Simulated light response in rod photoreceptors (Liu and Kourennyi 2004)

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Accession:64228
We developed a complete computer model of the rod, which accurately reproduced the main features of the light response and allowed us to demonstrate that it was suppression of Kx channels that was essential for slowing SLR and increasing excitability of rods. The results reported in this work further establish the importance of Kx channels in rod photoreceptor function.
Reference:
1 . Liu XD, Kourennyi DE (2004) Effects of tetraethylammonium on Kx channels and simulated light response in rod photoreceptors. Ann Biomed Eng 32:1428-42 [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;
Brain Region(s)/Organism:
Cell Type(s): Retina photoreceptor cone GLU cell;
Channel(s): I Chloride; I L high threshold; I K; I h; I K,Ca; I Potassium;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Action Potential Initiation; Oscillations; Action Potentials; Calcium dynamics;
Implementer(s): Kourennyi, Dmitri E [dek at case.edu]; Liu, Xiaodong [xliu22 at jhmi.edu];
Search NeuronDB for information about:  Retina photoreceptor cone GLU cell; I Chloride; I L high threshold; I K; I h; I K,Ca; I Potassium;
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Liu-Kourennyi_2004
readme.txt
Ca.mod *
Cad.mod
Clca.mod
h.mod
IinjLT.mod *
IinjLTDim.mod *
IinjSin.mod
Kca.mod
Kv.mod
Kx.mod *
Leak.mod *
0222AP_BR.ses
0222AP_DIM.ses
0222Kx_BR.ses
0222Kx_DIM.ses
Fig5_IVCompare.ses
Fig9_AP_Patterns.ses
init.hoc
mosinit.hoc *
rod.hoc
                            
TITLE decay of internal calcium concentration
:
: Internal calcium concentration due to calcium currents and pump.
: Differential equations.
:
: Simple model of ATPase pump with 3 kinetic constants (Destexhe 92)
:     Cai + P <-> CaP -> Cao + P  (k1,k2,k3)
: A Michaelis-Menten approximation is assumed, which reduces the complexity
: of the system to 2 parameters: 
:       kt = <tot enzyme concentration> * k3  -> TIME CONSTANT OF THE PUMP
:	kd = k2/k1 (dissociation constant)    -> EQUILIBRIUM CALCIUM VALUE
: The values of these parameters are chosen assuming a high affinity of 
: the pump to calcium and a low transport capacity (cfr. Blaustein, 
: TINS, 11: 438, 1988, and references therein).  
:
: Units checked using "modlunit" -> factor 10000 needed in ca entry
:
: VERSION OF PUMP + DECAY (decay can be viewed as simplified buffering)
:
: All variables are range variables
:
:
: This mechanism was published in:  Destexhe, A. Babloyantz, A. and 
: Sejnowski, TJ.  Ionic mechanisms for intrinsic slow oscillations in
: thalamic relay neurons. Biophys. J. 65: 1538-1552, 1993)
:
: Written by Alain Destexhe, Salk Institute, Nov 12, 1992
:
: This file was modified by Yiota Poirazi (poirazi@LNC.usc.edu) on April 18, 2001 to account for the sharp
: Ca++ spike repolarization observed in: Golding, N. Jung H-Y., Mickus T. and Spruston N
: "Dendritic Calcium Spike Initiation and Repolarization are controlled by distinct potassium channel
: subtypes in CA1 pyramidal neurons". J. of Neuroscience 19(20) 8789-8798, 1999.
:
:  factor 10000 is replaced by 10000/18 needed in ca entry
:  taur --rate of calcium removal-- is replaced by taur*7 (7 times faster) 

: Xiaodong Liu 2003-12-08 Calcium Dynamics for Rod inner segment

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

NEURON {
	SUFFIX Cad
	USEION Ca READ iCa, Cai WRITE Cai,Cao VALENCE 2	
        RANGE Ca, depth, Cainf, taur, entryF
}

UNITS {
	(molar) = (1/liter)			: moles do not appear in units
	(mM)	= (millimolar)
	(um)	= (micron)
	(mA)	= (milliamp)
	(msM)	= (ms mM)
	FARADAY = (faraday) (coulomb)
}


PARAMETER {
	depth	= .1	(um)		: depth of shell
	taur	= 200	(ms)		: rate of calcium removal
	Cainf	= 2e-3  (mM)		: 2uM
	Cai		(mM)
	Cao     = 2     (mM)
	entryF  = 1
}

STATE {
	Ca		(mM) 
}

INITIAL {
	Ca = Cainf
	Cao=2
	
}

ASSIGNED {
	iCa		(mA/cm2)
	drive_channel	(mM/ms)
}
	
BREAKPOINT {
	SOLVE state METHOD derivimplicit
}

DERIVATIVE state { 

	drive_channel =  - (10000) * iCa / (2 * FARADAY * depth)
	if (drive_channel <= 0.) { drive_channel = 0.  }   : cannot pump inward 
         
	:ca' = drive_channel + (cainf-ca)/taur
        :Ca' = drive_channel/18 + (Cainf -Ca)/taur*7
	Ca' = entryF*drive_channel/2 + (Cainf-Ca)/taur
	
        Cai = Ca
	Cao=2 :mM
}