A NOVEL METHOD FOR RAPID MEASUREMENT OF MEMBRANE RESISTANCE, CAPACITANCE, AND ACCESS RESISTANCE

During patch clamp recordings, measurement of passive parameters such as access resistance (R(a)), membrane resistance (R(m)), and membrane capacitance (C-m) often provides useful information regarding physiolo gical changes in the cell. In particular, an increase in capacitance m ay indicate vesicle fusion events as occurs during exocytosis. Rapid c apacitance changes are usually measured with a phase-sensitive detecto r set to a phase angle that is independent of resistance changes. Howe ver, this angle changes over time and may be difficult to determine in cells with a low membrane resistance. The present paper describes a t echnique for rapidly measuring R(a), R(m), and C-m by simultaneously a pplying two harmonic frequencies and calculating the passive parameter s from the resultant electrode current. Calibration and operation are independent of the compensation circuit settings that may be set to nu ll most of the electrode current. The technique may be implemented on a standard patch clamp setup without other specialized equipment and s hould be particularly useful for the study of cells that have low R(m) or undergo rapid changes in R(a) or R(m).