Dual-frequency method for synchronous measurement of cell capacitance, membrane conductance and access resistance on single cells.
A dual-frequency method was developed to monitor changes of membrane capacitance, membrane conductance and serial resistance between patch pipette and cytoplasm of the cell in the whole-cell configuration. Measurement of real and imaginary components of cell admittance during excitation with two superimposed sinusoidal voltage of different frequencies provides mathematical solutions for all three variables. The validity of the method was verified with experiments on mast cells and exocrine pancreatic acinar cells. During degranulation of mast cells, induced by GTP gamma S in the pipette solution, a stepwise increase in membrane capacitance could be observed, indicating that the resolution of the method is below 10 fF. Precalibration of the setup allows all calculated data to be expressed as absolute values. The capacitance measurement proved to be rather independent of changes in the access resistance and in the cell membrane resistance over a wide range. The huge changes in membrane conductance of mouse pancreatic acinar cells during hormonal stimulation with acetylcholine produced a relative error of less than 0.3% in the capacitance trace. This allows a clear distinction between changes of membrane conductance and cell capacitance. The method therefore offers great advantages in the study of exocytosis as well as endocytosis in cell types, such as exocrine gland cells, with major changes in membrane conductance during hormonal stimulation.