I would like to measure whole-cell currents in HEK cells. I have no problem achieving a GOhm seal, and sometimes I also succeed in going whole cell. But, mostly, when I try to rupture the membrane, the seal breaks. I used both suction and the ZAP function of my Axopatch 200B amplifier, to no avail. My pipette resistances are btw. 4 and 5 MOhms, as these are supposed to be optimal for whole-cell recording. I would be very grateful for any suggestions how to solve this problem.