On Jun 19, 11:50 pm, Bill <connelly.b... from gmail.com> wrote:
>> If I've got a standing background noise in a whole-cell voltage clamp
> experiment that I know is mediated by an ion channel (it goes away in
> the presence of all the right drugs and is enhanced by the right drugs
> etc), I am sure I can get some information on the single channel
> conductances that are making this noise.
>> I can find several papers that say things like "Given Variance^2 =
> i^2npo(1-po) we calculated a lorentzian function and found the single
> channel conductance".
>> How do I ACTUALLY do this? Anyone know? I'm sure I could get a graph
> program to fit a lorentzian function to a curve, if I could calculate
> the right curve in the first place, which is a spectral density
> function, which plots A^2/Hz vs Hz.
>> Does anyone have any idea what I'm talking about? (I certainly don't).
> Can anyone offer some rough tips on what I need to do? I have access
> to CED software, MiniAnalysis and John Dempsters WinWCP package.
This analysis basically involves computing the power spectrum of chuck
of data, then fitting that to a Lorentzian function. To take the PS
you use the FFT, which I think that Dempster's software should be able
to do. Sometimes people use tricks to smooth the data and get better
fits, but this is not absolutely essential if you have nice long
stretches of clean data. One trick is to repeat the FFT on multiple
segments, then average the FFTs.
Anyway, try looking at this old paper for an example:
Segal M, Barker JL.
Rat hippocampal neurons in culture: properties of GABA-activated Cl-
J Neurophysiol. 1984 Mar;51(3):500-15.
PMID: 6321695 [PubMed - indexed for MEDLINE]
BTW, usually you want to do this TWICE: once with the channel active,
then once with it blocked. Then you subtract those two PSs from each
other to isolate the spectrum of the channel of interest.