Model of SK current`s influence on precision in Globus Pallidus Neurons (Deister et al. 2009)

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Accession:122329
" ... In numerical simulations, the availability of both Na+ and A-type K+ channels during autonomous firing were reduced when SK channels were removed, and a nearly equal reduction in Na+ and K+ subthreshold-activated ion channel availability produced a large decrease in the neuron's slope conductance near threshold. This change made the neuron more sensitive to intrinsically generated noise. In vivo, this change would also enhance the sensitivity of GP (Globus Pallidus) neurons to small synaptic inputs."
Reference:
1 . Deister CA, Chan CS, Surmeier DJ, Wilson CJ (2009) Calcium-activated SK channels influence voltage-gated ion channels to determine the precision of firing in globus pallidus neurons. J Neurosci 29:8452-61 [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:
Cell Type(s): Globus pallidus neuron;
Channel(s): I Na,p; I Na,t; I A; I K; I K,Ca; I Sodium; I Potassium;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Oscillations; Noise Sensitivity;
Implementer(s): Deister, Christopher [chris.deister at utsa.edu];
Search NeuronDB for information about:  I Na,p; I Na,t; I A; I K; I K,Ca; I Sodium; I Potassium;
NEURON {
	SUFFIX hcn12_gp
	NONSPECIFIC_CURRENT i
	RANGE i, ehcn, g, gbar
	GLOBAL a0, b0, ah, bh, ac, bc, aa0, ba0
	GLOBAL aa0, ba0, aah, bah, aac, bac
	GLOBAL kon, koff, b, bf, ai, gca, shift
}

UNITS {
	(mV)	= (millivolt)
	(molar)	= (1/liter)
	(mM)	= (millimolar)
	(mA)	= (milliamp)
	(S)	= (siemens)
}

PARAMETER {
	gbar    = 1		(S/cm2)
	ehcn    = -20		(mV)
	a0      = .006		(/ms)		: parameters for alpha and beta
	b0      = .0008		(/ms)
	ah      = -96		(mV)
	bh      = -51.7		(mV)
	ac      = -.155		(/mV)
	bc      = .144		(/mV)
	aa0     = .0006		(/ms)		: parameters for alphaa and betaa
	ba0     = .004		(/ms)
	aah     = -94.2		(mV)
	bah     = -35.5		(mV)
	aac     = -.075		(/mV)
	bac     = .144		(/mV)
	kon     = 30		(/mM-ms)	: cyclic AMP binding parameters
	koff    = 4.5e-05	(/ms)
	b       = 80
	bf      = 8.94
	ai	= 1		(mM)		: concentration cyclic AMP
	gca     = 1				: relative conductance of the bound state
	shift   = 5		(mV)		: shift in voltage dependence
	q10v    = 4				: q10 value from Magee 1998
	q10a    = 1.5				: estimated q10 for the cAMP binding reaction
	celsius			(degC)
}

ASSIGNED {
	v	(mV)
	g	(S/cm2)
	i	(mA/cm2)
	alpha	(/ms)
	beta    (/ms)
	alphaa	(/ms)
	betaa	(/ms)
}

STATE {
	c
	cac
	o
	cao
}

INITIAL {
    SOLVE kin STEADYSTATE sparse
}

BREAKPOINT {
	SOLVE kin METHOD sparse
	g = gbar*(o + cao*gca)
	i = g*(v-ehcn)
}

KINETIC kin {
	LOCAL qa
	qa = q10a^((celsius-22 (degC))/10 (degC))
	rates(v)
	~ c <-> o       (alpha, beta)
	~ c <-> cac     (kon*qa*ai/bf,koff*qa*b/bf)
	~ o <-> cao     (kon*qa*ai, koff*qa)
	~ cac <-> cao   (alphaa, betaa)
	CONSERVE c + cac + o + cao = 1
}

PROCEDURE rates(v(mV)) {
	LOCAL qv
	qv = q10v^((celsius-22 (degC))/10 (degC))
	if (v > -200) {
		alpha = a0*qv / (1 + exp(-(v-ah-shift)*ac))
		beta = b0*qv / (1 + exp(-(v-bh-shift)*bc))
		alphaa = aa0*qv / (1 + exp(-(v-aah-shift)*aac))
		betaa = ba0*qv / (1 + exp(-(v-bah-shift)*bac))
	} else {
		alpha = a0*qv / (1 + exp(-((-200)-ah-shift)*ac))
		beta = b0*qv / (1 + exp(-((-200)-bh-shift)*bc))
		alphaa = aa0*qv / (1 + exp(-((-200)-aah-shift)*aac))
		betaa = ba0*qv / (1 + exp(-((-200)-bah-shift)*bac))
	}
}

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