Simplified method for setting the phase angle used in capacitance measurements in studies of exocytosis

Phase detectors (lock-in amplifiers) have been used in conjunction with patch-clamp apparatus to follow the time course of exo- and endocytotic processes. A critical step is accurate setting of the phase to separate signals due to conductance changes from those due to capacitance changes. It has been the practice to obtain this setting empirically. Analysis of the admittance, and its derivatives, of a model equivalent circuit used commonly in this field shows that the desired phase setting is just twice the phase shift of the current relative to the stimulus voltage, which is easily, accurately and quickly determined. This fact permits rapid and accurate setting of the desire phase angle for those cells to which the equivalent circuit is suitable.