TITLE Low voltage activated calcium current (CaLVA) of deep cerebellar nucleus (DCN) neuron COMMENT This mechanism and the other calcium channel (CaHVA.mod) are the only channel mechanisms of the DCN model that use the GHK mechanism to calculate reversal potential. Thus, extracellular Ca concentration is of importance and shall be set from hoc to 2mM, using: "calo0_ca_ion = 2". The calcium that this channel lets through feeds into the CalConc.mod mechanism while calcium entry via the CaHVA channel is tracked by CalConc.mod. ENDCOMMENT NEURON { SUFFIX CaLVA USEION cal READ cali, calo WRITE ical VALENCE 2 RANGE perm, ical, m, h, cali GLOBAL qdeltat } UNITS { (mA) = (milliamp) (mV) = (millivolt) (molar) = (1/liter) (mM) = (millimolar) } PARAMETER { qdeltat = 1 perm = 1 (cm/seconds) } ASSIGNED { v (mV) cali (mM) calo (mM) ical (mA/cm2) minf hinf taum (ms) tauh (ms) celsius (degC) T (kelvin) A (1) } STATE { m h } INITIAL { T = 273.15 + celsius rate(v) m = minf h = hinf } BREAKPOINT { SOLVE states METHOD cnexp A = getGHKexp(v) : "4.47814e6 * v / T" in the following is the simplification of the GHK : current equation's (z^2 * F^2 * (0.001) * v) / (R * T). [*(0.001) is to get : volt from NEURON's mV.] Together with the simplification in getGHKexp() : (below), this speeds up the whole DCN simulation (without synapses) by 8%. : The division of the calcium concentrations (mM) by 1000 gives molar as : required by the GHK current equation. ical = perm * m*m * h * (4.47814e6 * v / T) * ((cali/1000) - (calo/1000) * A) / (1 - A) } DERIVATIVE states { rate(v) m' = (minf - m)/taum h' = (hinf - h)/tauh } PROCEDURE rate(v(mV)) { TABLE minf, taum, hinf, tauh FROM -150 TO 100 WITH 300 minf = 1 / (1 + exp((v + 56) / -6.2)) taum = 0.333 / (exp((v + 131) / -16.7) + exp((v + 15.8) / 18.2)) + 0.204 taum = taum / qdeltat hinf = 1 / (1 + exp((v + 80) / 4)) if (v < -81) { tauh = 0.333 * exp((v + 466) / 66) } else { tauh = 0.333 * exp((v + 21) / -10.5) + 9.32 } tauh = tauh / qdeltat } FUNCTION getGHKexp(v(mV)) { TABLE DEPEND T FROM -150 TO 100 WITH 300 getGHKexp = exp(-23.20764929 * v / T): =the calculated values of : getGHKexp = exp((-z * F * (0.001) * v) / (R * T)). }