Hyperpolarizing effects of dopamine on chemoreceptor nerve endings from cat and rabbit carotid bodies in vitro

Abstract

The effects of dopamine on DC potential changes recorded from the carotid sinus nerve were studied in vitro using carotid bodies and associated sinus nerves removed from anesthetized cats and rabbits. The carotid body was placed in one compartment of a superfusion chamber and was superfused with buffered salt solution. The carotid sinus nerve was led into an adjoining compartment, containing light-weight mineral oil, for recording DC potential changes with chlorided Ag electrodes. Dopamine injected into the superfusing solution in amounts of 50-250 .mu.g caused hyperpolarization of the DC potential. This effect occurred repeatedly in each preparation, the maximum number of tests in any 1 preparation being 27. In the same preparations, acetylcholine (50-100 .mu.g) and NaCN (10-20 .mu.g) caused depolarizations of the DC potential, effects previously described. The hyperpolarizing effects of dopamine were reduced or abolished by the .alpha.-adrenergic antagonists, dihydroergotamine (10-100 .mu.g/ml) and phenoxybenzamine (5 .mu.g/ml) and the dopamine antagonist droperidol (10-25 .mu.g/ml). The inhibitory effects of dopamine on the frequency of carotid body chemosensory discharges in cats and rabbits are apparently due to hyperpolarization of chemoreceptor afferent nerve endings and not necessarily to local vascular effects in the carotid body.