TITLE HH fast sodium channel : Hodgkin - Huxley sodium channel with parameters from US Bhalla and JM Bower, : J. Neurophysiol. 69:1948-1983 (1993) : Andrew Davison, The Babraham Institute, 1998. NEURON { SUFFIX nafast USEION na READ ena WRITE ina RANGE gnabar, ina GLOBAL minf, hinf, mtau, htau } UNITS { (mA) = (milliamp) (mV) = (millivolt) } INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)} PARAMETER { v (mV) dt (ms) gnabar = 0.120 (mho/cm2) <0,1e9> ena = 45 (mV) } STATE { m h } ASSIGNED { ina (mA/cm2) minf hinf mtau (ms) htau (ms) } INITIAL { rates(v) m = minf h = hinf } BREAKPOINT { SOLVE states METHOD cnexp ina = gnabar*m*m*m*h*(v - ena) } DERIVATIVE states { rates(v) m' = (minf - m)/mtau h' = (hinf - h)/htau } FUNCTION alp(v(mV),i) (/ms) { if (i==0) { alp = 0.32(/ms)*expM1(-(v *1(/mV) + 42), 4) }else if (i==1){ alp = 0.128(/ms)/(exp((v *1(/mV) + 38)/18)) } } FUNCTION bet(v(mV),i)(/ms) { if (i==0) { bet = 0.28(/ms)*expM1(v *1(/mV) + 15, 5) }else if (i==1){ bet = 4(/ms)/(exp(-(v* 1(/mV) + 15)/5) + 1) } } FUNCTION expM1(x,y) { if (fabs(x/y) < 1e-6) { expM1 = y*(1 - x/y/2) }else{ expM1 = x/(exp(x/y) - 1) } } PROCEDURE rates(v(mV)) {LOCAL a, b TABLE minf, hinf, mtau, htau FROM -100 TO 100 WITH 200 a = alp(v,0) b=bet(v,0) mtau = 1/(a + b) minf = a/(a + b) a = alp(v,1) b=bet(v,1) htau = 1/(a + b) hinf = a/(a + b) }