Depolarization of sensory nerve endings and impulse initiation in common carotid baroreceptors.

1. Electrical events in the peripheral nerve terminals of baroreceptors were investigated following isolation and identification of receptive fields innervated by single baroreceptor fibres. A slow potential change, that is a local depolarization which had the characteristics of a generator (receptor) potential, was recorded from the common carotid baroreceptor fibres at a point close to the sensory terminals.2. The slow potential increased in amplitude with increasing stimulus strength and its time course increased with increasing duration of the mechanical stimulus. Action potentials were initiated from the slow potential when the applied mechanical stimulus was suprathreshold.3. The slow potentials evoked by a train of subthreshold stimuli summed to evoke action potentials.4. When a high-frequency train of suprathreshold stimuli was applied to the baroreceptors, the slow potential following a preceding one from which an action potential was initiated failed to fire the nerve fibre.5. When the sodium content of the Ringer-Locke solution was decreased, the slow potential remained after blockage of the action potential.6. The slow potential remained after abolishing the spike potential by application of tetrodotoxin.