Testing electrode suitability for field stimulation of high-threshold biological preparations

Introduction: A problem posed by electrical field (E) stimulation of biological preparations with high excitation threshold is that the E intensity required for excitation is likely to induce water electrolysis at the electrode surface, which can alter the extracellular medium and cause deleterious effects on the cells. In this study, different electrode materials and geometries were tested aiming at identifying electrode configurations that could transduce the E intensity required for exciting ventricular cardiomyocytes isolated from neonatal rats (threshold E ~30 V/cm) without causing water electrolysis. Methods: Wire and plate electrodes made of platinum, stainless steel and nickel/chrome alloy were used. The effect of blasting the electrode surface with sand and NaHCO3 solution was also tested. Electrodes were inserted into a cell perfusion chamber containing the saline solution routinely used for physiological experiments. During E application for 5 min, the electrode surface and its surroundings were examined at high magnification for the presence of microbubbles, which indicates the occurrence of water electrolysis. The greatest E intensity applied that failed to generate microbubbles (En) was estimated. Results: While nickel/chrome and stainless steel electrodes resulted in low En values, the best performance was observed for sandblasted platinum wire (2 mm diameter) and plate (25 mm x 5 mm; 0.1 mm thickness) electrodes, for which En was ≥40 V/cm. Conclusion: These electrode configurations are suitable for effective and safe stimulation of isolated neonatal cardiomyocytes.