TRANSFECTED RAT MU-OPIOID RECEPTORS (RMOR1 AND RMOR1B) STIMULATE PHOSPHOLIPASE-C AND CA2+ MOBILIZATION

THE mu opioid agonist DAMGO increases intracellular Ca2+ concentration and inositol triphosphate formation in Chinese hamster ovary cells st ably expressing the CL opioid receptors rMOR1 and rMOR1B, a recently i solated isoform of rMOR1. The increase in intracellular Ca2+ concentra tion is due solely to mobilization from internal stores. Both the DAMG O-induced stimulation of inositol triphosphate and increase in intrace llular Ca2+ concentration is similar for both variants with an EC(50) Of about 1 mu M, which is about an order of magnitude less efficient t han the inhibition of adenylyl cyclase (EC(50) = 150 mu M).