TITLE Fast sodium current COMMENT from "An Active Membrane Model of the Cerebellar Purkinje Cell 1. Simulation of Current Clamp in Slice" ENDCOMMENT UNITS { (mA) = (milliamp) (mV) = (millivolt) } NEURON { SUFFIX NaF USEION na WRITE ina RANGE gnabar, gna, minf, hinf, mexp, hexp } INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)} PARAMETER { v (mV) celsius = 37 (degC) dt (ms) gnabar = 7.5 (mho/cm2) ena = 45 (mV) } STATE { m h } ASSIGNED { ina (mA/cm2) gna minf hinf mexp hexp } BREAKPOINT { SOLVE states gna = gnabar *m*m* m*h ina = gna* (v-ena) } UNITSOFF INITIAL { rates(v) m = minf h = hinf } PROCEDURE states() { :Computes state variables m, h rates(v) : at the current v and dt. m = m + mexp*(minf-m) h = h + hexp*(hinf-h) } PROCEDURE rates(v) { :Computes rate and other constants at current v. :Call once from HOC to initialize inf at resting v. LOCAL q10, tinc, alpha, beta, sum TABLE minf, mexp, hinf, hexp DEPEND dt, celsius FROM -100 TO 100 WITH 200 q10 = 3^((celsius - 37)/10) tinc = -dt * q10 :"m" sodium activation system alpha = 35/exp((v+5)/(-10)) beta = 7/exp((v+65)/20) sum = alpha + beta minf = alpha/sum mexp = 1 - exp(tinc*sum) :"h" sodium inactivation system alpha = 0.225/(1+exp((v+80)/10)) beta = 7.5/exp((v-3)/(-18)) sum = alpha + beta hinf = alpha/sum hexp = 1 - exp(tinc*sum) } UNITSON