A new single sucrose-gap method allowing current to be injected and the resulting potential change to be recorded

A novel single sucrose-gap technique which allows the injection of current and the recording of the resulting change in the gap potential has been developed. Current injection is achieved discontinuously at a chopping rate of between 500 Hz and 5 kHz and the gap potential is recorded during the off-period of current injection and held until the next sampling period. This approach eliminates the potential drop in the sucrose solution and makes the measurement of electrical properties possible with a single sucrose-gap technique. Membrane properties of the dorsal roots of the bullfrog were examined using this technique. An outward-going rectification was evident around the resting potential and an inward-going rectification appeared on hyperpolarization below -70 mV. This rectification gave rise to a sigmoidal relationship between voltage and current. Hyperpolarization in response to current injection revealed a very long charging time constant. These observed membrane characteristics were in general agreement with those intracellulary recorded from the thick myelinated fiber in the frog dorsal roots.