TITLE Ca current through NMDA receptors
: We use this workaround mechanism to calculate the Ca current through the NMDA receptors
: separatly from the non specific ion current through the NMDA receptors in the nmda.mod file
: It contains:
:
: 1.A mechanism to caculate the Ca current through the NMDA receptor
: the Ca current through the NMDA receptor is added to the total Ca current "ica(mA/cm2)"
:
: 2.A balance current "i_canmda(mA/cm2)" (the NONSPECIFIC_CURRENT i in the
: code above) to the Ca current through NMDA receptors (an inward current)
: The balance current is needed because it has already been caculated once as a part of the
: total current through NMDA receptors "i" in the "nmda.mod"
:
: 3.Area (spine head surface area)is declared as a Global variable, and will be used in ampa.mod, nmda.mod, car.mod.
:
: 4.ampa, nmda and R_type current are all sent to this file as current density with the same direction of i_canmda.
: The itotal is just the sum of Inmda Iampa and I R_type
:
: Written by Lei Tian on 04/12/06
NEURON {
SUFFIX canmda
:will be given to the variables in this file as their family name
USEION ca WRITE ica
NONSPECIFIC_CURRENT i
RANGE g, i, mg, inmda, gnmda, iampa, gampa, itotal, irtype, Pca, P, f
GLOBAL Area
:global varible, will be read by other files as a external one
EXTERNAL i2_nmda, g2_nmda, i2_ampa, g2_ampa, irtype_car
:declare the external variables which has been declared as Global ones in nmda.mod, ampa.mod and car.mod
}
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(uS) = (microsiemens)
}
PARAMETER { : parameters that can be entered when function is called in cell-setup
dt (ms)
mg = 1 (mM) :Mg++ concentration
Area = 1.11e-8 (cm2) :spine head area 1.11e-8 (cm2)
k = 1e-06 (mA/nA) :transform the current from in 'nA' to in 'mA'
P (cm/s/uS) :a factor to convert NMDA conductance to permeability by considering the fraction of ca current at -65mV of NMDAr is about 10% normailize it at -65mV
}
ASSIGNED { : parameters needed to solve DE
ica (mA/cm2) :calcium current, which will be add to the total Ca current together with ica in 'car.mod'
v (mV) :spine head membrane potential
i (mA/cm2) :balance current to the ica through NMDA
g (uS) :conductance of nmda(not include the effect of Mg block)
Pca (cm/s) :Ca permeability of NMDA, it's obtained from gnmda by multiplied with P=0.1*gnmda*(v-e_nmda)/GHK at -65mV
inmda (mA/cm2) :equal to -i2_nmda which is the total nmda current's density, the direction is changed to be easier compared with i_canmda in this file.
gnmda (uS) :cunduction of nmda(include the Mg effect), to be easier plot out by just click the 'plot what'button
iampa (mA/cm2):total current of ampa, the direction is changed to be easier compared with i_canmda in this file.
gampa (uS) :cunductance of ampa
itotal (mA/cm2) :total current flow into spinehead (only the aciviated channel current is considered),the direction is chosen the same as i_canmda in this file.
irtype (mA/cm2) :r_type current
f :Ca current fraction in nmda current
}
INITIAL {
P = (1-exp(-65*-0.0755))/(10*Area*14564*(50e-09-(2e-03*exp(-65*-0.0755))))*k :converting conductance to permaebility
}
BREAKPOINT {
g = g2_nmda :[uS]
Pca = P*g :[cm/s]
ica = Pca*14564*v*(50e-09-(2e-03*exp(v*-0.0755)))/(1-exp(v*-0.0755))*1/(1+(exp(0.08(/mV) * -v)*(mg / 0.69))) :ca current density through NMDAr in [mA/cm2]
i = -Pca*14564*v*(50e-09-(2e-03*exp(v*-0.0755)))/(1-exp(v*-0.0755))*1/(1+(exp(0.08(/mV) * -v)*(mg / 0.69))) :balance current density of ca current through nmda
:14564=(z^2*F^2)/(R*T); -0.0755 = -z*F/RT in [1/mV] where z=2,F=96500 in[C/mol], R=8.31 in[J/K*mol], T=308 in[K]
:and everything should be normalizied to [mV], 0.088 and 0.7474 is from our blocking experiment data fitting.
gnmda=g2_nmda*1/(1+(exp(0.08(/mV) * -v)*(mg / 0.69))) :[uS]cunduction of nmda(include the Mg effect), to be easier plot out by just click the 'plot what'button
gampa=g2_ampa :[uS]total current of ampa, the direction is changed to be easier compared with i_canmda in this file
inmda=-i2_nmda :equal to -i2_nmda which is the total nmda current's density, the direction is changed to be easier compared with i_canmda in this file
iampa=-i2_ampa :total current of ampa, the direction is changed to be easier compared with i_canmda in this file.
irtype=irtype_car :R-type current,the direction is chosen to be easier compared with i_canmda in this file.
itotal=i2_nmda+i2_ampa+irtype_car :total current flow into spinehead (only the aciviated channel current is considered),the direction is chosen the same as i_canmda in this file.
f=i/inmda :Ca current fraction in nmda current
}