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 l-calcium channel
: l-type calcium channel


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

	FARADAY = 96520 (coul)
	R = 8.3134 (joule/degC)
	KTOMV = .0853 (mV/degC)
}

PARAMETER {
	v (mV)
	celsius 	(degC)
	gcalbar=.003 (mho/cm2)
	ki=.001 (mM)
	cai (mM)
	cao (mM)
        tfa=1
        shiftm=10
        scaletau=.333333
}


NEURON {
	SUFFIX cal
	USEION ca READ cai,cao, eca WRITE ica VALENCE 2
        RANGE gcalbar,cai, ica
        GLOBAL minf ,tau, shiftm, scaletau
}

STATE {
	m
}

ASSIGNED {
	ica	(mA/cm2)
        gcal	(mho/cm2)
        minf
        tau	(ms)
        eca	(mV)
}

INITIAL {
	rate(v)
	m = minf
}

BREAKPOINT {
	SOLVE state METHOD cnexp
	gcal = gcalbar*m*m*h2(cai)
	ica = gcal*(v-eca) :ghk(v,cai,cao)

}

FUNCTION h2(cai(mM)) {
	h2 = ki/(ki+cai)
}


FUNCTION ghk(v(mV), ci(mM), co(mM)) (mV) {
        LOCAL nu,f

        f = KTF(celsius)/2
        nu = v/f
        ghk=-f*(1. - (ci/co)*exp(nu))*efun(nu)
}

FUNCTION KTF(celsius (DegC)) (mV) {
        KTF = ((25./293.15)*(celsius + 273.15))
}


FUNCTION efun(z) {
	if (fabs(z) < 1e-4) {
		efun = 1 - z/2
	}else{
		efun = z/(exp(z) - 1)
	}
}

FUNCTION alp(v(mV)) (1/ms) {
	TABLE DEPEND shiftm, scaletau FROM -150 TO 150 WITH 200
	alp = scaletau*15.69*(-1.0*v-shiftm+81.5)/(exp((-1.0*v-shiftm+81.5)/10.0)-1.0)
}

FUNCTION bet(v(mV)) (1/ms) {
	TABLE DEPEND shiftm, scaletau FROM -150 TO 150 WITH 200
	bet = scaletau*0.29*exp((-v-shiftm)/10.86)
}

DERIVATIVE state {  
        rate(v)
        m' = (minf - m)/tau
}

PROCEDURE rate(v (mV)) { :callable from hoc
        LOCAL a
        a = alp(v)
        tau = 1/(tfa*(a + bet(v)))
        minf = tfa*a*tau
}