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(2):671-684 [PubMed]
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 cell; Hippocampus CA1 pyramidal cell; Neocortex V1 pyramidal corticothalamic L6 cell; Neocortex V1 pyramidal intratelencephalic L2-5 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 cell; Hippocampus CA1 pyramidal cell; Neocortex V1 pyramidal corticothalamic L6 cell; Neocortex V1 pyramidal intratelencephalic L2-5 cell; I Na,t;
TITLE HH sodium channel
: Hodgkin - Huxley squid sodium channel
: file updated to provide temperature dependence 1/17/2006

NEURON {
	SUFFIX kder_sej
	USEION k READ ek WRITE ik
	RANGE gkdersejbar, ik, gkder

}

UNITS {
	(mA) = (milliamp)
	(mV) = (millivolt)
}

INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}

PARAMETER {
        v (mV)
        dt (ms)
	gkdersejbar=.086 (mho/cm2) <0,1e9>
        ek = -104 (mV)
}

STATE {
	m
}

ASSIGNED {
	ik (mA/cm2)
	minf hinf
	mtau (ms)
        gkder (mho/cm2)
}

INITIAL {
	rate(v)
	m = minf
}

BREAKPOINT {
	SOLVE states METHOD cnexp
	gkder = gkdersejbar*m*m*m*m
        ik = gkder*(v - ek)
}

DERIVATIVE states {
	rate(v)
	m' = (minf - m)/mtau

}

UNITSOFF

FUNCTION malf(v(mV))(/ms){ LOCAL va
	va = v + 20  
	if (fabs(va)<1e-04) {
		malf = -0.02*(-9 + 0.5*va)
	}else{
		malf = 0.02*(v+20)/(1-exp(-(v+20)/9)) 
	}
}

FUNCTION mbet(v(mV))(/ms) { LOCAL vb
	vb = v + 20
	if (fabs(vb)<1e-04) {
		mbet = 0.002*(9+vb*0.5)
	}else{
		mbet = 0.002*(v+20)/(-1+exp((v+20)/9))
	}
}




PROCEDURE rate(v(mV)) {LOCAL q10, msum, ma, mb
	TABLE minf, mtau DEPEND celsius FROM -100 TO 100 WITH 200

        q10 = (2.8)^((celsius - 23)/10)
	ma=malf(v+1) mb=mbet(v+1) 
	msum = ma + mb
        minf = ma/msum
        mtau = 1/(q10*msum)



}

UNITSON

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