TITLE Fast transient sodium current NEURON { THREADSAFE SUFFIX naf USEION na READ ena WRITE ina RANGE gbar, gna, ina, mVhalf, hVhalf, mSlope, hSlope, taum, tauh, taun, base, factor POINTER pka } UNITS { (S) = (siemens) (mV) = (millivolt) (mA) = (milliamp) } PARAMETER { gbar = 0.0 (S/cm2) q = 1.8 mVhalf = -25.0 (mV) hVhalf = -62.0 (mV) mSlope = -9.2 (mV) hSlope = 6.0 (mV) taum = 0.09 (ms) taun = 0.34 (ms) tauh = 0.34 (ms) base = 0.0 : set in simulation file (if used) factor = 0.0 : set in simulation file (if used) } ASSIGNED { v (mV) ena (mV) ina (mA/cm2) gna (S/cm2) minf mtau (ms) hinf htau (ms) pka (1) } STATE { m h } BREAKPOINT { SOLVE states METHOD cnexp gna = modulation() * gbar*m*m*m*h ina = gna*(v-ena) } DERIVATIVE states { rates() m' = (minf-m)/mtau*q h' = (hinf-h)/htau*q } INITIAL { rates() m = minf h = hinf } PROCEDURE rates() { UNITSOFF minf = 1 / (1 + exp( (v-mVhalf) / mSlope ) ) hinf = 1 / (1 + exp( (v-hVhalf) / hSlope ) ) mtau = 0.38 + 1/( 0.6*exp((v-(-58.0))/8.0) + 1.8*exp((v-(-58.0))/(-35.0)) ) if (v < - 60) { htau = 3.4 + 0.015*v }else{ htau = 0.56 + 1.1/(1+exp((v-(-48))/15.0)) + 1.2/(1+exp((v-(-48))/4.0)) } :mtau = 0.13 +1/(0.6*exp((v-(-58))/taum)+1.8*exp((v-(-58))/(taun))) :htau = 0.14 +1.2/(1+exp((v-(-32))/tauh)) UNITSON } FUNCTION modulation() { : returns modulation factor modulation = 1 + factor * (pka - base) } COMMENT TODO: update kintetics of inactivation gate below -60 mV, from linear to sigmoidal? -------------------------------------------------------------------------------------- Original data by Ogata (1990), guinea pig, 22 C. Genesis implementation by Kai Du , MScell v9.5. NEURON implementation by Alexander Kozlov , smooth fit of mtau and htau. Updates by Robert Lindroos channel kinetics updated so that natural instead of base 10 logarithm is used for values in Ogata 1990. This also reduces the AHP and spike frequency. The revision of Ogata 1990, was done following a scanning of m and h gate parameters that reduced the AHP magnitude. Q factor of 1.8 used. Based on "The effect of temperature on Na currents in rat myelinated nerve fibres" -> Q10 between 40 and 20 C 1.8-2.1 lowest value chousen since spiking is still intact and this make the cell fire slightly slower ENDCOMMENT