Low-Impedance Capillary Electrode for Wide-Band Recording of Membrane Potential in Large Axons

An electrically floating platinized-platinum (Pt-Pt) wire within the length of a long (3-cm) electrolyte-filled glass capillary (100μ diam), which is used to monitor the internal potential in large axons, eliminates cable effects and lowers the effective electrode impedance to < 10 kΩ. With this low-source-impedance capillary electrode; absolute transmembrane potentials can be recorded and a fast-responding (0.5-μs) voltage-clamp system is obtained.