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 Low threshold calcium current
:
:   Ca++ current responsible for low threshold spikes (LTS)
:
:   Written by Alain Destexhe, Salk Institute, Sept 18, 1992
:   Modified by Geir Halnes, Norwegian University of Life Sciences, June 2011:
:
:     - Kinetics adapted to LGN interneuron data from Broicher et al.: Mol Cell Neurosci 36: 132-145, 2007.
:         using Q10 values of 3 and 1.5 for activation/inactivation.
:     - Activation variable shifted 8mV to account for dLGN interneuron data in Halnes et al. 2011


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

NEURON {
	SUFFIX it2
	USEION Ca READ Cai, Cao WRITE iCa VALENCE 2
	RANGE gcabar, g
	GLOBAL m_inf, tau_m, h_inf, tau_h, shift2, sm, sh, phi_m, phi_h, hx, mx, shift1
}

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


PARAMETER {
	v		(mV)
	celsius	= 36	(degC)
	gcabar	= 8.5e-6	(mho/cm2)
      hx      = 1.5
      mx      = 3.0
	Cai	= 5e-5 (mM) : Initial Ca concentration
	Cao	= 2	(mM) : External Ca concentration

: GH, parameters fitted to Broicher et al. 07 - data
	minf1 = 46.2
	hinf1 = 69.7
	taum1 = 5.4
	taum2 = 125.7
	taum3 = -19.7
	taum4 = -0.54
	taum5 = 13
	tauh1 = 21
	tauh2 = 22.2
	tauh3 = 9.1
	tauh4 = 362.9
	tauh5 = 46.9
      sm = 8.7
      sh = 6.4
	shift1 = -8 	(mV) : Halnes et al. 2011
      shift2  = 0    	(mV) : Halnes et al. 2011
}


STATE {
	m h
}

ASSIGNED {
	iCa	(mA/cm2)
	g       (mho/cm2)
	carev	(mV)
	m_inf
	tau_m	(ms)
	h_inf
	tau_h	(ms)
	phi_m
	phi_h
}

BREAKPOINT {
	SOLVE castate METHOD cnexp
	g = gcabar * m*m*h
	iCa = g * ghk(v, Cai, Cao)
}

DERIVATIVE castate {
	evaluate_fct(v)
	m' = (m_inf - m) / tau_m
	h' = (h_inf - h) / tau_h
}

UNITSOFF
INITIAL {
	VERBATIM
	Cai = _ion_Cai;
	Cao = _ion_Cao;
	ENDVERBATIM
:
	phi_m = mx ^ ((celsius-23.5)/10)
	phi_h = hx ^ ((celsius-23.5)/10)

	evaluate_fct(v)
	m = m_inf
	h = h_inf
}

PROCEDURE evaluate_fct(v(mV)) { 
	m_inf = 1.0 / ( 1 + exp(-(v+shift1+minf1)/sm) )
	h_inf = 1.0 / ( 1 + exp((v+shift2+hinf1)/sh) )
	tau_m = (taum1+1.0/(exp((v+shift1+taum2)/(taum3))+exp((v+shift1+taum4)/taum5)))/ phi_m
	tau_h = (tauh1+1/(exp((v+shift2+tauh2)/tauh3)+exp(-(v+shift2+tauh4)/tauh5)))/phi_h
}

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 Cao 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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