TITLE Low threshold calcium current
COMMENT
12/1/2005 NTC Made compatible with adaptive integration
Unused stuff removed
ENDCOMMENT
: Modified by Steven Prescott based on current described below
: Prescott and De Koninck. 2005. J Neurosci 25: 47434754
: low threshold, transient calcium current,
: reproduces ttxinsensitive rebound depolarization seen in tonic spinal lamina I neurons
:
: original current described below...
: Ca++ current responsible for low threshold spikes (LTS)
: RETICULAR THALAMUS
: Differential equations
:
: Model of Huguenard & McCormick, J Neurophysiol 68: 13731383, 1992.
: The kinetics is described by standard equations (NOT GHK)
: using a m2h format, according to the voltageclamp data
: (whole cell patch clamp) of Huguenard & Prince, J Neurosci.
: 12: 38043817, 1992. The model was introduced in Destexhe et al.
: J. Neurophysiology 72: 803818, 1994.
:
:  Kinetics adapted to fit the Tchannel 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
NEURON {
SUFFIX CaT
USEION ca READ cai, cao WRITE ica
RANGE gcabar, m_inf, tau_m, h_inf, tau_h, shift
RANGE vsm, vsh
RANGE ica
}
UNITS {
(molar) = (1/liter)
(mV) = (millivolt)
(mA) = (milliamp)
(mM) = (millimolar)
FARADAY = (faraday) (coulomb)
R = (kmole) (joule/degC)
}
PARAMETER {
v (mV)
celsius (degC)
gcabar = .00003 (mho/cm2)
shift = 2 (mV) : screening charge for Ca_o = 2 mM
cai (mM)
cao (mM)
vsm = 20 (mV) : shift activation curve to left
vsh = 20 (mV) : shift inactivation curve to left
}
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 cnexp
carev = (1e3) * (R*(celsius+273.15))/(2*FARADAY) * log (cao/cai)
ica = gcabar * m*m*h * (vcarev)
}
DERIVATIVE castate {
evaluate_fct(v)
m'= (m_infm) / tau_m
h'= (h_infh) / tau_h
}
UNITSOFF
INITIAL {
:
: Activation functions and kinetics were obtained from
: Huguenard & Prince, and were at 2325 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 ^ ((celsius24)/10)
phi_h = 3.0 ^ ((celsius24)/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+vsm+50)/(7.4)) )
h_inf = 1.0 / ( 1 + exp((v+shift+vsh+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
