Coupling Resistance of Double Barrelled Microelectrodes

Abstract

THE double barrelled microelectrode¹ is a convenient way of introducing two electrode tips into the same cell for simultaneously passing a current and recording. The chief source of artefact is the coupling resistance (Rc) (ref. 2), which is manifest when a current passed through the stimulating barrel causes a voltage to appear at the recording barrel. It presumably represents the resistance of electrolyte immediately adjacent to and shared by both tips, for most of it disappears if the very tip of the electrode is broken off. When current is passed from an intracellular double barrelled electrode, the coupling resistance with the electrode intracellular (Rc_i) is in series with the cell membrane resistance viewed by the recording barrel. Rc_i must therefore be subtracted from the observed input resistance to obtain the true value of the input resistance and of voltage displacements. The problem is to know the value of Rc_i, because Rc_i can only be measured directly with the electrode extracellular. The simplest method² is to assume that Rc_i does not change on impalement, which is to assume that Rc_i is the same as Rc_i—the value obtained on withdrawal from the same cell.