A convenient electrode holder for glass pipettes to stabilize electrode potentials

Electrophysiological techniques require stable, reversible electrodes for accurate recording. Ag/AgCl electrodes are commonly used in patch-clamp and intracellular recording pipettes, but when these electrodes are exposed to Cl^- free media they are no longer reversible and may develop large, unstable offset potentials. We present here a simple electrode holder design that provides a liquid junction between the electrode solution and a KCl- filled reservoir containing the AgCl pellet. This allows an electrode solution of any composition to be used without affecting the reversibility of the electrode, and the liquid junction potentials that develop are small and well defined. Mechanical isolation of the AgCl pellet from the pipette improves long-term stability of the electrode because the AgCl coating is not scraped while changing pipettes. The response time of the holder and its wide-band noise levels are comparable to those of standard holders. For practical experiment durations, the diffusion for KCl from the reservoir down the pipette produces negligible contamination at the tip. Similarly, back diffusion of the pipette contents into the reservoir is also negligible.