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

Although coupled to G(i/o) proteins, cannabinoid CB(1) receptors can also activate intracellular Ca(2+) ([Ca(2+)](i)) accumulation through not fully understood mechanisms. We report that in, human neuroblastoma SH-SY5Y cells, CB(1) activation with the specific agonist arachidonoylchloroethanolamide (ACEA), weakly elevates [Ca(2+)](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 CB(1) receptors produced a concentration-dependent leftward shift of the elevation of [Ca(2+)](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 Ca(2+), 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 CB(1) and delta-opioid receptors, both coupled to G(i/o) produces instead synergistic effects on [Ca(2+)] elevation.