TITLE Persistent sodium current
 
COMMENT
 from "An Active Membrane Model of the Cerebellar Purkinje Cell
        1. Simulation of Current Clamp in Slice"
ENDCOMMENT
 
UNITS {
        (mA) = (milliamp)
        (mV) = (millivolt)
}
 
NEURON {
 	SUFFIX NaP
	USEION na WRITE ina
	RANGE gnabar, gna, minf, ina
}
 
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
 
PARAMETER {
  	v		(mV)
	celsius	= 37	(degC)
	ena	= 45	(mV)
	gnabar	= 0.001 (mho/cm2)
        dt
}
 
STATE {
        m 
}
 
ASSIGNED {
        ina (mA/cm2)
 	minf
        mexp
        gna
}
 
BREAKPOINT {
        SOLVE states
       
        gna = gnabar*m*m*m
        ina = gna*(v - ena)
  
}
 
UNITSOFF
 
INITIAL {
	rates(v)
	m = minf
}

PROCEDURE states() {  :Computes states variable m
        rates(v)      :             at the current v and dt.
        m = m + mexp*(minf-m)

}
 
PROCEDURE rates(v) {  :Computes rate and other constants at current v.
                      :Call once from HOC to initialize inf at resting v.
        LOCAL  q10, tinc, alpha, beta, sum
        TABLE minf, mexp DEPEND dt, celsius FROM -100 TO 100 WITH 200
        q10 = 3^((celsius - 37)/10)
        tinc = -dt * q10
                :"m" sodium activation system
        alpha = 200/(1+exp((v-18)/(-16)))
        beta =  25/(1+exp((v+58)/8))
        sum = alpha + beta
        minf = alpha/sum
        mexp = 1 - exp(tinc*sum)
}
 

 
UNITSON