: \$Id: ICAN_destexhe.mod,v 1.4 1994/04/14 01:27:53 billl Exp \$ TITLE Slow Ca-dependent cation current : : Ca++ dependent nonspecific cation current ICAN : Differential equations : : Model of Destexhe, 1992. Based on a first order kinetic scheme : + n cai <-> (alpha,beta) : : Following this model, the activation fct will be half-activated 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) : --------------------------------------------- : : Kinetics based on: Partridge & Swandulla, TINS 11: 69-72, 1988. : : This current has the following properties: : - inward current (non specific for cations Na, K, Ca, ...) : - activated by intracellular calcium : - NOT voltage dependent : : Written by Alain Destexhe, Salk Institute, Dec 7, 1992 : INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)} NEURON { SUFFIX ican USEION n READ en WRITE in VALENCE 1 USEION ca READ cai RANGE gbar, m_inf, tau_m GLOBAL beta, cac, taumin } UNITS { (mA) = (milliamp) (mV) = (millivolt) (molar) = (1/liter) (mM) = (millimolar) } PARAMETER { v (mV) celsius = 36 (degC) en (mV) cai = .00005 (mM) : initial [Ca]i = 50 nM gbar = 1e-5 (mho/cm2) beta = 2.5 (1/ms) : backward rate constant cac = 1e-4 (mM) : middle point of activation fct taumin = 0.1 (ms) : minimal value of time constant } STATE { m } ASSIGNED { in (mA/cm2) m_inf tau_m (ms) tadj } BREAKPOINT { SOLVE states METHOD cnexp in = gbar * m*m * (v - en) } DERIVATIVE states { evaluate_fct(v,cai) m' = (m_inf - m) / tau_m } UNITSOFF INITIAL { evaluate_fct(v,cai) m = m_inf : : activation kinetics are assumed to be at 22 deg. C : Q10 is assumed to be 3 : tadj = 3.0 ^ ((celsius-22.0)/10) } PROCEDURE evaluate_fct(v(mV),cai(mM)) { LOCAL alpha2 alpha2 = beta * (cai/cac)^2 tau_m = 1 / (alpha2 + beta) / tadj m_inf = alpha2 / (alpha2 + beta) if(tau_m < taumin) { tau_m = taumin } : min value of time cst } UNITSON