TITLE calcium accumulation for STh
COMMENT
Calcium accumulation into a volume of area*depth next to the
membrane with an exponential decay (time constant tau) to resting
level (given by the global calcium variable cai0_ca_ion).
How the q10 works:
There is a q10 for the rates (alpha and beta's) called Q10. 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 are going 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 is given
by the empirical Arrhenius equation, using the Q10.
ENDCOMMENT
NEURON {
SUFFIX Cacum
USEION ca READ ica WRITE cai
GLOBAL con,cai0,buftau,activate_Q10,Q10,rate_k,temp1,temp2,tempb,depth
}
UNITS {
(mM) = (milli/liter)
(mA) = (milliamp)
F = (faraday) (coulombs) : Faradays constant
}
PARAMETER {
v (mV)
dt (ms)
con = 0.0 : conversion constant (see INITIAL block)
Avo = 6.02e23 : Avogadro's number
elc = 1.602e19 (coulombs) : elementrary charge
depth = 200.0 (nm) : assume volume = area*depth
cai0 = 0.0001(mM) : replace cai0_ca_ion
buftau = 1.857456645e+02 (ms)
cai0_ca_ion
celsius
activate_Q10 = 1
Q10 = 1.2
temp1 = 19.0 (degC)
temp2 = 29.0 (degC)
tempb = 23.0 (degC)
}
ASSIGNED {
ica (mA/cm2)
tau (ms)
rate_k
}
STATE {
cai (mM)
}
BREAKPOINT {
SOLVE integrate METHOD cnexp
}
UNITSOFF
INITIAL {
LOCAL ktemp,ktempb,ktemp1,ktemp2
if (activate_Q10>0) {
ktemp = celsius+273.0
ktempb = tempb+273.0
ktemp1 = temp1+273.0
ktemp2 = temp2+273.0
rate_k = exp( log(Q10)*((1/ktempb)(1/ktemp))/((1/ktemp1)(1/ktemp2)) )
}else{
rate_k = 1.0
}
con=1e7/(depth*2.0*Avo*elc) : UNITS (derivation)
: ica = (mA/cm2)
: = (A/1e3cm2)
: = ((C/s)/1e3cm2)
: depth = (nm) = (1e7cm)
: ica/depth = ((C/s)/1e3cm2) * 1/(1e7cm)
: = ((C/s)/1e3cm2) * 1e7/(cm)
: = (1e7(C/s) * 1/(1e3cm3))
: = (1e7(C/s) * 1/(litres))
: 1e7*ica/depth = ((C/s) * 1/(litres))
: = ((C/litres) * 1/(s))
: = ((C/litres) * 1/(1e3msec))
: = ((C/litres) * 1e3/(msec))
: 1e4*ica/depth = ((C/litres) * 1/(msec))
: 1/(2*Avo*elc) = (mol/C)
: = (1e3mmol/C)
: 1e3/(2*Avo*elc) = (mmol/C)
: 1e4*ica/depth * 1e3/(2*Avo*elc) = ((C/litres) * 1/(msec))
: * (mmol/C)
: ica*1e7/(depth*2*Avo*elc) = (mmol/litres) * (1/msec)
: ica*con = (mM) * (1/msec)
tau=buftau/rate_k
cai=cai0
}
DERIVATIVE integrate {
cai' = ica*con + (cai0  cai)/tau
}
UNITSON
