we never firepolish, and getting a gigaseal has never been a problem. (pyramidal neurons, hippocampal neurons, purkinje cells (in slices, in vivo, or in culture) and hek293 cells. we use 1.5 mm OD thick wall borosilicate glass, 4-5 mohm resistance. apply about 0.2 ml of pressure and dimple the cell, withdraw the pressure and the resulting suction should be enough to form a gigaseal. if not, give a little more suction, but not much. i break the membrane slowly with additional suction after the gigaseal has former. don't wait too long after you get a giga seal to break the membrane (otherwise you pull too much membrane up into the pipette).