### 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

Please help me in figuring this out. Thanks!

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}
}
```