I'm conducting whole cell patch clamp experiments in acute slices of accessory olfactory bulb (mitral cells) in mice.
I'm achieving a G-ohm seal and going to whole cell configuration without problems, but in almost every cell I get an abrupt drop in resistance (3-8 fold), 3-20 minutes after breaching the membrane. After this happens the recording gets very noisy, and usually I have to drop the cell. I attached an example recording (in VC) during which it happened. It contains a pulse train, but the phenomenon isn't related to stimuli (it also happens "spontaneously").
In some occasions the resistance goes back to it's initial value, just as abruptly as it dropped. This leads me to the conclusion that nothing is actually happening to the cell, but rather to the pipette connection with the membrane.
Other researchers in the lab are using the same setup for WC patch of (much larger) cerebellar Purkinje cells, and they don't experience the full extent of the problem as I do.
Needless to say, this presents a big obstacle for my research, and I already tried a lot of proposed solutions -
* Changing pipette width (usually I use ~8MOhm, tried higher and lower).
* Changing pipette approach angle (a higher angle seemed to make the situation a bit better, but not enough)
* Changing intracellular and extracellular solutions
Any suggestions would be highly appreciated.