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112 lines
2.1 KiB
112 lines
2.1 KiB
2 years ago
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TITLE Slow Ca-dependent potassium current
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:
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: Ca++ dependent K+ current IC responsible for slow AHP
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: Differential equations
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:
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: Model based on a first order kinetic scheme
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:
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: <closed> + n cai <-> <open> (alpha,beta)
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:
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: Following this model, the activation fct will be half-activated at
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: a concentration of Cai = (beta/alpha)^(1/n) = cac (parameter)
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:
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: The mod file is here written for the case n=2 (2 binding sites)
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: ---------------------------------------------
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:
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: This current models the "slow" IK[Ca] (IAHP):
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: - potassium current
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: - activated by intracellular calcium
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: - NOT voltage dependent
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:
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: A minimal value for the time constant has been added
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:
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: Ref: Destexhe et al., J. Neurophysiology 72: 803-818, 1994.
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:
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: Modifications by Arthur Houweling for use in MyFirstNEURON
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INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
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NEURON {
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THREADSAFE
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SUFFIX kpksk
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USEION k READ ek WRITE ik
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USEION ca READ cai
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RANGE m_inf, tau_m, gbar, gk
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GLOBAL beta, cac
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RANGE ik
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}
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UNITS {
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(mA) = (milliamp)
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(mV) = (millivolt)
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(molar) = (1/liter)
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(mM) = (millimolar)
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}
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PARAMETER {
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v (mV)
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celsius (degC)
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dt (ms)
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ek (mV)
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cai (mM)
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gbar = .01 (mho/cm2)
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beta = 0.002 (1/ms) : backward rate constant
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cac = 0.010 (mM) : middle point of activation fct
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taumin = 0.1 (ms) : minimal value of the time cst
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}
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STATE {
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m
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}
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ASSIGNED {
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ik (mA/cm2)
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gk (mho/cm2)
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m_inf
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tau_m (ms)
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tadj ()
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}
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BREAKPOINT {
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SOLVE states :METHOD euler
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gk = gbar * m*m
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ik = gk * (v - ek)
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}
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:DERIVATIVE states {
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: evaluate_fct(v,cai)
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:
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: m'= (m_inf-m) / tau_m
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:}
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PROCEDURE states() {
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evaluate_fct(v,cai)
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m= m + (1-exp(-dt/tau_m))*(m_inf-m)
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}
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INITIAL {
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:
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: activation kinetics are assumed to be at 22 deg. C
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: Q10 is assumed to be 3
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:
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tadj = 3 ^ ((celsius-22.0)/10 (degC))
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evaluate_fct(v,cai)
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m = m_inf
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}
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PROCEDURE evaluate_fct(v(mV),cai(mM)) { LOCAL car
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car = (cai/cac)^2
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m_inf = car / ( 1 + car )
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tau_m = 1 / beta / (1 + car) / tadj
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if(tau_m < taumin) { tau_m = taumin } : min value of time cst
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}
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