The subcellular distribution of T-type Ca2+ channels in LGN interneurons (Allken et al. 2014)

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Accession:156039
" ...To study the relationship between the (Ca2+ channel) T-distribution and several (LGN interneuron) IN response properties, we here run a series of simulations where we vary the T-distribution in a multicompartmental IN model with a realistic morphology. We find that the somatic response to somatic current injection is facilitated by a high T-channel density in the soma-region. Conversely, a high T-channel density in the distal dendritic region is found to facilitate dendritic signalling in both the outward direction (increases the response in distal dendrites to somatic input) and the inward direction (the soma responds stronger to distal synaptic input). ..."
Reference:
1 . Allken V, Chepkoech JL, Einevoll GT, Halnes G (2014) The subcellular distribution of T-type Ca2+ channels in interneurons of the lateral geniculate nucleus. PLoS One 9:e107780 [PubMed]
Model Information (Click on a link to find other models with that property)
Model Type: Neuron or other electrically excitable cell;
Brain Region(s)/Organism: Thalamus;
Cell Type(s): Thalamus lateral geniculate nucleus interneuron;
Channel(s): I L high threshold; I T low threshold; I h; I K,Ca; I CAN; I_AHP;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Dendritic Action Potentials; Active Dendrites; Conductance distributions;
Implementer(s): Allken, Vaneeda [vaneeda at gmail.com];
Search NeuronDB for information about:  I L high threshold; I T low threshold; I h; I K,Ca; I CAN; I_AHP;
TITLE High threshold calcium current
:
:   Ca++ current, L type channels, responsible for calcium spikes
:   Differential equations
:
:   Model of Huguenard & McCormick, J Neurophysiol, 1992
:   Formalism of Goldman-Hodgkin-Katz
:
:   Kinetic functions were fitted from data of hippocampal pyr cells
:   (Kay & Wong, J. Physiol. 392: 603, 1987)
:
:   Written by Alain Destexhe, Salk Institute, Sept 18, 1992
:   Modified by Zhu et al, 1999: Neuroscience 91, 1445-1460 (1999).
:   Modified by Geir Halnes, Norwegian University of Life Sciences, June 2011


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

NEURON {
	SUFFIX ical
	USEION Ca READ Cai, Cao WRITE iCa VALENCE 2
      RANGE pcabar, g
	GLOBAL 	m_inf, taum, sh1, sh2
}


UNITS {
	(mA) = (milliamp)
	(mV) = (millivolt)
	(molar) = (1/liter)
	(mM) = (millimolar)
	FARADAY = (faraday) (coulomb)
	R = (k-mole) (joule/degC)
}


PARAMETER {
	v		(mV)
	celsius	= 36	(degC)
	eCa     = 120		(mV)
	Cai 	= .00005	(mM)	: initial [Ca]i = 50 nM
	Cao 	= 2		(mM)	: [Ca]o = 2 mM
	pcabar	= 9e-4	(mho/cm2)
	sh1 	= -17		 : Modified (-10 in Zhu et al. 99a)
	sh2	= -7		 : Modified (0 in Zhu et al. 99a)
}


STATE {
	m
}

INITIAL {
	tadj = 3 ^ ((celsius-21.0)/10)
	evaluate_fct(v)
	m = m_inf
}


ASSIGNED {
	iCa	(mA/cm2)
	g       (mho/cm2)
	m_inf
	taum	(ms)
      tadj
}

BREAKPOINT { 
	SOLVE states METHOD cnexp
	g = pcabar * m * m
	iCa = g * ghk(v, Cai, Cao)
}

DERIVATIVE states { 
	evaluate_fct(v)
	m' = (m_inf - m) / taum
}


UNITSOFF
PROCEDURE evaluate_fct(v(mV)) {  LOCAL a,b
:  activation kinetics of Kay-Wong were at 20-22 deg. C
:  transformation to 36 deg assuming Q10=3

	a = 1.6 / (1 + exp(-0.072*(v+sh1+5)) )
	b = 0.02 * (v+sh2-1.31) / ( exp((v+sh2-1.31)/5.36) - 1)
	taum = 1.0 / (a + b) / tadj
	m_inf = a / (a + b)
}

FUNCTION ghk(v(mV), ci(mM), co(mM)) (.001 coul/cm3) {
	LOCAL z, eci, eco
	z = (1e-3)*2*FARADAY*v/(R*(celsius+273.15))
	eco = co*efun(z)
	eci = ci*efun(-z)
	:high co charge moves inward
	:negative potential charge moves inward
	ghk = (.001)*2*FARADAY*(eci - eco)
}

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

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