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Cannabinoid CB2 receptors may couple to a variety of G proteins and intracellular effector systems to regulate physiological and pathophysiological processes involved in inflammatory and neuropathic pain. In this study, the coupling of cannabinoid hCB2 receptors to G[alpha]qo5 and G[alpha]qi5 proteins was studied and compared by investigating the pharmacological properties of HEK-293 cells co-expressing cannabinoid hCB2 with chimeric G[alpha]qo5 (HEK-hCB2-Gqo5) or G[alpha]qi5 (HEK-hCB2-Gqi5). Both cell lines were found to be amendable for measuring cannabinoid CB2 receptor agonist evoked Ca2 mobilization in a high-throughput manner. Comparison of binding affinities of ligands in homogenates prepared from both cell lines revealed similar affinities for [3H]CP55,940 displacement with the following rank order: CP55,940 ~ WIN55,212-2 > SR144528 > JWH015 ~ AM1241 ~ AM630 > SR141617A ~ AM251. In comparison at cannabinoid hCB1 receptors: the rank order was: SR141617A ~ CP55,940>AM251 > WIN55,212-2 > AM1241 ~ SR144528 > JWH015 ~ AM630. No significant differences in cannabinoid receptor agonist (CP55,940 ~ WIN55,212-2 > JWH015) or antagonist (SR144528 ~ AM1241 > AM630 > AM251 ~ SR141617A) profiles were observed in HEK-hCB2-Gqo5 and HEK-hCB2-Gqi5 cells as determined using intracellular Ca2 measurements. Experiments with HEK-hCB2-Gqi5 cells carried out by investigating interactions among CP55,940, carbachol, thapsigargin, and U73122 revealed that the mechanism of cannabinoid hCB2 receptor coupling via chimeric G proteins to Ca2 mobilization involves phospholipase C-inositol trisphosphate (PLC-IP3) and that it is less efficient in comparison to the endogenous muscarinic mediated PLC-IP3-Ca2 pathway. This study demonstrates that expressed cannabinoid CB2 receptors couple equally well to G[alpha]qo5 and G[alpha]qi5 proteins and that receptor agonist or antagonist pharmacology is not influenced by the nature of these coupled G proteins when heterologously expressed.

(C) 2009Elsevier, Inc.