TITLE sodium leak

COMMENT 

 Sodium leak.  This TTX sensitive sodium current is active
 between spikes and has some voltage dependence (although no
 inactivation that I know of) (Do & Bean 2003).  I based the
 voltage dependence of this channel on the Do & Bean data, but found a
 pure leak had the same effect, so I stuck to the pure leak..

 How the q10 works: There is a q10 for the rates (alpha and beta's)
 called Q10 and a Q10 for the maximum conductance called gmaxQ10.  The
 q10s should have been measured at specific temperatures temp1 and
 temp2 (that are 10degC apart). Ideally, as Q10 is temperature
 dependant, we should know these two temperatures.  We used to
 follow the more formal Arrhenius derived Q10 approach.  The
 temperature at which this channel's kinetics were recorded is tempb
 (base temperature).  What we then need to calculate is the desired
 rate scale for now working at temperature celsius (rate_k).  This was
 given by the empirical Arrhenius equation, using the Q10, but now is 
 using the quick Q10 approximation. 
ENDCOMMENT

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

NEURON {
       SUFFIX NaL
       USEION na READ ena,nai WRITE ina
       RANGE gna,inaL
       GLOBAL activate_Q10,gmaxQ10,gmax_k,temp1,temp2,tempb
}

PARAMETER {
        v (mV)
	gna = 0.81e-5 (mho/cm2)
	inaL = 0.0 (mA/cm2)
	ena
	nai
	celsius

	activate_Q10 = 1
	gmaxQ10 = 1.5
	temp1 = 25.0 (degC)
	temp2 = 35.0 (degC)
	tempb = 23.0 (degC)	
}

ASSIGNED { 
        ina (mA/cm2)
	gmax_k
}

BREAKPOINT {
	   ina	= gna*gmax_k*(v-ena)
	   inaL = ina
}
UNITSOFF

INITIAL {
	LOCAL ktemp,ktempb,ktemp1,ktemp2
	if (activate_Q10>0) {
	  gmax_k = gmaxQ10^((celsius-tempb)/10)
	}else{
	  gmax_k = 1.0
	}
}	
UNITSON