Has anyone tried using their patch clamp amplifier in current clamp mode to make intracellular voltage recording with sharp electrodes? We’re having major difficulty getting gigaseals so pondering alternative approaches.
I recall that decades ago people used sharp electrodes to do voltage clamp, using chopping between voltage measuring mode and current passing mode. I wonder how difficult it would be to repurpose a patch clamp amplifier to do this. My guess is that it would have a terrible time response, due to limited current passing capacity compared to what is needed to pass significant current through a high impedance sharp electrodes.
As far as I know, usual patch clamp amplifiers are not too good for work in current clamp mode.
I think that devices with discontinuous-single-electrode voltage-clamp mode should be better in this regard. Some of this should be still commercially available. If you need current clamp mode only, you can use old-fashioned intracellular amplifiers – which are basically voltage followers (though I’m not sure they are still commercially available). Circuits of intracellular amplifiers are reasonably simple, I’ve made a couple of these several decades ago.
Hi Robert,
A sharp electrode filled with 3M KCl typically has 20-60 megaOhms resistance in bath, depending on the soma size. What is the resistance of your electrodes and also which cells are you trying to record from?
I would recommend to use low resistance ~20 megaOhm electrodes (even a bit lower ~15 mOhm) if your cells are 20-30 micron in diameter. Also do not try to get a gigaseal, just do a directly impail the cell soma with the electrode and then clamp the cell after. I would not waste time trying to form gigaOhm seal, which can easily result in blockage of the tip. Obviously the clamp will be far from perfect, especially if you are recording from cells with processes, however you can control the voltage within the immediate vicinity of the soma.
I have used it in the past in in vivo work as well as in vitro and cultured neurons, for example to evoke action potentials in cells with resting membrane potential below threshold.
For example, check our 1996 in vivo J. Physiology paper-Fig 8C and 9D in particular. Also JNeurophysiology paper on whole-mount pelvic ganglion neurons, Fig 3A-C.
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best wishes,
Refik
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