Dear all,
Do anyone know what is the way to calculate how many channels there are in one cell, if I know the total current from the specific chennels in that cell and also a current from just one spesific channel.?
Thanks

Check out this reference which demonstrates how to measure the channel capacity of a neuron, as well as, how to calculate the upper and lower bounds on information transfer based on Information Theory.


Alexander Borst and Frédéric E. Theunissen. Information theory and neural coding. Nature Neuroscience 2, 947 - 957 (1999). doi:10.1038/14731

Abstract
Information theory quantifies how much information a neural response carries about the stimulus. This can be compared to the information transferred in particular models of the stimulus−response function and to maximum possible information transfer. Such comparisons are crucial because they validate assumptions present in any neurophysiological analysis. Here we review information-theory basics before demonstrating its use in neural coding. We show how to use information theory to validate simple stimulus−response models of neural coding of dynamic stimuli. Because these models require specification of spike timing precision, they can reveal which time scales contain information in neural coding. This approach shows that dynamic stimuli can be encoded efficiently by single neurons and that each spike contributes to information transmission. We argue, however, that the data obtained so far do not suggest a temporal code, in which the placement of spikes relative to each other yields additional information.

Hope I'm not oversimplifying this, but it seems the quick calculation would be:

N_channels = total current/current per channel.

Hope I'm not oversimplifying this, but it seems the quick calculation would be:

N_channels = total current/current per channel.

If you are just estimating the number of channels gating the particular whole cell trace you recorded then dividing the whole cell current by the single channel current under the same recording conditions is good enough.

But if you wan to estimate the total number of channels at the plasma membrane, then you also have to take into consideration the open channel probability Po under the conditions you recorded the current and any inactivation or desensitization that may occur.

Forgetting inactivation and desensitization for now, If Po is 50% at the voltage at which you recorded your current, and you calculated 100 channels from your whole cell current and single channel conductance, then there are probably 200 channels that could potentially gate current actually in the plasma membrane.

Even this is a drastic oversimplification, but it may serve Guy's purpose.

Thanks for all the answers.
But isnt all of those calculations to simple. Some how I would think it would be much more complicated.
Even if you take in consideration the Po I think that something else is missing. I am asking it from an electrification's point of view.
Thanks
Guy

Po itself is generally voltage dependent, so if you want to be completely accurate you need to know the Po at the voltage at which you recorded your current.

Are you actually interested in the absolute channels per cell or the change in channel number as a result of a mutation or drug treatment?

If the latter is true you can generally compare the current densities from whole cell recordings (pA/pF) to see if channel number increased or decreased, as this is a good indicator of channel number per unit surface area of plasma membrane.

I had a disscution with another colleague he said that it is possible to do what you are proposing but some how I dont think that it is so simple. Yes he would like to know how many channels per cell there are, in one cell.
Guy