TITLE Slow Cadependent potassium current
:
: Ca++ dependent K+ current IC responsible for slow AHP
: Differential equations
:
: Model based on a first order kinetic scheme
:
: + n cai <> (alpha,beta)
:
: Following this model, the activation fct will be halfactivated at
: a concentration of Cai = (beta/alpha)^(1/n) = cac (parameter)
:
: The mod file is here written for the case n=2 (2 binding sites)
: 
:
: This current models the "slow" IK[Ca] (IAHP):
:  potassium current
:  activated by intracellular calcium
:  NOT voltage dependent
:
: A minimal value for the time constant has been added
:
: Ref: Destexhe et al., J. Neurophysiology 72: 803818, 1994.
: See also: http://www.cnl.salk.edu/~alain , http://cns.fmed.ulaval.ca
: modifications by Yiota Poirazi 2001 (poirazi@LNC.usc.edu)
: taumin = 0.5 ms instead of 0.1 ms
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
NEURON {
SUFFIX iKCa
USEION k READ ek WRITE ik
USEION ca READ cai
RANGE gbar, m_inf, tau_m
GLOBAL beta, cac
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(molar) = (1/liter)
(mM) = (millimolar)
}
PARAMETER {
v (mV)
celsius = 36 (degC)
ek = 80 (mV)
cai = 50.0e6 (mM) : initial [Ca]i
gbar = 0.002 (mho/cm2)
beta = 0.03 (1/ms) : backward rate constant
:cac = 0.025 (mM) : middle point of activation fct
cac = 0.010 (mM) : middle point of activation fct
taumin = 0.1 (ms) : minimal value of the time cst
}
STATE {m} : activation variable to be solved in the DEs
ASSIGNED { : parameters needed to solve DE
ik (mA/cm2)
m_inf
tau_m (ms)
tadj
}
BREAKPOINT {
SOLVE states METHOD derivimplicit
ik = gbar * m*m*m * (v  ek) : potassium current induced by this channel
}
DERIVATIVE states {
evaluate_fct(v,cai)
m' = (m_inf  m) / tau_m
}
UNITSOFF
INITIAL {
:
: activation kinetics are assumed to be at 22 deg. C
: Q10 is assumed to be 3
:
tadj = 3 ^ ((celsius22.0)/10) : temperaturedependent adjastment factor
evaluate_fct(v,cai)
m = m_inf
}
PROCEDURE evaluate_fct(v(mV),cai(mM)) { LOCAL car
car = (cai/cac)^2
m_inf = car / ( 1 + car ) : activation steady state value
tau_m = 1 / beta / (1 + car) / tadj
if(tau_m < taumin) { tau_m = taumin } : activation min value of time cst
}
UNITSON
