TITLE transient and low threshold calcium current (T-current) INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)} NEURON { SUFFIX CaT : USEION ca READ cai,cao : USEION Ca WRITE iCa VALENCE 2 USEION Ca READ Cai, Cao WRITE iCa VALENCE 2 RANGE minf, mtau, hinf, htau, iCa GLOBAL pmax } UNITS { (mA) = (milliamp) (mV) = (millivolt) (mM) = (milli/liter) FARADAY = 96489 (coul) R = 8.314 (volt-coul/degC) } PARAMETER { v (mV) celsius (degC) : cai (mM) : cao (mM) Cai (mM) Cao (mM) pmax = 4e-7 (cm/s) } STATE { m h } ASSIGNED { iCa (mA/cm2) mtau (ms) minf hinf htau (ms) } BREAKPOINT { SOLVE state METHOD cnexp iCa = pmax * m*m*m*h*ghk(v,Cai,Cao,2) : iCa = pmax * m*m*m*h*ghk(v,0.001,Cao,2) } DERIVATIVE state { rates(v) m'= (minf-m) / mtau h'= (hinf-h) / htau } INITIAL { rates(v) m = minf h = hinf } FUNCTION ghk( v(mV), ci(mM), co(mM), z) (millicoul/cm3) { LOCAL e, w w = v * (.001) * z*FARADAY / (R*(celsius+273.16)) if (fabs(w)>1e-4) { e = w / (exp(w)-1) } else : denominator is small -> Taylor series { e = 1-w/2 } ghk = - (.001) * z*FARADAY * (co-ci*exp(w)) * e } FUNCTION_TABLE tabmtau(v(mV)) (ms) FUNCTION_TABLE tabhtau(v(mV)) (ms) UNITSOFF PROCEDURE rates(v(mV)) { mtau = tabmtau(v) htau = tabhtau(v) minf = 1 / (1+exp((v+51.73)/-6.53)) hinf = 1 / (1+exp((v+80)/6.7)) } : UNITSON