TITLE n-calcium channel : n-type calcium channel UNITS { (mA) = (milliamp) (mV) = (millivolt) FARADAY = 96520 (coul) R = 8.3134 (joule/degC) KTOMV = .0853 (mV/degC) } PARAMETER { v (mV) celsius (degC) gcanbar=.0003 (mho/cm2) ki=.001 (mM) cai=5.e-5 (mM) cao = 10 (mM) } NEURON { SUFFIX can USEION ca READ cai,cao WRITE ica RANGE gcanbar GLOBAL hinf,minf,taum,tauh } STATE { m h } ASSIGNED { ica (mA/cm2) gcan (mho/cm2) minf hinf taum tauh } INITIAL { rates(v) m = minf h = hinf } BREAKPOINT { SOLVE states METHOD cnexp gcan = gcanbar*m*m*h*h2(cai) ica = gcan*ghk(v,cai,cao) } UNITSOFF FUNCTION h2(cai(mM)) { h2 = ki/(ki+cai) } FUNCTION ghk(v(mV), ci(mM), co(mM)) (mV) { LOCAL nu,f f = KTF(celsius)/2 nu = v/f ghk=-f*(1. - (ci/co)*exp(nu))*efun(nu) } FUNCTION KTF(celsius (degC)) (mV) { KTF = ((25./293.15)*(celsius + 273.15)) } FUNCTION efun(z) { if (fabs(z) < 1e-4) { efun = 1 - z/2 }else{ efun = z/(exp(z) - 1) } } FUNCTION alph(v(mV)) { TABLE FROM -150 TO 150 WITH 200 alph = 1.6e-4*exp(-v/48.4) } FUNCTION beth(v(mV)) { TABLE FROM -150 TO 150 WITH 200 beth = 1/(exp((-v+39.0)/10.)+1.) } FUNCTION alpm(v(mV)) { TABLE FROM -150 TO 150 WITH 200 alpm = 0.1967*(-1.0*v+19.88)/(exp((-1.0*v+19.88)/10.0)-1.0) } FUNCTION betm(v(mV)) { TABLE FROM -150 TO 150 WITH 200 betm = 0.046*exp(-v/20.73) } UNITSON DERIVATIVE states { : exact when v held constant; integrates over dt step rates(v) m' = (minf - m)/taum h' = (hinf - h)/tauh } PROCEDURE rates(v (mV)) { :callable from hoc LOCAL a a = alpm(v) taum = 1/(a + betm(v)) minf = a*taum a = alph(v) tauh = 1/(a + beth(v)) hinf = a*tauh }