COMMENT
caquant.mod
based on mhw.mod, which measures peak depol and calculates spike half width
from the times at which v crosses a (depolarized) threshold.
caquant measures these:
iinit ica at t==0, in mA/cm2
imax most negative (i.e. largest inward) ica, in mA/cm2
timax time at which the most negative ica occurs
hwi half width of the first ica transient that occurs in a simulation
and has most negative value (i.e. dips below) < imax + irest
cinit cai at t==0
cmax largest cai
tcmax time at which the largest cai occurs
caquant also calculates these values:
qapprox = -area*(imax-iinit)*hwi
approximate "extra" charge that enters during the ica transient
(assumes waveform is more or less triangular)
("extra" charge means the difference between the amount that enters
during the ica transient and the amount that would have entered
if the transient hadn't happened)
cmaxp predicted cmax calculated as cinit - svr*(imax-iinit)*hwi/2/FARADAY
where svr is a RANGE variable (a PARAMETER declared to be RANGE)
equal to the surface/volume ratio. svr must be specified by the
user during setup, because it depends on the geometry assumed by
the accumulation mechanism that READs ica and WRITEs cai.
caquant operates in two modes, which are controlled by the PARAMETER (a global)
called mode.
When mode is 1, caquant determines the following in the course of a simulation:
iinit, imax, timax, cinit, cmax, and tcmax
When mode is 2, it does the following in the course of a simulation:
1. uses the values of iinit and imax to set the threshold that it monitors
in order to determine hwi
2. uses the values of hwi, iinit, and imax to calculate qapprox,
and
3. uses the values of cinit, svr, imax, iinit, and hwi to calculate cmaxp.
USAGE EXAMPLE
/*
Run two simulations, first time with parameter mode_caquant = 1
and second time with mode_caquant = 2
At end of first run,
this will equal this
iinit ica at t==0, in mA/cm2
imax most negative (i.e. largest inward) ica, in mA/cm2
timax time at which the most negative ica occurs
cinit cai at t==0
cmax largest cai
tcmax time at which the largest cai occurs
At end of second run,
this will equal this
t0i and t1i the times at which ica crosses the "threshold" iinit+imax/2
hwi half width of the first ica transient
qapprox approximate extra charge that enters during the ica transient
cmaxp predicted cmax
*/
forall {
insert caquant
for (x, 0) svr_caquant(x) = some function that specifies the surface/volume ratio
of the current segment
}
mode_caquant = 1
run()
mode_mhw = 2
run()
hwi will be -1 if there is no max, or if simulation ends before ica crosses
the automatically-set threshold twice
Be cautious when using with adaptive integration--if the integrator uses long dt,
t0i or t1i may be missed by a wide margin.
ENDCOMMENT
NEURON {
SUFFIX caquant
USEION ca READ ica, cai
: mode values--
: 1 measure imax, 2 calc ihalf and measure halfwidth
GLOBAL mode
RANGE iinit, imax, timax
RANGE ihalf, t0i, t1i, hwi
RANGE cinit, cmax, tcmax
RANGE svr : local surface/volume ratio
RANGE qapprox, cmaxp
RANGE vinit, vmax, tvmax
RANGE vhalf, t0v, t1v, hwv
RANGE vxt
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(mM) = (milli/liter)
F = (faraday) (coulombs)
}
PARAMETER {
: mode values--
: 1 measure imax, 2 calc ihalf and measure halfwidth
mode = 1 (1) : default is measure imax
}
ASSIGNED {
ica (mA/cm2)
iinit (mA/cm2) : initial ica
imax (mA/cm2) : max ica during previous run
timax (ms) : time at which imax occurred
ihalf (mA/cm2) : (iinit + imax)/2
t0i (ms) : time in rising phase of cai transient when cai first < ihalf
t1i (ms) : time in falling phase of cai when cai first > ihalf
hwi (ms) : t1i-t0i
findwhichi (1) : 0 to find t0i, 1 to find t1i, 2 to find neither
cai (mM)
cinit (mM) : initial cai
cmax (mM) : max cai during previous run
tcmax (ms) : time at which imax occurred
svr (/micron) : surface/volume ratio, which depends on the ca accumulation mechanism
: for cacum.mod it is depth_cacum
area (micron2) : segment surface area
qapprox (picocoulomb)
cmaxp (mM)
v (mV)
vinit (mV) : initial v
vmax (mV) : max v during previous run
tvmax (ms) : time at which vmax occurred
vhalf (mV) : (vinit + vmax)/2
t0v (ms) : time in rising phase of v transient when v first > vhalf
t1v (ms) : time in falling phase of v when v first < vhalf
hwv (ms) : t1v-t0v
findwhichv (1) : 0 to find t0v, 1 to find t1v, 2 to find neither
vxt (ms mV) : (vmax - vinit)*hwv
}
INITIAL {
if (mode==1) { : measure peak ica
: printf("Finding imax\n")
iinit = ica
: printf("iinit is %g\n", iinit)
imax = ica
timax = t
ihalf = ica
t0i = -1 (ms) : nonsense values for t0i, t1i, hwi
t1i = -1 (ms)
hwi = -1 (ms)
cinit = cai
cmax = cai
tcmax = t
vinit = v
vmax = v
tvmax = t
vhalf = v
t0v = -1 (ms) : nonsense values for t0v, t1v, hwv
t1v = -1 (ms)
hwv = -1 (ms)
} else if (mode==2) { : calc ihalf from iinit and imax in order to determine halfwidth
: printf("Determining ica transient's halfwidth\n")
ihalf = (iinit + imax)/2
: printf("iinit is %g and ihalf is %g\n", iinit, ihalf)
findwhichi = 0 : 0 to find t0i, 1 to find t1i
vhalf = (vinit + vmax)/2
findwhichv = 0 : 0 to find t0v, 1 to find t1v
}
}
: find ica threshold crossings
PROCEDURE findix() {
if (findwhichi==0) {
if (ica < ihalf) {
t0i = t
findwhichi = 1
}
} else if (findwhichi==1) {
if (ica > ihalf) {
t1i = t
hwi = t1i-t0i
findwhichi = 2 : stop looking already
}
}
}
: find v threshold crossings
PROCEDURE findvx() {
if (findwhichv == 0) {
if (v > vhalf) {
t0v = t
findwhichv = 1
}
} else if (findwhichv == 1) {
if (v < vhalf) {
t1v = t
hwv = t1v-t0v
findwhichv = 2 : stop looking already
}
}
}
COMMENT
: steady state m from car mechanism
FUNCTION minf(V (mV))(1) {
minf = 1 / (1 + exp((v+14(mV))/(-6.7 (mV))))
}
ENDCOMMENT
: BREAKPOINT {
: a mechanism that calculate something on every time step
: needs a BREAKPOINT block--even if only an empty one--
: or else it will be treated as an ARTIFICIAL_CELL
BREAKPOINT { }
: AFTER SOLVE { : should work as well, executed half as many times
BEFORE STEP { : should work even with cvode
if (mode==1) { : measure peak ica, cai, v, and pcar
if (icacmax) {
cmax = cai
tcmax = t
}
if (v>vmax) {
vmax = v
tvmax = t
}
} else if (mode==2) {
findix()
qapprox = -(0.01)*area*(imax-iinit)*hwi
cmaxp = cinit - (10000)*svr*(imax-iinit)*hwi/2/F
findvx()
vxt = (vmax - vinit)*hwv
}
}