TITLE T calcium current COMMENT from "An Active Membrane Model of the Cerebellar Purkinje Cell 1. Simulation of Current Clamp in Slice" ENDCOMMENT UNITS { (mA) = (milliamp) (mV) = (millivolt) } NEURON { SUFFIX CaT USEION ca READ cai, cao WRITE ica RANGE gcabar, ica, gca, minf, hinf, mexp, hexp } INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)} PARAMETER { v (mV) celsius = 37 (degC) dt (ms) gcabar = .0005 (mho/cm2) eca = 135 (mV) cai = 0.40e-4 (mM) : adjusted for eca=135mV cao = 2.4 (mM) } STATE { m h } ASSIGNED { ica (mA/cm2) gca minf hinf mexp hexp } BREAKPOINT { SOLVE states gca = gcabar * m*h ica = gca* (v-eca) } UNITSOFF INITIAL { rates(v) m = minf h = hinf } PROCEDURE states() { :Computes state variables m, h rates(v) : at the current v and dt. m = m + mexp*(minf-m) h = h + hexp*(hinf-h) } PROCEDURE rates(v) { :Computes rate and other constants at current v. :Call once from HOC to initialize inf at resting v. LOCAL q10, tinc, alpha, beta, sum TABLE minf, mexp, hinf, hexp DEPEND dt, celsius FROM -100 TO 100 WITH 200 q10 = 3^((celsius - 37)/10) tinc = -dt * q10 :"m" calcium activation system alpha = 2.6/(1+exp((v+21)/(-8))) beta = 0.18/(1+exp((v+40)/4)) sum = alpha + beta minf = alpha/sum mexp = 1 - exp(tinc*sum) :"h" calcium inactivation system alpha = 0.0025/(1+exp((v+40)/8)) beta = 0.19/(1+exp((v+50)/(-10))) sum = alpha + beta hinf = alpha/sum hexp = 1 - exp(tinc*sum) } UNITSON