Nitric oxide modulates the physiological control of ciliary activity in the marine mussel Mytilus edulis via morphine: novel mu opiate receptor splice variants.

OBJECTIVES: The study sought to determine how dopamine controls ganglionic processes involved with modulating lateral cilia beating via the peripheral branchial nerve.

METHODS: The lateral cilia found on the gill filaments exhibit metachronal ciliary beating determined stroboscopically. Novel opiate receptors were determined pharmacologically and demonstrated by RT-PCR and sequence analysis of total RNA from Mytilus edulis visceral ganglia.

RESULTS: Dopamine applied to the visceral ganglion inhibits the activity of lateral cilia in a concentration and haloperidol sensitive manner. Morphine or DAMGO significantly enhances ciliary beating in a naloxone sensitive manner, whereas L-NAME, a nitric oxide synthase inhibitor, only antagonized morphine's action. SNAP, a nitric oxide donor, also enhanced lateral ciliary beating rates. Supporting the observation, i.e., morphine sensitive nitric oxide enhancement of ciliary beating and DAMGO insensitive, that two different mu opiate receptors are present in this tissue, a 602 bp fragment of the human micro 3 opiate receptor and a 935 bp fragment, designated micro 4 have been demonstrated.

CONCLUSIONS: The lateral epithelium of the gill is innervated by serotonergic, cilioexcitatory neurons and dopaminergic, cilioinhibitory neurons, originating in the visceral ganglion. This data supports previous reports that demonstrate inhibiting ganglionic dopamine release allows the serotonin signals to prevail uncontrolled, enhancing ciliary rates. Supporting the observation that two different mu opiate receptors are present in this tissue, evidence is presented that identifies a 602 bp fragment of the human micro 3 opiate receptor and a 935 bp fragment, designated micro 4. Overall, the data strongly suggests that the two alternatively spliced mu opiate receptors may be involved in the physiological regulation of lateral ciliary activity in the visceral ganglia via dopamine and nitric oxide.