Cannabinoid CB1 receptor elevation of intracellular calcium in neuroblastoma SH-SY5Y cells: Interactions with muscarinic and δ-opioid receptors

Although coupled to Gi/o proteins, cannabinoid CB1 receptors can also activate intracellular Ca2+ ([Ca2+]i) accumulation through not fully understood mechanisms. We report that in, human neuroblastoma SH-SY5Y cells, CB1 activation with the specific agonist arachidonoylchloroethanolamide (ACEA), weakly elevates [Ca2+]i and that this effect, when using low (1-100 nM) concentrations of ACEA, is enhanced by the previous activation of Gq/11-coupled M3 muscarinic receptors with carbachol, dose-dependently and up to ∼ 8-fold. A similar behaviour was also observed with carbachol and the Gi/o-coupled δ-opioid receptor. Furthermore, stimulation of CB1 receptors produced a concentration-dependent leftward shift of the elevation of [Ca2+]i by δ-opioid receptors. These stimulatory effects were variedly attenuated by selective antagonists of each receptor, pertussis toxin, inhibitors of phospholipase C (U73122 and D609), and, when assessed in the presence of extracellular Ca2+, by the block of voltage-activated calcium channels. Cholera toxin only slightly inhibited the Gq/11-Gi/o-mediated cross-talk, but induced a stronger inhibition of the Gi/o-Gi/o-mediated interaction. These findings suggest that activation of M3 muscarinic receptors might produce a qualitative alteration of the signaling associated with Gi/o-coupled receptors, and that sequential activation of CB1 and δ-opioid receptors, both coupled to Gi/o, produces instead synergistic effects on [Ca2+]i elevation.