TITLE Borg-Graham type generic K-A channel

UNITS {
	(mA) = (milliamp)
	(mV) = (millivolt)

}

PARAMETER {
    v (mV)
    ek (mV)
    celsius 	(degC)
    gkabar=.01 (mho/cm2)
    vhalfn=-33.6   (mV)
    vhalfl=-83   (mV)
    a0l=0.08      (/ms)
    a0n=0.02    (/ms)
    zetan=-3    (1)
    zetal=4    (1)
    gmn=0.6   (1)
    gml=1   (1)
}


NEURON {
	SUFFIX borgka
	USEION k READ ek WRITE ik
    RANGE gkabar,gka, ik
    GLOBAL ninf,linf,taul,taun
}

STATE {
	n
    l
}

INITIAL {
    rates(v)
    n=ninf
    l=linf
}

ASSIGNED {
	ik (mA/cm2)
    ninf
    linf      
    taul
    taun
    gka
}

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


FUNCTION alpn(v(mV)) {
  alpn = exp(1.e-3*zetan*(v-vhalfn)*9.648e4/(8.315*(273.16+celsius))) 
}

FUNCTION betn(v(mV)) {
  betn = exp(1.e-3*zetan*gmn*(v-vhalfn)*9.648e4/(8.315*(273.16+celsius))) 
}

FUNCTION alpl(v(mV)) {
  alpl = exp(1.e-3*zetal*(v-vhalfl)*9.648e4/(8.315*(273.16+celsius))) 
}

FUNCTION betl(v(mV)) {
  betl = exp(1.e-3*zetal*gml*(v-vhalfl)*9.648e4/(8.315*(273.16+celsius))) 
}

DERIVATIVE states { 
        rates(v)
        n' = (ninf - n)/taun
        l' = (linf - l)/taul
}

PROCEDURE rates(v (mV)) { :callable from hoc
        LOCAL a,q10
        q10=3^((celsius-30)/10)
        a = alpn(v)
        ninf = 1/(1 + a)
        taun = betn(v)/(q10*a0n*(1+a))
        a = alpl(v)
        linf = 1/(1+ a)
        taul = betl(v)/(q10*a0l*(1 + a))
}