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.