Sodium currents activate without a delay (Baranauskas and Martina 2006)

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Accession:62673
Hodgkin and Huxley established that sodium currents in the squid giant axons activate after a delay, which is explained by the model of a channel with three identical independent gates that all have to open before the channel can pass current (the HH model). It is assumed that this model can adequately describe the sodium current activation time course in all mammalian central neurons, although there is no experimental evidence to support such a conjecture. We performed high temporal resolution studies of sodium currents gating in three types of central neurons. ... These results can be explained by a model with two closed states and one open state. ... This model captures all major properties of the sodium current activation. In addition, the proposed model reproduces the observed action potential shape more accurately than the traditional HH model. See paper for more and details.
Reference:
1 . Baranauskas G, Martina M (2006) Sodium currents activate without a Hodgkin-and-Huxley-type delay in central mammalian neurons. J Neurosci 26:671-84 [PubMed]
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Model Information (Click on a link to find other models with that property)
Model Type: Channel/Receptor;
Brain Region(s)/Organism:
Cell Type(s): Dentate gyrus granule GLU cell; Hippocampus CA1 pyramidal GLU cell; Neocortex L5/6 pyramidal GLU cell; Neocortex L2/3 pyramidal GLU cell;
Channel(s): I Na,t;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Action Potential Initiation; Ion Channel Kinetics; Action Potentials;
Implementer(s): Baranauskas, Gytis [baranauskas at elet.polimi.it];
Search NeuronDB for information about:  Dentate gyrus granule GLU cell; Hippocampus CA1 pyramidal GLU cell; Neocortex L5/6 pyramidal GLU cell; Neocortex L2/3 pyramidal GLU cell; I Na,t;
// vc_demo.hoc
// demonstrates the six-state Na current model in voltage clamp from
// Baranauskas and Martina 2006 J Neurosci 26(2):671-684

// soma is used as a patch of membrane to insert Na model
create soma
access soma

insert MCna1

Na_extern_MCna1=10
Na_intern_MCna1=34

objref VC
soma VC = new VClamp(0.5)

VC.amp[0]=-76
VC.amp[1]=-116
VC.amp[2]=-36
VC.dur[0]=100
VC.dur[1]=70
VC.dur[2]=70
tstop = 240

objref g1, g2
g1 = new Graph()
g1.exec_menu("Keep Lines")
g2 = new Graph()
g2.exec_menu("Keep Lines")

objref cur, t_vec, x, y
cur = new Vector()   // record the Na current
t_vec = new Vector() // record the time steps

cur.record(&soma.ina_MCna1(0.5))
t_vec.record(&t)

celsius = 12

first_stop = int((VC.dur[0]+VC.dur[1])/dt)
last_stop = tstop/dt

for i=1,8 { 
	init() 
	run() 
	x = t_vec.c(0,first_stop)
	y = cur.c(0,first_stop)
	y.line(g1,x)

	x = t_vec.c(first_stop,last_stop)
	y = cur.c(first_stop,last_stop)
	y.line(g2,x)
	VC.amp[1] += 10
}

g1.exec_menu("View = plot")
g2.exec_menu("View = plot")