NEURON {
    SUFFIX aIN_kFast
    USEION k READ ek WRITE ik
    RANGE gmax, ik
}

UNITS {
    (mA) = (milliamp)
    (mV) = (millivolt)
    (S) = (siemens)
}

PARAMETER {
    gmax = 0  (S/cm2)
}

ASSIGNED {
    v (mV)
    ek (mV)
    ik (mA/cm2)
    kf_ninf
    kf_ntau (ms)
     
}

STATE {
    n
}

INITIAL {
    ek = -80.0
    rates()
    n = kf_ninf
    
}

BREAKPOINT {
    SOLVE states METHOD cnexp
    ik = gmax * n  * (v - ek)  
}

DERIVATIVE states {
    rates()
    n' =  ( kf_ninf  -  n ) /  kf_ntau
}

UNITSOFF
PROCEDURE rates() {LOCAL alpha_n, beta_n
    alpha_n = 3.1/(1.0 + exp((-35.5+v)/(-9.3)))
    beta_n = 1.1/(1.0 + exp((0.98+v)/16.19))

    kf_ntau = 1/( alpha_n + beta_n)
    kf_ninf = alpha_n * kf_ntau
}
UNITSON