I've been doing perforated and whole-cell patch clamp in my lab with isolated vomeronasal sensory neurons for about 3 years now. I've had problems in the past, but these have always been solved by new solutions, new filters, changing puller settings for better electrode tips, better cell isolation, etc.
Recently and very suddenly, I've been having problems where my seals will not form beyond 400mOhms (700mOhms if I'm lucky). I've already put on a new electrode holder, new O-rings, and new tubing/syringe to no avail. I know it is not the cells, as the problem persists even if my labmates isolate cells for me with their solutions when they have been getting good cells/gigaseals. The odd thing is that there will be a day every two weeks or so where I can get great seals and very stable whole-cell configurations.
Regardless of if the seals stabilize at 400mOhms or are > 1GOhm, it takes much longer to seal then it used to (about 20 minutes as opposed to 5 or 10 minutes). Another very strange thing is that when switching from seal test to membrane test in Clampex where the cell is voltage-clamped at -60mV, I always see a drop in the membrane resistance (for example, from 40mOhms to 30mOhms). This has never happened before; even with cells that in the end would never seal STILL have at least some increase in the membrane resistance when switching to membrane test. I have checked the model cell on my headstage, and all of the electrical parameters are normal.
I'm beginning to suspect that I may have electrode drift, which I will need to check, but doses anyone have other suggestions? Thank you for reading.