TITLE Ca Rtype channel with high threshold for activation
: HVA calcium channels are inserted in the spine head
: Activation and inactivation parameters taken from
: Foehring RC, Mermelstein PG, Song W, Ulrich S and Surmeier DJ
: Unique properities of Rtype calcium currents in neucortical and neostriatal neurons
: J Neurophysiol (2000) 84: 2225  2236
:
: written by Lei Tian on 04/11/06
NEURON {
SUFFIX car
USEION ca WRITE ica
RANGE gcabar, m, h, g, p, eca
RANGE inf, fac, tau, k
GLOBAL irtype
EXTERNAL Area_canmda
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
}
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
PARAMETER { : parameters that can be entered when function is called in cellsetup
v (mV)
celsius = 30 (degC)
dt (ms)
gcabar = 0.351 (mho/cm2) : initialized conductance
eca = 10 (mV) : Ca++ reversal potential was choosen to best fit the GHK between 40 and 10 mV
Area (cm2)
k = 1e06 (mA/nA)
}
STATE { m h }
ASSIGNED {
ica (mA/cm2)
inf[2]
fac[2]
tau[2]
irtype
g :R_type channel total conductance
p
}
BREAKPOINT {
SOLVE states
ica = gcabar*m*m*m*h*(v  eca)
irtype= gcabar*m*m*m*h*(v  eca)
g = gcabar*m*m*m*h*Area*1e6 :[uS]
p = m*m*m*h
}
INITIAL {
Area = Area_canmda
m = 0 : initial activation parameter value
h = 0.5 : initial inactivation parameter value
states()
ica = gcabar*m*m*m*h*(v  eca) : initial Ca++ current value
irtype=gcabar*m*m*m*h*(v  eca) : the ca current through R_type channel
g = gcabar*m*m*m*h*Area*1e6 :[uS]
p = m*m*m*h
}
PROCEDURE calcg() {
mhn(v*1(/mV))
m = m + fac[0]*(inf[0]  m)
h = h + fac[1]*(inf[1]  h)
}
PROCEDURE states() { : exact when v held constant
calcg()
VERBATIM
return 0;
ENDVERBATIM
}
FUNCTION varss(v, i) {
if (i==0) {
varss = 1 / (1 + exp((v+14)/(6.7))) : Ca activation
}
else if (i==1) {
varss = 1/ (1 + exp((v+65)/(11.8))) : Ca inactivation
}
}
FUNCTION vartau(v, i) {
if (i==0) {
vartau = 3.6 : activation variable time constant
}
else if (i==1) {
vartau = 200 : inactivation variable time constant
}
}
PROCEDURE mhn(v) {LOCAL a, b :rest = 70
: TABLE inf, fac DEPEND dt, celsius FROM 100 TO 100 WITH 200
FROM i=0 TO 1 {
tau[i] = vartau(v,i)
inf[i] = varss(v,i)
fac[i] = (1  exp(dt/tau[i]))
}
}
