TITLE Ca R-type channel with medium threshold for activation : used in somatic regions. It has lower threshold for activation/inactivation : and slower activation time constant : than the same mechanism in dendritic regions : uses channel conductance (not permeability) : written by Yiota Poirazi on 3/12/01 poirazi@LNC.usc.edu NEURON { SUFFIX somacar USEION ca READ eca WRITE ica RANGE gcabar, m, h, g, gmax RANGE inf, tau } UNITS { (mA) = (milliamp) (mV) = (millivolt) } PARAMETER { : parameters that can be entered when function is called in cell-setup v (mV) celsius = 34 (degC) gcabar = 0 (mho/cm2) : initialized conductance eca = 140 (mV) : Ca++ reversal potential } STATE { m h } : unknown activation and inactivation parameters to be solved in the DEs ASSIGNED { : parameters needed to solve DE ica (mA/cm2) inf[2] tau[2] (ms) g (mho/cm2) gmax (mho/cm2) } BREAKPOINT { SOLVE states METHOD cnexp g = gcabar*m*m*m*h ica = g*(v - eca) if (g > gmax) { gmax = g } } INITIAL { mhn(v) m = inf[0] h = inf[1] g = gcabar*m*m*m*h ica = g*(v - eca) : initial Ca++ current value gmax = g } DERIVATIVE states { mhn(v) m' = (inf[0] - m)/tau[0] h' = (inf[1] - h)/tau[1] } FUNCTION varss(v (mV), i) { if (i==0) { varss = 1 / (1 + exp((v+60(mV))/(-3(mV)))) :Ca activation } else if (i==1) { varss = 1/ (1 + exp((v+62(mV))/(1(mV)))) :Ca inactivation } } FUNCTION vartau(v (mV), i) (ms) { if (i==0) { vartau = 100 : activation variable time constant } else if (i==1) { vartau = 5 : inactivation variable time constant } } PROCEDURE mhn(v (mV)) {LOCAL a, b :rest = -70 TABLE inf, tau DEPEND celsius FROM -100 TO 100 WITH 200 FROM i=0 TO 1 { tau[i] = vartau(v,i) inf[i] = varss(v,i) } }