Development of a platinized platinum/iridium electrode for use in vitro.

Silver/silver chloride (Ag/AgCl) electrodes possess excellent electrical properties for measuring the electrical activity of gastrointestinal smooth muscle but exert toxic effects on this tissue in vitro. We thus developed a platinum electrode for use in vitro, the construction of these electrodes relying upon the formation of a glass-platinum/iridium seal. The platinum/iridium (Pt/Ir) electrodes were platinized using a current density of 0.45 mA mm-2. The electrode impedance at 0.01 Hz showed a minimum with platinization current-time products greater than 500 mA s mm-2. However, deposits in excess of 600 mA s mm-2 were readily removed by mechanical abrasion and proved unsatisfactory. Optimal platinization was obtained with a deposit of platinum-black corresponding to a current-time product of 550 mA s mm-2. Optimally-platinized electrodes (geometric surface area 0.11 mm2) had a stable and reproducible potential with a drift of less than 1 microV min-1 and a lower impedance than optimally chlorided silver electrodes (geometric surface area 0.46 mm2) at frequencies higher than 0.25 Hz. The platinized Pt/Ir electrodes were used to record the electrical activity of gastrointestinal smooth muscle in vitro.