TITLE Hyperpolarization-activated cation current
: Implemented in Rubin and Cleland (2006) J Neurophysiology
: Adapted from Saraga et al (2003) J. Physiology

UNITS {
        (mA) = (milliamp)
        (mV) = (millivolt)
}
 
NEURON {
        SUFFIX Ih
        USEION h READ eh WRITE ih VALENCE 1
        RANGE gkhbar,ih, i
        GLOBAL rinf, rexp, tau_r
}
 
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
 
PARAMETER {
        v (mV)
        p = 5 (degC)
        dt (ms)
        gkhbar = 0.00 (mho/cm2)			
        eh = -32.9 (mV)
}
 
STATE {
        r
}
 
ASSIGNED {
        ih (mA/cm2)
		i  (mA/cm2)
	rinf rexp
	tau_r
}
 
BREAKPOINT {
        SOLVE deriv METHOD derivimplicit
        ih = gkhbar*r*(v - eh)
		i = ih
}
 
INITIAL {
	rates(v)
	r = rinf
}

DERIVATIVE deriv { :Computes state variable h at current v and dt.
	rates(v)
	r' = (rinf - r)/tau_r
}

PROCEDURE rates(v) {  :Computes rate and other constants at current v.
                      :Call once from HOC to initialize inf at resting v.
        TABLE rinf, rexp, tau_r DEPEND dt, p FROM -200
TO 100 WITH 300

	::::::::: change started here
	if (v > -55 ) {
	rinf = 0
	} else{
	rinf = 1/(1 + exp((v+84.1)/10.2))
	}
	::::::::: and ended here
	
	: rinf = 1/(1 + exp((v+84.1)/10.2))
	rexp = 1 - exp(-dt/(tau_r))
	tau_r = 100 + 1/(exp(-17.9-0.116*v)+exp(-1.84+0.09*v))
}
 
UNITSON