COMMENT
calcium accumulation into a volume of area*depth next to the
membrane with a decay (time constant tau) to resting level
given by the global calcium variable cai0_ca_ion
Modified to include a resting current (irest) and peak value
(cmax)
i is a dummy current needed to force a BREAKPOINT
ENDCOMMENT
NEURON {
SUFFIX cacum
USEION ca READ ica WRITE cai
NONSPECIFIC_CURRENT i
RANGE depth, tau, cai0, cmax
}
UNITS {
(mM) = (milli/liter)
(mA) = (milliamp)
F = (faraday) (coulombs)
}
PARAMETER {
depth = 0.1 (um) : assume volume = area*depth
irest = 0 (mA/cm2) : to be initialized in hoc
tau = 100 (ms)
cai0 = 0(mM) : 50e6 :Requires explicit use in INITIAL
: block for it to take precedence over cai0_ca_ion
: Do not forget to initialize in hoc if different
: from this default.
}
ASSIGNED {
ica (mA/cm2)
cmax
i (mA/cm2)
}
STATE {
cai (mM)
}
INITIAL {
cai = cai0
irest = ica
cmax=cai
}
BREAKPOINT {
SOLVE integrate METHOD derivimplicit
if (cai>cmax) {cmax=cai}
i=0
}
DERIVATIVE integrate {
cai' = (irestica)/depth/F/2 * (1e4) + (cai0  cai)/tau
}
