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 (Ra), membrane resistance (Rm), and membrane capacitance (Cm) often provides useful information regarding physiological changes in the cell. In particular, an increase in capacitance may indicate vesicle fusion events as occurs during exocytosis. Rapid capacitance changes are usually measured with a phase-sensitive detector set to a phase angle that is independent of resistance changes. However, this angle changes over time and may be difficult to determine in cells with a low membrane resistance. The present paper describes a technique for rapidly measuring Ra, Rm, and Cm by simultaneously applying two harmonic frequencies and calculating the passive parameters from the resultant electrode current. Calibration and operation are independent of the compensation circuit settings that may be set to null most of the electrode current. The technique may be implemented on a standard patch clamp setup without other specialized equipment and should be particularly useful for the study of cells that have low Rm or undergo rapid changes in Ra or Rm.