Measurement of cell impedance in frequency domain using discontinuous current clamp and white-noise-modulated current injection

A method is decribed for the determination of cellular input impedance of non-spiking neurones. The input impedance is important when cellular geometry and the effects of voltage-dependent channels are considered. Cells are impaled with a single glass microelectrod and current is injected using a time-sharing technique. The cell's impedance is measured by randomly modulating the injected current and calculating the impedance as a transfer function between current and recorded membrane voltage. Corresponding coherence functions can also be calculated for estimating the signal-to-noise ratio, and also linearity (i.e. possible activation of voltage-dependent conductances) of the membrane.