Geometric Parameters of Pipettes and Membrane Patches

Abstract

The object of the patch current measurement is a small membrane patch and a pipette tip of comparable dimensions. Both are at the limit of resolution of the optical microscope. Only rarely is it possible to “see” the membrane patch during the experiment, and even then quantitative evaluation of its size is impossible or difficult. The purpose of this chapter is to provide some hints toward estimation of the tip geometry of patch pipettes and of patch sizes by a combination of light and electron microscopy and electrical measurements. It should be emphasized, however, that there are wide variations in tip geometry and patch sizes, even if all the parameters that are under control of the experimenter are kept constant. The numbers given should therefore only be considered as order-of-magnitude estimates.