TITLE Low threshold calcium current
:
: Ca++ current responsible for low threshold spikes (LTS)
: RETICULAR THALAMUS
: Differential equations
:
: Model of Huguenard & McCormick, J Neurophysiol 68: 1373-1383, 1992.
: The kinetics is described by standard equations (NOT GHK)
: using a m2h format, according to the voltage-clamp data
: (whole cell patch clamp) of Huguenard & Prince, J Neurosci.
: 12: 3804-3817, 1992. The model was introduced in Destexhe et al.
: J. Neurophysiology 72: 803-818, 1994.
:
: - Kinetics adapted to fit the T-channel of reticular neuron
: - Q10 changed to 5 and 3
: - Time constant tau_h fitted from experimental data
: - shift parameter for screening charge
:
: ACTIVATION FUNCTIONS FROM EXPERIMENTS (NO CORRECTION)
:
: Reversal potential taken from Nernst Equation
:
: Written by Alain Destexhe, Salk Institute, Sept 18, 1992
:
: Modifications by Arthur Houweling for use in MyFirstNEURON
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
NEURON {
SUFFIX iT2
USEION ca READ cai, cao WRITE ica
RANGE gcabar, m_inf, tau_m, h_inf, tau_h, shift
RANGE ica
}
UNITS {
(molar) = (1/liter)
(mV) = (millivolt)
(mA) = (milliamp)
(mM) = (millimolar)
FARADAY = (faraday) (coulomb)
R = (k-mole) (joule/degC)
}
PARAMETER {
v (mV)
celsius (degC)
dt (ms)
gcabar = .00175 (mho/cm2)
shift = 2 (mV) : screening charge for Ca_o = 2 mM
cai (mM)
cao (mM)
}
STATE {
m h
}
ASSIGNED {
ica (mA/cm2)
carev (mV)
m_inf
tau_m (ms)
h_inf
tau_h (ms)
phi_m
phi_h
}
BREAKPOINT {
SOLVE castate :METHOD euler
carev = (1e3) * (R*(celsius+273.15))/(2*FARADAY) * log (cao/cai)
ica = gcabar * m*m*h * (v-carev)
}
:DERIVATIVE castate {
: evaluate_fct(v)
:
: m'= (m_inf-m) / tau_m
: h'= (h_inf-h) / tau_h
:}
PROCEDURE castate() {
evaluate_fct(v)
m= m + (1-exp(-dt/tau_m))*(m_inf-m)
h= h + (1-exp(-dt/tau_h))*(h_inf-h)
}
UNITSOFF
INITIAL {
:
: Activation functions and kinetics were obtained from
: Huguenard & Prince, and were at 23-25 deg.
: Transformation to 36 deg assuming Q10 of 5 and 3 for m and h
: (as in Coulter et al., J Physiol 414: 587, 1989)
:
phi_m = 5.0 ^ ((celsius-24)/10)
phi_h = 3.0 ^ ((celsius-24)/10)
evaluate_fct(v)
m = m_inf
h = h_inf
}
PROCEDURE evaluate_fct(v(mV)) {
:
: Time constants were obtained from J. Huguenard
:
m_inf = 1.0 / ( 1 + exp(-(v+shift+50)/7.4) )
h_inf = 1.0 / ( 1 + exp((v+shift+78)/5.0) )
tau_m = ( 3 + 1.0 / ( exp((v+shift+25)/10) + exp(-(v+shift+100)/15) ) ) / phi_m
tau_h = ( 85 + 1.0 / ( exp((v+shift+46)/4) + exp(-(v+shift+405)/50) ) ) / phi_h
}
UNITSON