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nax.mod
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nax.mod
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: Eight state kinetic sodium channel gating scheme
: Modified from k3st.mod, chapter 9.9 (example 9.7)
: of the NEURON book
: 12 August 2008, Christoph Schmidt-Hieber
:
: accompanies the publication:
: Schmidt-Hieber C, Bischofberger J. (2010)
: Fast sodium channel gating supports localized and efficient
: axonal action potential initiation.
: J Neurosci 30:10233-42
NEURON {
SUFFIX nax
USEION na READ ena WRITE ina
GLOBAL vShift, vShift_inact, maxrate
RANGE vShift_inact_local
RANGE gna, gbar
RANGE a1_0, a1_1, b1_0, b1_1, a2_0, a2_1
RANGE b2_0, b2_1, a3_0, a3_1, b3_0, b3_1
RANGE bh_0, bh_1, bh_2, ah_0, ah_1, ah_2
}
UNITS { (mV) = (millivolt) }
: initialize parameters
PARAMETER {
: gbar = 33 (millimho/cm2) gbar = 1000 (pS/um2)
a1_0 = 6.264774039489168e+01 (/ms)
a1_1 = 1.160554780103536e-02 (/mV)
b1_0 = 1.936911472259165e-03 (/ms)
b1_1 = 1.377185203515948e-01 (/mV)
a2_0 = 3.478282276988217e+01 (/ms)
a2_1 = 2.995594783341219e-02 (/mV)
b2_0 = 9.575149443481501e-02 (/ms)
b2_1 = 9.281138012170398e-02 (/mV)
a3_0 = 7.669829640279345e+01 (/ms)
a3_1 = 5.374324331056838e-02 (/mV)
b3_0 = 1.248791525464647e+00 (/ms)
b3_1 = 3.115037791363419e-02 (/mV)
bh_0 = 3.573645069880386e+00 (/ms)
bh_1 = 1.933213300303968e-01
bh_2 = 7.496541077890667e-02 (/mV)
ah_0 = 6.882666625638676e+00 (/ms)
ah_1 = 4.654019001523467e+03
ah_2 = 2.958332680760088e-02 (/mV)
vShift = 12 (mV) : shift to the right to account for Donnan potentials
: 12 mV for cclamp, 0 for oo-patch vclamp simulations
vShift_inact = 10 (mV) : global additional shift to the right for inactivation
: 10 mV for cclamp, 0 for oo-patch vclamp simulations
vShift_inact_local = 0 (mV) : additional shift to the right for inactivation, used as local range variable
maxrate = 8.00e+03 (/ms) : limiting value for reaction rates
: See Patlak, 1991
temp = 23 (degC) : original temp q10 = 2.3 : temperature sensitivity q10h = 2.3 : temperature sensitivity celsius (degC)
}
ASSIGNED {
v (mV)
ena (mV)
gna (millimho/cm2)
ina (milliamp/cm2)
a1 (/ms)
b1 (/ms)
a2 (/ms)
b2 (/ms)
a3 (/ms)
b3 (/ms)
ah (/ms)
bh (/ms)
tadj
tadjh
}
STATE { c1 c2 c3 i1 i2 i3 i4 o }
BREAKPOINT {
SOLVE kin METHOD sparse
gna = gbar*o
: ina = g*(v - ena)*(1e-3)
ina = gna*(v - ena)*(1e-4) : define gbar as pS/um2 instead of mllimho/cm2
}
INITIAL { SOLVE kin STEADYSTATE sparse }
KINETIC kin {
rates(v)
~ c1 <-> c2 (a1, b1)
~ c2 <-> c3 (a2, b2)
~ c3 <-> o (a3, b3)
~ i1 <-> i2 (a1, b1)
~ i2 <-> i3 (a2, b2)
~ i3 <-> i4 (a3, b3)
~ i1 <-> c1 (ah, bh)
~ i2 <-> c2 (ah, bh)
~ i3 <-> c3 (ah, bh)
~ i4 <-> o (ah, bh)
CONSERVE c1 + c2 + c3 + i1 + i2 + i3 + i4 + o = 1
}
: FUNCTION_TABLE tau1(v(mV)) (ms)
: FUNCTION_TABLE tau2(v(mV)) (ms)
PROCEDURE rates(v(millivolt)) {
LOCAL vS
vS = v-vShift
tadj = q10^((celsius - temp)/10)
tadjh = q10h^((celsius - temp)/10)
a1 = tadj*a1_0*exp( a1_1*vS)
a1 = a1*maxrate / (a1+maxrate)
b1 = tadj*b1_0*exp(-b1_1*vS)
b1 = b1*maxrate / (b1+maxrate)
: maxrate = tadj*maxrate
a2 = tadj*a2_0*exp( a2_1*vS)
a2 = a2*maxrate / (a2+maxrate)
b2 = tadj*b2_0*exp(-b2_1*vS)
b2 = b2*maxrate / (b2+maxrate)
a3 = tadj*a3_0*exp( a3_1*vS)
a3 = a3*maxrate / (a3+maxrate)
b3 = tadj*b3_0*exp(-b3_1*vS)
b3 = b3*maxrate / (b3+maxrate)
bh = tadjh*bh_0/(1+bh_1*exp(-bh_2*(vS-vShift_inact-vShift_inact_local)))
bh = bh*maxrate / (bh+maxrate)
ah = tadjh*ah_0/(1+ah_1*exp( ah_2*(vS-vShift_inact-vShift_inact_local)))
ah = ah*maxrate / (ah+maxrate)
}