The Electrical Properties of Plant Cell Membranes. II.* Distortion of Non-linear Current-Voltage Characteristics induced by the Cable Properties of Chara

Abstract

The electrical 'cable' properties of cylindrical, radially symmetric cells with non-linear membrane current-voltage (I-V) characteristics are considered. A numerical technique is described whereby, from a knowledge of the membrane I-V characteristics and the cellfelectrode geometry, it is possible to calculate the I-V characteristics that would be actually measured after distortion by the cable properties of the cell. Thus it is shown that the I-V characteristics of charophytes such as Chara and Nitella measured in some common experimental configurations can be significantly different from the actual I-V characteristics of the membrane. This distortion will always tend to linearize the measured I-V characteristics and consequently a major problem is that the magnitude of any such linearization cannot be simply estimated. In particular if the measured conductance increases with increasing magnitude of V, it is very difficult to determine the actual shape of the membrane I-V characteristics. However an iterative procedure is described which will permit derivation of the correct intrinsic membrane I-V characteristics from the distorted measured I-V characteristics, providing that V is measured at the point of current injection. This procedure is applied to some experimental I-V data of Chara to demonstrate the possible magnitude of the distortion arising from the cable properties.