TITLE Ca Rtype channel with medium threshold for activation
: used in distal dendritic regions, together with calH.mod, to help
: the generation of Ca++ spikes in these regions
: uses channel conductance (not permeability)
: written by Yiota Poirazi on 11/13/00 poirazi@LNC.usc.edu
:
: updated to use CVode by Carl Gold 08/10/03
: Updated by Maria Markaki 03/12/03
NEURON {
SUFFIX car
USEION ca READ cai, cao WRITE ica
: USEION Ca WRITE iCa VALENCE 2
RANGE gcabar, m, h,ica
RANGE inf, fac, tau
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(molar) = (1/liter)
(mM) = (millimolar)
FARADAY = (faraday) (coulomb)
R = (kmole) (joule/degC)
}
ASSIGNED { : parameters needed to solve DE
ica (mA/cm2)
: iCa (mA/cm2)
inf[2]
tau[2] (ms)
v (mV)
celsius (degC)
cai (mM) : initial internal Ca++ concentration
cao (mM) : initial external Ca++ concentration
}
PARAMETER { : parameters that can be entered when function is called in cellsetup
gcabar = 0 (mho/cm2) : initialized conductance
eca = 140 (mV) : Ca++ reversal potential
}
STATE {
m
h
} : unknown activation and inactivation parameters to be solved in the DEs
INITIAL {
rates(v)
m = 0 : initial activation parameter value
h = 1 : initial inactivation parameter value
}
BREAKPOINT {
SOLVE states METHOD cnexp
:ecar = (1e3) * (R*(celsius+273.15))/(2*FARADAY) * log (cao/cai)
ica = gcabar*m*m*m*h*(v  eca)
}
DERIVATIVE states {
rates(v)
m' = (inf[0]m)/tau[0]
h' = (inf[1]h)/tau[1]
}
PROCEDURE rates(v(mV)) {LOCAL a, b :rest = 70
FROM i=0 TO 1 {
tau[i] = vartau(v,i)
inf[i] = varss(v,i)
}
}
FUNCTION varss(v(mV), i) {
if (i==0) {
varss = 1 / (1 + exp((v+48.5)/(3(mV)))) : Ca activation
}
else if (i==1) {
varss = 1/ (1 + exp((v+53)/(1(mV)))) : Ca inactivation
}
}
FUNCTION vartau(v(mV), i) (ms){
if (i==0) {
vartau = 50(ms) : activation variable time constant
: vartau = 120(ms) : activation variable time constant
}
else if (i==1) {
vartau = 5(ms) : inactivation variable time constant
: vartau = 4(ms) : inactivation variable time constant
}
}
