The interpretation of intracellular measurements of membrane potential, resistance, and coupling in cells of higher plants.

Results of microelectrode impalements of parenchymal cells of coleoptiles made in several different laboratories differ widely. The highest membrane potentials correlate with lower input resistance and the presence of intercellular coupling, whereas high input resistance seems to be associated with an absence of measurable coupling and possibly lower membrane potentials. In this paper we demonstrate that these results are consistent with (1) a tonoplast resistance several times greater than the input resistance of the cytoplasmic compartment, and (2) the presence of variable amounts of shunting introduced by insertion of the microelectrode through the cell membranes. The general consequences of this hypothesis are developed quantitatively. If the ideas are applicable to other tissues of higher plants-and on this point the evidence is still insufficient to judgeboth the design of experiments and the interpretation of measurements made with microelectrodes will have to be reevaluated.