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 c apacitance, membrane conductance and serial resistance between patch p ipette and cytoplasm of the cell in the whole-eel configuration. Measu rement of real and imaginary components of cell admittance during exci tation with two superimposed sinusoidal voltages of different frequenc ies provides mathematical solutions for all three variables. The valid ity of the method was verified with experiments on mast cells and exoc rine pancreatic acinar cells. During degranulation of mast cells, indu ced by GTP gamma S in the pipette solution, a stepwise increase in mem brane capacitance could be observed, indicating that the resolution of the method is below 10 fF. Precalibration of the setup allows all cal culated data to be expressed as absolute values. The capacitance measu rement proved to be rather independent of changes in the access resist ance and in the cell membrane resistance over a wide range. The huge c hanges 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 distincti on between changes of membrane conductance and cell capacitance. The m ethod 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.