Method to determine whole-cell capacitance via square wave perturbation. For whole-cell recording from cells with time constants >50 μs, square pulses were employed at 0.5 kHz with an amplitude of 20 mV. Model current is shown in A. Peak current, a, and the projected steady-state current, b, were determined as described in Materials and methods. (B) Half of the current from a typical recording (dots) with the fitted exponential function used to determine cell parameters is shown. The asymptote of current was determined using the averages of three equally spaced data sections (dashed sections) according to Eq. 2, given in Materials and methods. The asymptote was subtracted and the data range from the peak to a point located at ∼3τ, estimated as peak current times e−3, was used to determine the exponential constants via linear regression of the log of the decaying current transient (solid line).
