IClamp, Delay and HH channel conductance

[shd]

Hi,
I built a very simple model:

Code: Select all

load_file("nrngui.hoc")

create soma
access soma

soma {
  nseg = 1
  diam = 18
  L = 18
  Ra = 123.0
  insert hh
  gnabar_hh = 132
}

// create an electrode in the soma

objectvar stim
soma stim = new IClamp(0.5)

stim.del = 350
stim.dur = 100
stim.amp = 1

tstop = 500

The problem is that when I change gnabar_hh to a high value, there's no delay in the IClamp.
I noticed that the maximum value, which the delay works with, changes when I change the soma diameter and length.
In adittion, changing the potassium conductance doesn't make any difference.

What may cause the problem?

Thanks in advance...

[ted]

The problem is that when I change gnabar_hh to a high value, there's no delay in the IClamp.
. . .
In adittion, changing the potassium conductance doesn't make any difference.

These are inferences that you have drawn. What is the evidence that leads you to these inferences?

[shd]

I ment that the potassium channel conductace (gkbar) doesn't make any difference. (Just to be clear, it does change the voltage but it doesn't cause the delay not to work).
I know it, because I tried to change the value of gkbar on a broad range of values and the delay was still working.

[ted]

What is your evidence that "the delay doesn't work"?

[shd]

The graph, voltage vs. time. I got an action potenthial immediately (0<t<5), when the stimulation need to be in time t=350. or maybe I misunderstood the whole idea?

[ted]

The graph, voltage vs. time. I got an action potenthial immediately

And that is the evidence that the current pulse delivered by the IClamp begins at t=0? You changed a property of the model cell, observed an effect on membrane potential in the model cell, and this means that something in the _IClamp_ has changed? Where is the evidence that the current pulse delivered by the IClamp starts at t = 0?

[shd]

Thank you.

[ted]

Plot or print the current delivered by the IClamp as a function of time and see if changing gnabar_hh has any effect on when the current pulse starts. If you're not sure how to create such a plot, see
Q: How do I plot something other than membrane potential?
in NEURON's FAQ list
http://www.neuron.yale.edu/neuron/faq/general-questions