Prediction for the presence of voltage-gated Ca2+ channels in myelinated central axons (Brown 2003)

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"The objective of this current study was to investigate whether voltage gated Ca(2+) channels are present on axons of the adult rat optic nerve (RON). Simulations of axonal excitability using a Hodgkin-Huxley based one-compartment model incorporating I(Na), I(K) and leak currents were used to predict conditions under which the potential contribution of a Ca(2+) current to an evoked action potential could be measured. ... , as predicted by the simulation, reducing the repolarizing effect of I(K) by adding the K(+) channel blocker 4-AP revealed a Ca(2+) component on the repolarizing phase of the action potential that was blocked by the Ca(2+) channel inhibitor nifedipine."
1 . Brown AM (2003) A modeling study predicts the presence of voltage gated Ca2+ channels on myelinated central axons. Comput Methods Programs Biomed 71:25-31 [PubMed]
Model Information (Click on a link to find other models with that property)
Model Type: Axon;
Brain Region(s)/Organism:
Cell Type(s):
Channel(s): I Na,t; I K; I Calcium;
Gap Junctions:
Simulation Environment: XPP;
Model Concept(s): Simplified Models; Tutorial/Teaching; Axonal Action Potentials;
Implementer(s): Wu, Sheng-Nan [snwu at];
Search NeuronDB for information about:  I Na,t; I K; I Calcium;
# AP-sim-Ca.ode

" Ref: Brown AM (2003) Computer Methods and Programs in Biomedicine 71:25-31.
init v=-71, m=0.000734, h=0.726655, n=0.001932, mca=0.003016
param gnabar=20, gkbar=2.0, gkleak=0.007, gnaleak=0.00265, Cao=1, Cai=50e-6, Pca=0.08
param ena=45, ek=-105, Cm=1, z=2
number rgas=8.315, temp=298, faraday=96480
param ton=3, toff=4, ipulse=40

am = 0.091*(v+38)/(1-exp(-(v+38)/5))
bm = -0.062*(v+38)/(1-EXP((v+38)/5))
ah = 0.016*EXP((-55-v)/15)
bh = 2.07/(EXP((17-v)/21)+1)
an = 0.01*(-45-v)/(EXP((-45-v)/5)-1)
bn = 0.17*EXP((-50-v)/40)
amca = 1.6/(1+EXP(-0.072*(v-5)))
bmca = 0.02*(v-1.31)/(EXP((v-1.31)/5.36)-1)

ina = gnabar*(m*m*m)*h*(v-ena)
ik = gkbar*(n^4)*(v-ek)
ica = ((mca^2)*Pca*2e-3*2*v*(faraday^2)/(rgas*temp*1000))* \
ikleak = gkleak*(v-ek)
inaleak = gnaleak*(v-ena)

dm/dt = am*(1-m) - bm*m
dh/dt = ah*(1-h) - bh*h
dn/dt = an*(1-n) - bn*n
dmca/dt = amca*(1-mca) - bmca*mca
dv/dt = (-ina-ik-ica-ikleak-inaleak+Io)/Cm

aux ina=ina
aux ik=ik
aux ica=ica

#  Numerical and plotting parameters for xpp
@ meth=Euler, dt=0.01, total=20, xlo=0, xhi=20, ylo=-80, yhi=60
@ bounds=100000
@ xp=t, yp=v

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