Computer simulations of neuron-glia interactions mediated by ion flux (Somjen et al. 2008)

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Accession:113446
"... To examine the effect of glial K+ uptake, we used a model neuron equipped with Na+, K+, Ca2+ and Cl− conductances, ion pumps and ion exchangers, surrounded by interstitial space and glia. The glial membrane was either “passive”, incorporating only leak channels and an ion exchange pump, or it had rectifying K+ channels. We computed ion fluxes, concentration changes and osmotic volume changes. ... We conclude that voltage gated K+ currents can boost the effectiveness of the glial “potassium buffer” and that this buffer function is important even at moderate or low levels of excitation, but especially so in pathological states."
Reference:
1 . Somjen GG, Kager H, Wadman WJ (2008) Computer simulations of neuron-glia interactions mediated by ion flux. J Comput Neurosci 25:349-65 [PubMed]
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Model Information (Click on a link to find other models with that property)
Model Type: Neuron or other electrically excitable cell; Electrogenic pump; Glia;
Brain Region(s)/Organism:
Cell Type(s): Astrocyte;
Channel(s): I Na,p; I Na,t; I T low threshold; I A; I K; I K,Ca; Na/Ca exchanger; Na/K pump;
Gap Junctions:
Receptor(s): NMDA;
Gene(s):
Transmitter(s): Ions;
Simulation Environment: NEURON;
Model Concept(s): Epilepsy; Calcium dynamics; Sodium pump;
Implementer(s):
Search NeuronDB for information about:  NMDA; I Na,p; I Na,t; I T low threshold; I A; I K; I K,Ca; Na/Ca exchanger; Na/K pump; Ions;
TITLE transient and low threshold calcium current (T-current)

COMMENT
        *********************************************
        reference:  	Huguenard & McCormick (1992) 
			J.Neurophysiology 68(4), 1373-1383
        found in:       thalamic relay neurons
        *********************************************
	Assembled for MyFirstNEURON by Arthur Houweling
ENDCOMMENT

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

NEURON {
	SUFFIX cat
	USEION ca READ cai, cao WRITE ica VALENCE 2
        RANGE gcatbar, ica
        GLOBAL shiftm, shifth, tauh
}

UNITS {
	(mA)	= (milliamp)
	(mV)	= (millivolt)
	(mM)	= (milli/liter)
        FARADAY = 96480 (coul)
        R       = 8.314 (volt-coul/degC)
}

PARAMETER {
	celsius		(degC)
	gcatbar= 0.0001	(cm/s)	
	shiftm = 20 (mV)
	shifth = 20 (mV)
	tauh = 40 (ms)
}

STATE {
	m h
}

ASSIGNED {
	ica
	v
	cai	(mM)
	cao	(mM)
	tadjm
	tadjh
}

BREAKPOINT { 
	SOLVE state METHOD cnexp
	ica = gcatbar * m*m*h * ghk(v,cai,cao,2)
}

DERIVATIVE state {
	m'= (m_inf(v)-m) / tau_m(v)
	h'= (h_inf(v)-h) / tauh
}


INITIAL {
	tadjm= 3.55^((celsius-23.5)/10)
	tadjh= 2.8^((celsius-23.5)/10)
	m = m_inf(v)
	h = h_inf(v)
}

FUNCTION ghk( v(mV), ci(mM), co(mM), z)  (millicoul/cm3) { LOCAL e, w
        w = v * (.001) * z*FARADAY / (R*(celsius+273.16))
        if (fabs(w)>1e-4) 
          { e = w / (exp(w)-1) }
        else : denominator is small -> Taylor series
          { e = 1-w/2 }
        ghk = - (.001) * z*FARADAY * (co-ci*exp(w)) * e
}

FUNCTION tau_m(v) {
	tau_m = (1/(exp((v-shiftm+131.6)/-16.7)+exp((v-shiftm+16.8)/18.2)) + 0.612) / tadjm 
}


FUNCTION m_inf(v) {
	m_inf = 1 / (1+exp((v-shiftm+60.5)/-6.2))
}

FUNCTION h_inf(v) {
	h_inf = 1 / (1+exp((v-shifth+84)/4.03)) 
}