Pressure polishing: a method for re-shaping patch pipettes during fire polishing

The resolution of patch-clamp recordings is limited by the geometrical and electrical properties of patch pipettes. The ideal whole-cell patch pipette has a blunt, cone-shaped tip and a low resistance. The best glasses for ma king patch pipettes are low noise, low capacitance glasses such as borosili cate and aluminasilicate glasses. Regrettably, nearly all borosilicate glas ses form pipettes with sharp, cone-shaped tips and relatively high resistan ce. It is possible, however, to reshape the tip during fire polishing by pr essurizing the pipette lumen during fire polishing, a technique we call 'pr essure polishing.' We find that this technique works with pipettes made fro m virtually any type of glass, including thick-walled aluminasilicate glass . We routinely use this technique to make pipettes suitable for whole-cell patch-clamp recording of tiny neurons (1-3 mu m in diameter). Our pipettes are made from thick-walled, borosilicate glass and have submicron tip openi ngs and resistances < 10 M Omega. Similar pipettes could be used to record from subcellular neuronal structures such as axons, dendrites and dendritic spines. Pressure polishing should also be useful in patch-clamp applicatio ns that benefit from using pipettes with blunt tips, such as perforated-pat ch whole-cell recordings, low-noise single channel recordings and experimen ts that require internal perfusion of the pipette. (C) 2000 Elsevier Scienc e B.V. All rights reserved.