TITLE calcium HVA channels for STh
COMMENT
High threshold calcium channel (N/L-type), Brown et al. 1993. & Fox
et al. (1989). Both done at temperature 22degC.
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.
Adding CaL [Ca]i dependent inactivation. This is only for the L-type
component, and is called inactivation variable 'h'.
ENDCOMMENT
UNITS {
(mM) = (milli/liter)
(mV) = (millivolt)
(mA) = (milliamp)
FARADAY = (faraday) (coulomb)
R = (k-mole) (joule/degC)
}
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
NEURON {
SUFFIX HVA
USEION ca READ cai,cao,eca WRITE ica
RANGE gcaN, gcaL, iNCa, iLCa
GLOBAL inactLtau,inactLmax,activate_Q10,Q10,gmaxQ10,rate_k,gmax_k,temp1,temp2,tempb
}
PARAMETER {
v (mV)
dt (ms)
gcaL = 0.002 (mho/cm2)
gcaN = 0.012 (mho/cm2)
iNCa = 0.0 (mA/cm2)
iLCa = 0.0 (mA/cm2)
inactLtau = 1220.0 (ms)
inactLmax = 5.291291201e-01
eca
cai
cao
celsius
activate_Q10 = 1
Q10 = 1.948259241e+00
gmaxQ10 = 1.948259241e+00
temp1 = 20.0 (degC)
temp2 = 30.0 (degC)
tempb = 22.0 (degC)
}
STATE {
q u h
}
ASSIGNED {
ica (mA/cm2)
qinf
uinf
hinf
qtau (ms)
utau (ms)
htau (ms)
rate_k
gmax_k
}
BREAKPOINT {
LOCAL vghk
SOLVE states METHOD cnexp
vghk = ghkg(v,cai,cao,2)
iNCa = gmax_k*(gcaN * u)*q*q*vghk
iLCa = gmax_k*(gcaL)*q*q*h*vghk
ica = iNCa + iLCa
}
INITIAL {
LOCAL ktemp,ktempb,ktemp1,ktemp2
if (activate_Q10>0) {
rate_k = Q10^((celsius-tempb)/10)
gmax_k = gmaxQ10^((celsius-tempb)/10)
}else{
rate_k = 1.0
gmax_k = 1.0
}
settables(v)
q = qinf
u = uinf
setCadepLinact(cai)
h = hinf
}
DERIVATIVE states {
settables(v)
q' = (qinf-q)/qtau
u' = (uinf-u)/utau
setCadepLinact(cai)
h' = (hinf-h)/htau
}
PROCEDURE settables(v) { :Computes rate and other constants at current v.
:Call once from HOC to initialize inf at resting v.
:Voltage shifts (for temp effects) of -8.25 and -14.67 added respt.
TABLE qinf, qtau, uinf, utau DEPEND celsius FROM -100 TO 100 WITH 400
:"q" N/L Ca activation system
qinf = 1.0/(1.0 + exp((-16.3547869 - v)/11.3))
qtau = (1.25/(cosh(-0.031 * (v + 28.8547869)))) /rate_k
:"u" N inactivation system - voltage dependent.
uinf = 1.0/(1.0 + exp((v + 45.3326653)/12.5))
utau = (98.0 + cosh(0.021*(24.7673347-v))) /rate_k
}
PROCEDURE setCadepLinact(cai) { : set Ca dependent L-type calcium channel inactivation
:"h" L inactivation system - [Ca]i dependent.
hinf = inactLmax+((1.0-inactLmax)/(1.0 + exp((cai-0.7)/0.15)))
htau = inactLtau /rate_k
}
INCLUDE "ghk.inc"