A time domain determination of properties of voltage clamped cells, using a small white noise

The aim of the authors' study was to provide an efficient computer automated method for real time determination of the passive properties of voltage clamped cells with the smallest possible stimulation amplitude. The method had to be able to determine a wide range of time constants. The authors applied the correlation technique with a binary noise generator. This technique provides the impulse response which is a discrete sum of exponentials analyzed with the Pade-Laplace method. A logarithmic scale sampling enables the investigation of a large range of time constants with little computation. On a simple model composed of a membrane resistance (Rm), capacitance (Cm) and a access resistance (Rs), the authors found in particular that this method provides a cell capacitance estimate insensitive to large changes of Rs/Rm ratio. This method possesses some specific advantages over FFT based ones, and could be integrated into a digital amplifier for automated measurements.