Fly lobular plate VS cell (Borst and Haag 1996, et al. 1997, et al. 1999)

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Accession:116956
In a series of papers the authors conducted experiments to develop understanding and models of fly visual system HS, CS, and VS neurons. This model recreates the VS neurons from those papers with enough success to merit approval by Borst although some discrepancies remain (see readme).
References:
1 . Borst A, Haag J (1996) The intrinsic electrophysiological characteristics of fly lobula plate tangential cells: I. Passive membrane properties. J Comput Neurosci 3:313-36 [PubMed]
2 . Haag J, Theunissen F, Borst A (1997) The intrinsic electrophysiological characteristics of fly lobula plate tangential cells: II. Active membrane properties. J Comput Neurosci 4:349-69 [PubMed]
3 . Haag J, Vermeulen A, Borst A (1999) The intrinsic electrophysiological characteristics of fly lobula plate tangential cells: III. Visual response properties. J Comput Neurosci 7:213-34 [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: Drosophila;
Cell Type(s): Fly lobular plate vertical system cell;
Channel(s): I Na,t; I K; I_K,Na;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Reliability; Vision;
Implementer(s): Carnevale, Ted [Ted.Carnevale at Yale.edu]; Torben-Nielsen, Ben [btorbennielsen at gmail.com];
Search NeuronDB for information about:  I Na,t; I K; I_K,Na;
COMMENT
K channel for the fly lobular plate VS cell. Based on the paper:
Haah, theunissen and Borst (1997) "The intrinsic electrophysiological characteristics of fly lobular plate tangential cells: II Active memberane properties".
J. Comp. Neurosc. 4:349-369

Author B. Torben-Nielsen @ TENU/OIST. 2009-01-13 (with help from T. Carnevale)
ENDCOMMENT

NEURON {
	SUFFIX emdk
	USEION k READ ek WRITE ik
	RANGE gk, gbar, i
	RANGE ninf, ntau : would be OK for these to be GLOBAL
	GLOBAL nmidv, nslope, ntaumax, nmidvdn, nslopedn, nmidvup, nslopeup
}


UNITS { : units that are not in the units database should be declared here
  (mV) = (millivolt)
  (mA) = (milliamp)
  (uA) = (microamp)
  (S) = (siemens)
}

PARAMETER {
	: set to the values described in the aforementioned paper
	ek = -20 (mV) : this value will have no effect. set in hoc code
	gbar = 0.001 (S/cm2) 	
	nmidv = 14 (mV)
	nslope = 11 (mV)
	ntaumax = 50.2 (ms)
	nmidvdn = 25 (mV)
	nslopedn = -30 (mV)
	nmidvup = 28 (mV)
	nslopeup = 32 (mV)
}

ASSIGNED {
	: either assigned by the system (e.g., v and i) or by us
	v (mV)
	i 	(mA/cm2)
	ik 	(mA/cm2)
	gk	(S/cm2)
	ninf
	ntau (ms)
}

STATE { n }

INITIAL { 
	rates(v)
	n = ninf
}

BREAKPOINT {
		SOLVE states METHOD cnexp
        gk = gbar*n*n*n*n :n^4
		i = gk * (v - ek) : for convenience, "i" is declared as range so that it can be studied as a seperate current coming from this mechanism.
		ik = i
}

DERIVATIVE states {  
		rates(v)
        n' = (ninf - n)/ntau
}

PROCEDURE rates(v (mV)) 
{
	ninf = 1/ ( 1 + exp( (nmidv-v)/nslope ) )
	ntau = ntaumax / ( exp( (nmidvdn-v)/nslopedn ) + exp( (nmidvup-v)/nslopeup ) )
	: ntau = ntau / ntaumax : EXTRA. ONLY FOR TESTING PURPOSES
}

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