TITLE Slow Cadependent cation current
:
: Ca++ dependent nonspecific cation current ICAN
: Differential equations
:
: This file was taken the study of Zhu et al.: Neuroscience 91, 14451460, 1999,
: where kinetics were based on Partridge & Swandulla, TINS 11: 6972, 1988
: Modified by Geir Halnes, Norwegian University of Life Sciences, June 2011
: (using only 1 of the two calcium pools applied by Zhu et al. 99)
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
NEURON {
THREADSAFE
SUFFIX ican
USEION other WRITE iother VALENCE 1
USEION Ca READ Cai VALENCE 2
RANGE gbar, i, g
GLOBAL m_inf, tau_m, beta, cac, taumin, erev, x
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(molar) = (1/liter)
(mM) = (millimolar)
}
PARAMETER {
v (mV)
celsius = 36 (degC)
erev = 10 (mV)
Cai = .00005 (mM) : initial [Ca]i = 50 nM
gbar = 1e5 (mho/cm2)
beta = 0.003
cac = 1.1e4 (mM) : middle point of activation fct
taumin = 0.1 (ms) : minimal value of time constant
x = 8
}
STATE {
m
}
INITIAL {
: activation kinetics are assumed to be at 22 deg. C
: Q10 is assumed to be 3
:
VERBATIM
Cai = _ion_Cai;
ENDVERBATIM
tadj = 3.0 ^ ((celsius22.0)/10)
evaluate_fct(v,Cai)
m = m_inf
}
ASSIGNED {
i (mA/cm2)
iother (mA/cm2)
g (mho/cm2)
m_inf
tau_m (ms)
tadj
}
BREAKPOINT {
SOLVE states METHOD cnexp
g = gbar * m*m
i = g * (v  erev)
iother = i
}
DERIVATIVE states {
evaluate_fct(v,Cai)
m' = (m_inf  m) / tau_m
}
UNITSOFF
PROCEDURE evaluate_fct(v(mV),Cai(mM)) { LOCAL alpha
alpha = beta * (Cai/cac)^x
tau_m = 1 / (alpha + beta) / tadj
m_inf = alpha / (alpha + beta)
if(tau_m < taumin) { tau_m = taumin } : min value of time cst
}
UNITSON
