Attach a very sensitive electrode to a patch of membrane, and measure the current across the membrane keeping the voltage clamped. This process can be used to measure channels as you only get a current if a channel is open. Observations need to be seen using a microscope.
In order to this this first you need to place a pipette tip on the membrane surface and this forms a tight seal over the end of the pipette.
If you pull from here you get inside-out patch clamping, where the internal membrane surface is exposed and you can change things on teh internal surface to see how it is affected.
If you push on the pipette here the whole cell is sealed onto the pipette not just a patch of membrane, allowing you to view the channels in the whole cell.
If you push on the pipette and then pull you get outside-out patch clamping, where the membrane inverts on the pull so the external surface is exposed and you can view things like ligand gated channels.
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