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

Although coupled to G(i/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 G(q/11)-coupled M-3 muscarinic receptors with carbachol, dose-dependently and up to similar to 8-fold. A similar behaviour was also observed with carbachol and the G(i/o)-coupled delta-opioid receptor. Furthermore, stimulation of CB1 receptors produced a concentration-dependent leftward shift of the elevation of [Ca2+](i) by delta-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 G(q/11)-G(i/o)-mediated cross-talk, but induced a stronger inhibition of the G(i/o)-G(i/o)-mediated interaction. These findings suggest that activation of M-3 muscarinic receptors might produce a qualitative alteration of the signaling associated with G(i/o)-coupled receptors, and that sequential activation of CB1 and delta-opioid receptors, both coupled to G(i/o) produces instead synergistic effects on [Ca2+] elevation. (C) 2009 Elsevier B.V. All rights reserved.