Frequency-dependent membrane impedance in Chara corallina estimated by Fourier analysis

The white noise method of measuring membrane impedance has been applied to internodal cells of Chara corallina . Fourier analysis of a white noise transmembrane current signal and the voltage response has been used to obtain the frequency-dependent impedance of the in-series combination of the plasmalemma and tonoplast membranes. The results are similar to those of other workers who have measured membrane impedances by different techniques. At very low frequencies the equivalent capacitance of the membrane treated as an RC-circuit becomes negative, indicating a pseudoinductive effect. Membrane impedance has been measured over a range of pH values from pH 5.2 to pH 11: impedance magnitude reaches a maximum at pH 7. At interesting effect of fusicoccin at pH 11 has been observed, in which a decrease in membrane conductance occurs simultaneously with a small hyperpolarization of membrane PD.