TITLE CaGk
: Calcium activated K channel.
: Modified from Moczydlowski and Latorre (1983) J. Gen. Physiol. 82
UNITS {
(molar) = (1/liter)
}
UNITS {
(mV) = (millivolt)
(mA) = (milliamp)
(mM) = (millimolar)
}
NEURON {
SUFFIX cagk
USEION ca READ cai
USEION k READ ek WRITE ik
RANGE gbar,gkca,ik
GLOBAL oinf, tau
}
UNITS {
FARADAY = (faraday) (kilocoulombs)
R = 8.313424 (joule/degC)
}
PARAMETER {
celsius (degC)
v (mV)
gbar=.01 (mho/cm2) : Maximum Permeability
cai (mM)
ek (mV)
d1 = .84
d2 = 1.
k1 = .48e3 (mM)
k2 = .13e6 (mM)
abar = .28 (/ms)
bbar = .48 (/ms)
st=1 (1)
}
ASSIGNED {
ik (mA/cm2)
oinf
tau (ms)
gkca (mho/cm2)
}
INITIAL {
rate(v,cai)
o=oinf
}
STATE { o } : fraction of open channels
BREAKPOINT {
SOLVE state METHOD cnexp
gkca = gbar*o^st
ik = gkca*(v  ek)
}
DERIVATIVE state { : exact when v held constant; integrates over dt step
rate(v, cai)
o' = (oinf  o)/tau
}
FUNCTION alp(v (mV), c (mM)) (1/ms) { :callable from hoc
alp = c*abar/(c + exp1(k1,d1,v))
}
FUNCTION bet(v (mV), c (mM)) (1/ms) { :callable from hoc
bet = bbar/(1 + c/exp1(k2,d2,v))
}
FUNCTION exp1(k (mM), d, v (mV)) (mM) { :callable from hoc
exp1 = k*exp(2*d*FARADAY*v/R/(273.15 + celsius))
}
PROCEDURE rate(v (mV), c (mM)) { :callable from hoc
LOCAL a
a = alp(v,c)
tau = 1/(a + bet(v, c))
oinf = a*tau
}
