Recording of action potentials and polarization of a single crayfish motor axon through a sucrose-gap capillary suction electrode

Summary A capillary suction electrode was developed which contains in its tip a sucrose-gap. The nerve fiber is pulled by negative pressure through the closely fitting openings of an outer and an inner capillary. The space between these openings is o.1 mm wide and can be perfused with sucrose solution. Because of the small physical size of the electrode tip the electrode can be used to record from single unmyelinated nerve fibers in small preparations in combination with other electrodes or transducers.Action potentials were recorded from branches of the motor axon of the opener muscle of the crayfish claw. The amplitude of the recorded action potentials was 7–22 mV, and all records were monophasic positive. The action potential showed depolarizing but not hyperpolarizing afterpotentials.Hyperpolarization of the nerve fiber by –0.05 to –0.2 A current injected through the recording electrode led to about 50% increase in the amplitude of the recorded action potentials and to a marked prolongation of the depolarizing afterpotentials. Depolarization of the fiber decreased the amplitude of the action potential.This work was supported by the Deutsche Forschungsgemeinschaft.