Hi,
Does anyone know how to measure membrane capacitance (hence membrane area) in cell-attached mode or outside/inside-out patches for the area of the patch in the pipette? I came across papers where they derived ion channel conductance density from cell-attached or outside-out recordings. I assume that they needed the membrane area to do this calculation but unsure how you can get membrane capacitance in these setups. I'm only familiar with whole-cell patch clamp recordings.
Thanks!
look at the apendix 1 on this paper. J Neurosci Methods. 2006 June 30; 154(1-2): 1–18.
Cell-attached voltage-clamp and current-clamp recording and stimulation techniques in brain slices
Katherine L. Perkins
Hi! I don't think that a capacitance of a membrane can be found in these mdes, because what you measure as !fast capacitance" is more capacitance of a pipette tip, than of a membrane.
Instead, you can estimate the area from your pipette inner diameter. In cell-attach mode you can more or less safely take it as a flat and have Area=Pi*R^2. Geometry of excised patch seems to be unknown, it may be flat. but may be hemisphere. For rough estimate I would take a "flat" model; anyway error will not be larger than generally when the surface is deduced from capacitance.
Well, this is a complex unresolved issue. As suggested you can estimate the area form your pipette diameter, you may also use the pipette impedance (see Sakmann and Neher in the famous book) or use the apparent diameter of the "bleb" formed by the patch. However, none of them would give you an accurate measurement. I would say that your estimation of the capacitance would be between 50-150 % of the actual value.
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