Hi everyone,
I am performing whole cell current clamp in CA1 hippocampal neurons from slices. I wanted to know what would be the best way to calculate the input resistance of the neurons from the IV curve. Most papers mention using cutom Matlab codes. However I only have the pclamp and clampfit software. Could you guys let me know how to measure it in Clampfit or share a Matlab code for it. Any advice would be most useful.
Thanks!
To measure resistance, one simply use Ohm's law. Under voltage clamp condition, one small voltage step with no elicitation of voltage-gated ion current was applied and measure current amplitude, Then, deltaV divided by current amplitude would yield resistance. If voltage-clamp condition was recorded in whole-cell mode, then the resistance would be commonly expected to whole-cell input resistance.
To measure resistance, one simply use Ohm's law. Under voltage clamp condition, one small voltage step with no elicitation of voltage-gated ion current was applied and measure current amplitude, Then, deltaV divided by current amplitude would yield resistance. If voltage-clamp condition was recorded in whole-cell mode, then the resistance would be commonly expected to whole-cell input resistance.
In complement of what Sheng-Nan answered:
As you are using Clampfit, the software can do it automatically. Select the channel you want the Input Resistance be measured from, put cursors 1-2 on the baseline and cursors 3-4 in your voltage step. Go to Analyze>Resistance..., select your type of experiment (VClamp or CClamp) and the Command channel where the voltage step was applied. It will calculate the resistance for all the sweeps selected, which is really convenient for systematic analysis.
Thanks a lot for your response Sheng-Nan and Sylvain!
Sylvain, I used the method you mentioned in clampfit, however I wasn't sure what the conversion factor you select after selecting current-clamp as experiment type?
Perhaps you may measure input resistance "off-line" since you want to calculate based on the I-V curve. Simply, you picked up several points around Ek and calculate the slope from I-V curve. The input resistance (the reverse of slope value, deltaV/I) can be taken.
The conversion factor is explained in the software, according to your gain (pA / mV for example). If you have a doubt, calculate it yourself for some traces. As Sheng-Nan explained, it is only Ohm's Law: R=U/I.
You may first use Microsoft Excel to calculate the real resistance and then to set the conversion factor appropriately.
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