TITLE P 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 CaP
USEION ca READ eca WRITE ica
RANGE gcabar, ica, gca, minf, hinf, mexp, hexp
}
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
PARAMETER {
v (mV)
cao = 2.4 (mM) : external ca concentration
cai (mM)
celsius = 37 (degC)
dt (ms)
gcabar = .0045 (mho/cm2)
}
STATE {
m h
}
ASSIGNED {
ica (mA/cm2)
gca (mho/cm2)
eca
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 = 8.5/(1+exp((v-8)/(-12.5)))
beta = 35/(1+exp((v+74)/14.5))
sum = alpha + beta
minf = alpha/sum
mexp = 1 - exp(tinc*sum)
:"h" calcium inactivation system
alpha = 0.0015/(1+exp((v+29)/8))
beta = 0.0055/(1+exp((v+23)/(-8)))
sum = alpha + beta
hinf = alpha/sum
hexp = 1 - exp(tinc*sum)
}
UNITSON