COMMENT
This file, fast.mod, implements the Fast [Ca2+] sensor from
Liu et al. 1998 (Activity dependent conductances)
Tom M Morse 20070806
Note that the transition rates depend on the Ca current, ica,
rather than on the membrane voltage.
ENDCOMMENT
NEURON {
SUFFIX F
USEION ca READ ica
RANGE F, M, H
}
UNITS {
(mA) = (milliamp)
}
PARAMETER {
G = 10 : p2312 after eqn. 4
tau_M = 0.5 (ms) : p. 2313, table 2
tau_H = 1.5 (ms) : table 2 also
Z_M = 14.2 : table 2 also
Z_H = 9.8 : table 2 also
}
ASSIGNED {
Mbar (1) : Mbar and Hbar play the roles of m_inf, h_inf in
Hbar (1) : standard HH models
ica (mA/cm2)
F (1)
}
STATE { M H }
BREAKPOINT {
SOLVE states METHOD cnexp
F = G * M * M * H : note there is no driving force
}
INITIAL {
: assume that ica has been constant for a long time at startup
rates(ica)
M = Mbar
H = Hbar
}
DERIVATIVE states {
rates(ica)
M' = (Mbar  M)/tau_M
H' = (Hbar  H)/tau_H
}
PROCEDURE rates(ica (mA/cm2)) {
UNITSOFF
Mbar = 1/(1+exp( Z_M + 1e3*ica )) : units mA/cm2 is 1e3*nA/nF when
Hbar = 1/(1+exp( Z_H  1e3*ica )) : specific capacitance= 1 uF/cm2
UNITSON
}
