TITLE t-type calcium channel with high threshold for activation : used in somatic and dendritic regions : it calculates I_Ca using channel permeability instead of conductance UNITS { (mA) = (milliamp) (mV) = (millivolt) (molar) = (1/liter) (mM) = (millimolar) FARADAY = (faraday) (coulomb) R = (k-mole) (joule/degC) } PARAMETER { :parameters that can be entered when function is called in cell-setup v (mV) tBase = 23.5 (degC) celsius = 22 (degC) gcatbar = 0 (mho/cm2) : initialized conductance ki = 0.001 (mM) cai = 5.e-5 (mM) : initial internal Ca++ concentration cao = 2 (mM) : initial external Ca++ concentration tfa = 1 : activation time constant scaling factor tfi = 0.68 : inactivation time constant scaling factor eca = 140 : Ca++ reversal potential } NEURON { SUFFIX cat USEION ca READ cai,cao USEION Ca WRITE iCa VALENCE 2 : The T-current does not activate calcium-dependent currents. : The construction with dummy ion Ca prevents the updating of the : internal calcium concentration. RANGE gcatbar, hinf, minf, taum, tauh, iCa, gmax } STATE { m h } : unknown activation and inactivation parameters to be solved in the DEs ASSIGNED { : parameters needed to solve DE iCa (mA/cm2) gcat (mho/cm2) gmax (mho/cm2) minf hinf taum (ms) tauh (ms) } INITIAL { : tadj = 3^((celsius-tBase)/10) : assume Q10 of 3 rates(v) m = minf h = hinf gcat = gcatbar*m*m*h*h2(cai) gmax = gcat } BREAKPOINT { SOLVE states METHOD cnexp gcat = gcatbar*m*m*h*h2(cai) : maximum channel permeability iCa = gcat*ghk(v,cai,cao) : dummy calcium current induced by this channel if (gcat > gmax) { gmax = gcat } } FUNCTION h2(cai(mM)) { h2 = ki/(ki+cai) } FUNCTION ghk(v(mV), ci(mM), co(mM)) (mV) { LOCAL nu,f f = KTF(celsius)/2 nu = v/f ghk=-f*(1. - (ci/co)*exp(nu))*efun(nu) } FUNCTION KTF(celsius (degC)) (mV) { : temperature-dependent adjustment factor KTF = ((25(mV)/293.15(degC))*(celsius + 273.15(degC))) } FUNCTION efun(z) { if (fabs(z) < 1e-4) { efun = 1 - z/2 }else{ efun = z/(exp(z) - 1) } } FUNCTION alph(v(mV)) (/ms) { alph = 1.6e-4(/ms)*exp(-(v+57(mV))/19(mV)) } FUNCTION beth(v(mV)) (/ms) { beth = 1(/ms)/(exp((-v+15(mV))/10(mV))+1.0) } FUNCTION alpm(v(mV)) (/ms) { alpm = 0.1967(/ms)*(-1.0(/mV)*v+19.88)/(exp((-1.0*v+19.88(mV))/10.0(mV))-1.0) } FUNCTION betm(v(mV)) (/ms) { betm = 0.046(/ms)*exp(-v/22.73(mV)) } :if state_cagk is called from hoc, garbage or segmentation violation will :result because range variables won't have correct pointer. This is because : only BREAKPOINT sets up the correct pointers to range variables. DERIVATIVE states { : exact when v held constant; integrates over dt step rates(v) m' = (minf - m)/taum h' = (hinf - h)/tauh } PROCEDURE rates(v (mV)) { :callable from hoc LOCAL a TABLE taum, minf, tauh, hinf FROM -150 TO 150 WITH 300 a = alpm(v) taum = 1/(tfa*(a + betm(v))) : estimation of activation tau minf = a/(a+betm(v)) : estimation of activation steady state a = alph(v) tauh = 1/(tfi*(a + beth(v))) : estimation of inactivation tau hinf = a/(a+beth(v)) : estimation of inactivation steady state }