Arthropod D2 receptors positively couple with cAMP through the Gi/o protein family

The pyloric network is an important model system for understanding neuromodulation of rhythmic motor behaviors like breathing or walking. Dopamine (DA) differentially modulates neurons within the pyloric network. However, while the electrophysiological actions of DA have been well characterized, nothing is known about the signaling events that mediate its effects. We have begun a molecular characterization of DA receptors (DARs) in this invertebrate system. Here, we describe the cloning and characterization of the lobster D2 receptor, D2αPan. We found that when expressed in HEK cells, the D2αPan receptor is activated by DA, but not other monoamines endogenous to the lobster nervous system. This receptor positively couples with cAMP through multiple Gi/o proteins via two discrete pathways: 1) a Gα mediated inhibition of adenylyl cyclase (AC), leading to a decrease in cAMP and 2) a Gβγ-mediated activation of phospholipase Cβ (PLCβ), leading to an increase in cAMP. Alternate splicing alters the potency and efficacy of the receptor, but does not affect monoamine specificity. Finally, we show that arthropod D2 receptor coupling with cAMP varies with the cellular milieu.