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### Making a delay in the activation of an ionic current

Posted: Thu Jan 14, 2016 12:12 pm
Hello!

I am currently doing a model on reproducing the firing of my recordings from interneurons. The main concenpt of this model is to see, how A-type potassium channels creates a delay in the firing, with the appropriate kinetics. In my recordings, the current does not activate until 1-2 ms after the stimulating square-pulse. Because of this, the A-type currents do not contribute to the repolariztaion, or AHP of the spikes. In the mod file (changing kinetic parameters of Lien 2002), I can not declare a delay, therefore, the tranzient potassium current influences the shape of the spike, which is homogenous in my recordings. I need to freely change the conductance density and kinetics of this current, without affecting the spike parameters.

This is my current mod file

Code: Select all

``````TITLE KA
: K-A current for hippocampal interneurons from Lien et al (2002)

NEURON {
SUFFIX ka
USEION k READ ek WRITE ik
RANGE  gbar
GLOBAL minf, hinf, htau, mtau
}

PARAMETER {
gbar = 0.0002   	(mho/cm2)

celsius
ek		(mV)            : must be explicitly def. in hoc
v 		(mV)
a0h=0.17
vhalfh=-105
q10=3
hmin=5
}

UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(pS) = (picosiemens)
(um) = (micron)
}

ASSIGNED {
ik 		(mA/cm2)
minf 		mtau (ms)
hinf	 	htau (ms)
}

STATE { m h}

BREAKPOINT {
SOLVE states METHOD cnexp
ik = gbar*m*h*(v - ek)
}

INITIAL {
trates(v)
m=minf
h=hinf
}

DERIVATIVE states {
trates(v)
m' = (minf-m)/mtau
h' = (hinf-h)/htau
}

PROCEDURE trates(v) {
LOCAL qt
qt=q10^((celsius-23)/10)
minf = (1/(1 + exp(-(v+41.4)/26.6)))^4
mtau=0.5/qt
hinf = 1/(1 + exp((v+78.5)/6))
htau = a0h*(v-vhalfh)/qt
if (htau<hmin/qt) {htau=hmin/qt}
}

``````