TITLE HH k channel channel : Hodgkin - Huxley k channel NEURON { SUFFIX HHk USEION k READ ek WRITE ik RANGE gkbar, ik GLOBAL inf, tau } UNITS { (mA) = (milliamp) (mV) = (millivolt) } PARAMETER { gkbar=.00026 (mho/cm2) <0,1e9> ek (mV) : -77 suggested, default set by NEURON } STATE { n } ASSIGNED { v (mV) celsius (degC) : 16 ik (mA/cm2) inf tau (ms) } INITIAL { rate(v*1(/mV)) n = inf } BREAKPOINT { SOLVE states METHOD cnexp ik = gkbar*n*n*n*n*(v - ek) } DERIVATIVE states { : exact when v held constant rate(v*1(/mV)) n' = (inf - n)/tau } UNITSOFF FUNCTION alp(v(mV)) { LOCAL q10 v = -v - 65 q10 = 3 : 3^((celsius - 6.3)/10) alp = q10 * .01*expM1(v + 10, 10) } FUNCTION bet(v(mV)) { LOCAL q10 v = -v - 65 q10 = 3^((celsius - 6.3)/10) bet = q10 * .125*exp(v/80) } FUNCTION expM1(x,y) { if (fabs(x/y) < 1e-6) { expM1 = y*(1 - x/y/2) }else{ expM1 = x/(exp(x/y) - 1) } } PROCEDURE rate(v) {LOCAL a, b :rest = -70 TABLE inf, tau DEPEND celsius FROM -100 TO 100 WITH 200 a = alp(v)/5 b=bet(v)/5 tau = 1/(a + b) inf = a/(a + b) } UNITSON