gcaT = 0.001 (mho/cm2)
iCaT = 0.0 (mA/cm2)
eca
cai
cao
celsius
activate_Q10 = 1
Q10 = 1.515804730e+00
gmaxQ10 = 1.515804730e+00
temp1 = 19.0 (degC)
temp2 = 29.0 (degC)
tempb = 23.0 (degC)
}
STATE {
r s d
}
ASSIGNED {
ica (mA/cm2)
ralpha (/ms)
rbeta (/ms)
salpha (/ms)
sbeta (/ms)
dalpha (/ms)
dbeta (/ms)
rate_k
gmax_k
}
BREAKPOINT {
SOLVE states METHOD cnexp
ica = (gcaT*gmax_k)*r*r*r*s*ghkg(v,cai,cao,2)
iCaT = ica
}
UNITSOFF
INITIAL {
LOCAL ktemp,ktempb,ktemp1,ktemp2
if (activate_Q10>0) {
rate_k = Q10^((celsiustempb)/10)
gmax_k = gmaxQ10^((celsiustempb)/10)
}else{
rate_k = 1.0
gmax_k = 1.0
}
settables(v)
r = ralpha/(ralpha+rbeta)
s = (salpha*(dbeta+dalpha)  (salpha*dbeta))/((salpha+sbeta)*(dalpha+dbeta)  (salpha*dbeta))
d = (dbeta*(salpha+sbeta)  (salpha*dbeta))/((salpha+sbeta)*(dalpha+dbeta)  (salpha*dbeta))
}
DERIVATIVE states {
settables(v) :Computes state variables at the current v and dt.
r' = ((ralpha*(1r))  (rbeta*r))
d' = ((dbeta*(1sd))  (dalpha*d))
s' = ((salpha*(1sd))  (sbeta*s))
}
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 1.9278 added
LOCAL bd
TABLE ralpha, rbeta, salpha, sbeta, dalpha, dbeta DEPEND celsius FROM 100 TO 100 WITH 400
:"r" CaT activation system
ralpha = rate_k * 1.0/(1.7+exp((v + 26.2722)/13.5))
rbeta = rate_k * exp((v + 61.0722)/7.8)/(exp((v + 26.8722)/13.1)+1.7)
:"s" CaT fast inactivation system
salpha = rate_k * exp((v + 158.3722)/17.8)
sbeta = rate_k * (sqrt(0.25+exp((v + 81.5722)/6.3))0.5) * (exp((v + 158.3722)/17.8))
:"d" CaT slow inactivation system
bd = sqrt(0.25+exp((v + 81.5722)/6.3))
dalpha = rate_k * (1.0+exp((v + 35.4722)/30.0))/(240.0*(0.5+bd))
dbeta = rate_k * (bd0.5)*dalpha
}
UNITSON
INCLUDE "ghk.inc"
