Bioelectric potentials in the carotid body.

Simultaneous recordings of focal slow potentials (sVs) and chemosensory discharges were made from cat carotid body-nerve preparations in situ. Chemoreceptor stimulants (100% N2, asphyxia, NaCN, ACh and nicotine), and depressants (100% O2, spontaneous gasps and dopamine) changed receptor polarization. sVs evoked by stimulants had a negative polarity whereas depressants elicited positive deflections. There was a direct correlation between maximal frequency of chemosensory discharges and peak sV amplitude when NaCN injections or N2 inhalation were used. However, cholinergic agents, dopamine and substance P evoked sVs which lacked correlation in time-course, amplitude or polarity with changes in sensory frequency. After a 6-day carotid nerve crush, different stimuli still evoked sVs even in the absence of sensory discharges. Both sVs and chemosensory discharges were abolished after 1 h ischemia produced by ligature of carotid body blood vessels. Thus, sVs from carotid body chemoreceptors probably include a neuronal component (the generator potential) directly responsible for the origin of chemosensory discharges, and a non-neuronal component (receptor or secretory potentials) probably originating in glomus and/or sustentacular cells.