Abstract

It has been proposed that OX₁ orexin receptors and CB₁ cannabinoid receptors can form heteromeric complexes, which affect the trafficking of OX₁ receptors and potentiate OX₁ receptor signaling to extracellular signal–regulated kinase (ERK). We have recently shown that OX₁ receptor activity releases high levels of the endocannabinoid 2-arachidonoyl glycerol (2-AG), suggesting an alternative route for OX₁-CB₁ receptor interaction in signaling, for instance, in retrograde synaptic transmission. In the current study, we set out to investigate this possibility utilizing recombinant Chinese hamster ovary K1 cells. 2-AG released from OX₁ receptor–expressing cells acted as a potent paracrine messenger stimulating ERK activity in neighboring CB₁ receptor–expressing cells. When OX₁ and CB₁ receptors were expressed in the same cells, OX₁ stimulation–induced ERK phosphorylation and activity were strongly potentiated. The potentiation but not the OX₁ response as such was fully abolished by specific inhibition of CB₁ receptors or the enzyme responsible for 2-AG generation, diacylglycerol lipase (DAGL). Although the results do not exclude the previously proposed OX₁-CB₁ heteromerization, they nevertheless unequivocally identify DAGL-dependent 2-AG generation as the pivotal determinant of the OX₁-CB₁ synergism and thus suggest a functional rather than a molecular interaction of OX₁ and CB₁ receptors.