COMMENT High threshold Ca2+ channel 2-state kinetics with sigmoidal voltage-dependence C<->O Goldman-Hodgkin-Katz equations # MODEL | MODEL AUTHOR : D.A. McCormick & J. Huguenard | MODEL DATE : 1992 | MODEL REF : A model of the electrophysiological properties of thalamocortical relay neurons. J Neurophysiol, 1992 Oct, 68(4):1384-400. # EXPERIMENT | EXP AUTHOR : Kay AR; Wong RK | EXP DATE : 1987 | EXP REF : Journal of Physiology, 1987 Nov, 392:603-16. | ANIMAL : guinea-pig | BRAIN REGION : hippocampus | CELL TYPE : Ca1 pyramidal | TECHNIQUE : slices, whole-cell | RECORDING METHOD : voltage-clamp | TEMPERATURE : 20-22 Reference: Destexhe, A., Mainen, Z.F. and Sejnowski, T.J. Synthesis of models for excitable membranes, synaptic transmission and neuromodulation using a common kinetic formalism, Journal of Computational Neuroscience 1: 195-230, 1994. (electronic copy available at http://cns.iaf.cnrs-gif.fr) ENDCOMMENT INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)} NEURON { SUFFIX caL3d USEION ca READ cai, cao WRITE ica RANGE O, C, I RANGE a,b GLOBAL Ra, Rb, q, th, p GLOBAL q10, temp, tadj } UNITS { F = (faraday) (coulomb) R = (k-mole) (joule/degC) (mA) = (milliamp) (mV) = (millivolt) (pS) = (picosiemens) (um) = (micron) (mM) = (milli/liter) } PARAMETER { p = 0.2e-3 (cm/s) : max permeability v (mV) th = 5 (mV) : v 1/2 for on/off q = 13 (mV) : voltage dependence : max rates Ra = 1.6 (/ms) : open (v) Rb = 0.2 (/ms) : close (v) celsius (degC) temp = 22 (degC) : original temp q10 = 3 : temperature sensitivity } ASSIGNED { ica (mA/cm2) cao (mM) cai (mM) a (/ms) b (/ms) tadj } STATE { C O } INITIAL { C = 1 } BREAKPOINT { rates(v) SOLVE kstates METHOD sparse ica = O * p * ghk(v,cai,cao) } KINETIC kstates { ~ C <-> O (a,b) CONSERVE C+O = 1 } PROCEDURE rates(v(mV)) { TABLE a, b DEPEND Ra, Rb, th, celsius, temp, q10 FROM -100 TO 100 WITH 200 tadj = q10 ^ ((celsius - temp)/10 (degC)) a = Ra / (1 + exp(-(v-th)/q)) * tadj b = Rb / (1 + exp((v-th)/q)) * tadj } : Special gear for calculating the Ca2+ reversal potential : via Goldman-Hodgkin-Katz eqn. : [Ca2+]o "cao" and [Ca2+]i "cai" are assumed to be set elsewhere FUNCTION ghk(v(mV), ci(mM), co(mM)) (0.001 coul/cm3) { LOCAL z z = (0.001)*2*F*v/(R*(celsius+273.15)) ghk = (.001)*2*F*(ci*efun(-z) - co*efun(z)) } FUNCTION efun(z) { if (fabs(z) < 1e-4) { efun = 1 - z/2 }else{ efun = z/(exp(z) - 1) } }