COMMENT
ca.mod
Uses fixed eca instead of GHK eqn
HVA Ca current
Based on Reuveni, Friedman, Amitai and Gutnick (1993) J. Neurosci. 13:
4609-4621.
Author: Zach Mainen, Salk Institute, 1994, zach@salk.edu
ENDCOMMENT
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
NEURON {
SUFFIX ca
USEION ca READ eca WRITE ica
RANGE m, h, gcaH, icaH, gbar
RANGE minf, hinf, mtau, htau
GLOBAL q10, temp, tadj, vmin, vmax, vshift
}
PARAMETER {
gbar = 0.1 (pS/um2) : 0.12 mho/cm2
vshift = 0 (mV) : voltage shift (affects all)
cao = 2.0 (mM) : external ca concentration
cai (mM)
temp = 23 (degC) : original temp
q10 = 2.3 : temperature sensitivity
v (mV)
dt (ms)
celsius (degC)
vmin = -120 (mV)
vmax = 100 (mV)
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(pS) = (picosiemens)
(um) = (micron)
FARADAY = (faraday) (coulomb)
R = (k-mole) (joule/degC)
PI = (pi) (1)
}
ASSIGNED {
ica (mA/cm2)
icaH (mA/cm2)
gcaH (pS/um2)
eca (mV)
minf hinf
mtau (ms) htau (ms)
tadj
}
STATE { m h }
INITIAL {
trates(v+vshift)
m = minf
h = hinf
}
BREAKPOINT {
SOLVE states METHOD cnexp
gcaH = gbar*m*m*h
icaH = (1e-4) * gcaH * (v - eca)
ica = icaH
}
LOCAL mexp, hexp
:PROCEDURE states() {
: trates(v+vshift)
: m = m + mexp*(minf-m)
: h = h + hexp*(hinf-h)
: VERBATIM
: return 0;
: ENDVERBATIM
:}
DERIVATIVE states {
trates(v+vshift)
m' = (minf-m)/mtau
h' = (hinf-h)/htau
}
PROCEDURE trates(v) {
TABLE minf, hinf, mtau, htau
DEPEND celsius, temp
FROM vmin TO vmax WITH 199
rates(v): not consistently executed from here if usetable == 1
: tinc = -dt * tadj
: mexp = 1 - exp(tinc/mtau)
: hexp = 1 - exp(tinc/htau)
}
PROCEDURE rates(vm) {
LOCAL a, b
tadj = q10^((celsius - temp)/10)
a = 0.055*(-27 - vm)/(exp((-27-vm)/3.8) - 1)
b = 0.94*exp((-75-vm)/17)
mtau = 1/tadj/(a+b)
minf = a/(a+b)
:"h" inactivation
a = 0.000457*exp((-13-vm)/50)
b = 0.0065/(exp((-vm-15)/28) + 1)
htau = 1/tadj/(a+b)
hinf = a/(a+b)
}
FUNCTION efun(z) {
if (fabs(z) < 1e-4) {
efun = 1 - z/2
}else{
efun = z/(exp(z) - 1)
}
}