Rod photoreceptor (Barnes and Hille 1989, Publio et al. 2006, Kourennyi and Liu et al. 2004)

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Accession:95870
This a conductance-based model of a rod photoreceptor cell based on other modeling works (Barnes and Hille 1989 and Publio et al. 2006 and Kourennyi and Liu et al. 2004 ). In this model four types of ionic channels identified in the inner segment of the rod: nonselective cation channel (h), delayed rectifying potassium channel (Kv), noninactivating potassium channel (Kx) and calcium channel (Ca) was used. The model accurately reproduces the rod response when stimulated with a simulated photocurrent signal. We can show the effect of nonselective cation channel. The absence of this channel cause increasing the peak amplitude and the time to reach the peak of voltage response and absence of transient mode in this response.
References:
1 . Barnes S, Hille B (1989) Ionic channels of the inner segment of tiger salamander cone photoreceptors. J Gen Physiol 94:719-43 [PubMed]
2 . Kourennyi DE, Liu XD, Hart J, Mahmud F, Baldridge WH, Barnes S (2004) Reciprocal modulation of calcium dynamics at rod and cone photoreceptor synapses by nitric oxide. J Neurophysiol 92:477-83 [PubMed]
3 . 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]
4 . Publio R, Oliveira RF, Roque AC (2006) A realistic model of rod photoreceptor for use in a retina network model Neurocomputing 69:1020-1024
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 Cl,Ca; I K,Ca; I Calcium; I Potassium;
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Ion Channel Kinetics; Calcium dynamics;
Implementer(s): Shahali, Mahboubeh [shahali222 at yahoo.com];
Search NeuronDB for information about:  Retina photoreceptor cone GLU cell; I Cl,Ca; I K,Ca; I Calcium; I Potassium;
: Photoreceptor Kx h Ca channel

NEURON 
{
	SUFFIX CPR
	
	USEION Ca WRITE iCa VALENCE 2
	USEION Cl WRITE iCl  VALENCE 1
	USEION Kca WRITE iKca VALENCE 1
	
	NONSPECIFIC_CURRENT  iCGMP
	
	RANGE gCabar, gCa, eCa, SCa, VhalfCa, aoCa
	
             RANGE gClbar,gCl, eCl, SCl
             RANGE gKcabar,gKca, eKca
	
	
	RANGE gCGMP, eCGMP
	
	:temporal parameters
	RANGE FactorCaI
	RANGE mCl, Cas
	
	
	

}

UNITS
{
	(mA) = (milliamp)
	(mV) = (millivolt)
	(mS) = (millimho)
	(mol)= (1)
	(M)  = (mol/liter)
	(uM) = (micro M)
}

PARAMETER
{
       
       : Calcium channel 
       gCabar = 4.9 (mS/cm2) <0,1e9>
       eCa =  40 (mV)
       aoCa = 0.0031  (/ms)
       VhalfCa=-16.6 (mV)
       SCa =5.7      (mV)   
   
       
        
       : Cl channel	
       eCl= -45  (mV)
       gClbar = 6.5 (mS/cm2) <0,1e9>
       SCl = 0.09   (uM)                                                     
       Clh = 0.37 (uM)
       FactorCaI = 0.5    
 
       :Ca-dependent K current
       eKca=-80 (mV)
       gKcabar = 0.5 (mS/cm2) 
 
      	
       : cGMP gated channel	
        gCGMP= 0   (mS/cm2)
	:1.8   (mS/cm2)
        eCGMP=0.8 (mV)
        

}

STATE
{

	nCa
	mKca
	
}

ASSIGNED
{
	v (mV)
	
	iCa (mA/cm2)
             iCl  (mA/cm2)
             iCGMP (mA/cm2) 
             iKca (mA/cm2) 
              
           
           :Ca-dependent potassium channel, Kca
	infmKca
	taumKca  (ms)
	
	infCa
	tauCa  (ms) 
	
	Cas  (uM)
	mCl
	: the paremeter for activation
	
	mKca1
	
	gKca (mho/cm2)
	
	gCa (mho/cm2)
             gCl (mho/cm2)

}

INITIAL
{
	rate(v)
	nCa = infCa
	mKca= infmKca
}




BREAKPOINT
{
	SOLVE states METHOD cnexp
	gCa = (0.001)*gCabar*nCa
	iCa = gCa*(v - eCa)
	
	UNITSOFF
	:if (iCa >= 0) 
	:{
	:	Cas =0
	:}
	:if (iCa < 0) 
	:{
		Cas =-0.2+FactorCaI * (-iCa) * 1 *  0.5         /(1.6e-19)/  (6.023e23) * 1e-6         *1e14    
	:                  mA/cm2 * ms-> n coul/cm2  ->n e /cm2-> nmol/cm2  -> mol /cm2     scale factor
	: all the calculation without consideration of volume
         :    }
                
	
	
	mCl = 1/(1+ exp ( (Clh - Cas)/ SCl  ) ) 
	gCl = (0.001)* gClbar * mCl
	iCl = gCl*(v-eCl)   
	
	mKca1=Cas/(Cas+0.3)
	gKca=(0.001)*gKcabar*mKca*mKca*mKca1
	iKca=gKca*(v-eKca) 
	
	UNITSON
	
	  
	iCGMP = (0.001)*gCGMP*(v-eCGMP)
	
	
	: the current is in the unit of mA/cm2
	
	
}

DERIVATIVE states
{
	rate(v)
	nCa' = (infCa - nCa)/tauCa
	mKca'= (infmKca - mKca ) /taumKca

}


UNITSOFF


FUNCTION alphamKca(v(mV)) (/ms)
{ 
	alphamKca = (0.001)*15*(80-v)/ ( exp( (80-v)/40 ) -1)
	:alter from orginal settings where it is in the unit of 1/s
}

FUNCTION  betamKca (v(mV)) (/ms)
{
	
	betamKca = (0.001)*20*exp (-v/35)
}



UNITSON


FUNCTION alphaCa(v(mV))(/ms)
{ 
	alphaCa = aoCa*exp( (v - VhalfCa)/(2*SCa)   )
}

FUNCTION betaCa(v(mV))(/ms)
{ 
	betaCa = aoCa*exp( - ( v-VhalfCa)/(2*SCa) )
}


PROCEDURE rate(v (mV))
{
        LOCAL a, b

	
	
	a = alphamKca(v)
	b = betamKca(v)
	taumKca = 1/(a + b)
	infmKca = a/(a + b)
	
	
	
	a = alphaCa(v)
	b = betaCa(v)
	tauCa = 1/(a + b)
	infCa = a/(a + b)

}


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