TITLE Ca Ltype channel with high treshold of activation
: inserted in distal dendrites to account for distally
: restricted initiation of Ca++ spikes
: uses channel conductance (not permeability)
: written by Yiota Poirazi, 1/8/00 poirazi@LNC.usc.edu
NEURON {
SUFFIX calH
USEION ca READ eca WRITE ica
RANGE gcalbar, m, h
RANGE inf, fac, tau
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
}
PARAMETER { : parameters that can be entered when function is called in cellsetup
v (mV)
celsius = 34 (degC)
dt (ms)
gcalbar = 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
ASSIGNED {
ica (mA/cm2)
inf[2]
tau[2]
}
INITIAL {
m = 0 : initial activation parameter value
h = 1 : initial inactivation parameter value
rate(v)
}
BREAKPOINT {
SOLVE state METHOD cnexp
ica = gcalbar*m*m*m*h*(v  eca)
}
DERIVATIVE state {
rate(v)
m' = (inf[0]m)/tau[0]
h' = (inf[1]h)/tau[1]
}
PROCEDURE rate(v (mV)) { :callable from hoc
FROM i=0 TO 1 {
tau[i] = vartau(v,i)
inf[i] = varss(v,i)
}
}
FUNCTION varss(v, i) {
if (i==0) {
varss = 1 / (1 + exp((v+37)/(1))) : Ca activation
}
else if (i==1) {
varss = 1 / (1 + exp((v+41)/(0.5))) : Ca inactivation
}
}
FUNCTION vartau(v, i) {
if (i==0) {
vartau = 3.6 : activation variable time constant
}
else if (i==1) {
: vartau = 25 : inactivation variable time constant
vartau = 29 : inactivation variable time constant
}
}
