NEURON Tutorial #7

Goals: Create the Ih model

Specific aims:

• Use FitTau.ses to get parameters for tau.
• Create MOD file
  • Based on Magee JC (1998), The Journal of Neuroscience
• Generate nrnmech.dll
• Use FitGV.ses to fit GV curve from rate constants.

Downloads:

• FitTau.ses
• FitGV.ses
• Criteria.OPJ
• h.mod
• 07.zip

: Ih based on Magee JC (1998), The Journal of Neuroscience
: Modified by Payne Y. Chang
: Temporature fixed at 33 degC
: External [Na+] = 10 ~ 60 mM
: Reversal potential = -30 mV

TITLE I-h channel from Magee 1998

NEURON {	: Interface definition. Not a variable declaration block.
	SUFFIX h	: Density mechanism
	NONSPECIFIC_CURRENT i
	RANGE gbar	: Location dependent variables
}

UNITS {
	(mA) = (milliamp)
	(mV) = (millivolt)
}

PARAMETER {	: Global variable by defauls
	gbar	= 0.0001	(mho/cm2)
	eh		= -30		(mV)        
	
	:==============================
	: l
	vhalfl	= -80.5	(mV)
	kl		= 6.7	(mV)
	
	:==============================
	: tau
	
	:==============================
	: Alpha for tau
	Aa		= 0.08
	vhalfa	= -107	(mV)
	ka		= 21	(mV)
	
	:==============================
	: Beta for tau
	Ab		= 0.06
	vhalfb	= -54	(mV)
	kb		= -10	(mV)
}

ASSIGNED {	: Range variable by default. Not visible in hoc
	v	(mV)
	i	(mA/cm2)
	linf      
	taul
	gh
}

STATE {
	l
}

INITIAL {
	rate(v)
	l = linf
}

BREAKPOINT {
	SOLVE states METHOD cnexp
	gh = gbar * l
	i = gh * (v - eh)
}

FUNCTION alpha(v(mV)) {
  alpha = Aa/(1 + exp((v - vhalfa)/ka))
}

FUNCTION beta(v(mV)) {
  beta = Ab/(1 + exp((v - vhalfb)/kb))
}

DERIVATIVE states {
	rate(v)
	l' =  (linf - l)/taul
}

PROCEDURE rate(v (mV)) {
	linf = 1/(1 + exp((v-vhalfl)/kl))
	taul = 1/(alpha(v)+beta(v))
}

Fit Tau

Fig GV Curve