Zf-and-Hsys-based Cm measurement under the whole-cell patch-clamp recording

Membrane capacitance (C(m)) measurement, which measures and monitors plasma membrane capacitance and its changes of a cell, is one of the most important quantitative techniques and widely used in the studies of exocytosis and endocytosis. We present here a Z(f)-and-H(sys)-based C(m) measurement method (Z-H method) for our self-developed patch-clamp amplifier (PCA). The method adopts the complex impedance of the feedback resistor of the PCA and a transfer function, H(sys), of the main and stimulus paths to generate the impedance of a patch-clamped cell, which extends Gillis' work for C(m) measurements. The chief advantage of the approach is that it does not depend on idealized assumptions about the impedance supplied to the probe input by measuring the frequency responses of the various components of the PCA. H(sys) is generated on "frequency grids" at different standard settings of the PCA, stored and managed by a simple database, and then retrieved for calculation of cell parameters, which results in a high efficiency. An algorithm for obtaining the trans-admittance of the slow capacitance compensation (C-slow) circuitry is provided to improve the accuracy of impedance measurements when the C-slow circuitry is turned on.