It is known that opioids inhibit the hypoxic ventilatory response in part via an action at the carotid body, but little is known about the cellular mechanisms that underpin this. This study’s objectives were to examine which opioid receptors are located on the oxygen-sensing carotid body type I cells from the rat and determine the mechanism by which opioids might inhibit cellular excitability.

Immunocytochemistry revealed the presence of μ and κ opioid receptors on type I cells. The μ-selective agonist DAMGO (10 μM) and the κ-selective agonist U50-488 (10 μM) inhibited high K+induced rises in intracellular Ca2+ compared with controls. After 3 h incubation (37 °C) with pertussis toxin (150 ng ml−1), DAMGO (10 μM) and U50-488 (10 μM) had no significant effect on the Ca2+response to high K+.

These results indicate that opioids acting at μ and κ receptors inhibit voltage-gated Ca2+ influx in rat carotid body type I cells via Gi-coupled mechanisms. This mechanism may contribute to opioid’s inhibitory actions in the carotid body.