TY - JOUR T1 - μ-Opioid-Induced Desensitization of Opioid Receptor-Like 1 and μ-Opioid Receptors: Differential Intracellular Signaling Determines Receptor Sensitivity JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 965 LP - 972 DO - 10.1124/jpet.103.051599 VL - 306 IS - 3 AU - Chitra D. Mandyam AU - Deepak R. Thakker AU - Kelly M. Standifer Y1 - 2003/09/01 UR - http://jpet.aspetjournals.org/content/306/3/965.abstract N2 - μ-Opioid receptors have been shown to contribute to orphanin FQ/nociceptin (OFQ/N)-mediated analgesia and hyperalgesia, indicating that both pro- and antinociceptive actions of OFQ/N are influenced by μ-opioid receptors. A 60-min activation of μ-or opioid receptor-like 1 (ORL1) opioid receptors natively expressed in BE(2)-C human neuroblastoma cells desensitized both μ- and ORL1 receptor-mediated inhibition of cAMP accumulation. The mechanism(s) of OFQ/N-mediated μ- and ORL1 cross talk involves the conventional protein kinase C isozyme, PKC-α, and G protein-coupled receptor kinases (GRKs) 2 and 3. Unlike OFQ/N-mediated desensitization of ORL1 and μ-opioid receptors, [d-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO)-mediated ORL1 desensitization in BE(2)-C cells is PKC-independent. However, DAMGO (1 μM) pretreatment increased membrane levels of GRK2 and GRK3, indicating their translocation to the membrane upon activation. This suggests that DAMGO activation of μ-opioid receptors results in GRK2 and GRK3 inactivation of ORL1 upon challenge with OFQ/N. Antisense, but not sense, DNA selectively targeting GRK2 or GRK3 blocks DAMGO-mediated μ- and ORL1 desensitization, respectively. However, in SH-SY5Y neuroblastoma cells, DAMGO failed to desensitize ORL1 or alter membrane PKC-α or GRK levels. Instead, DAMGO stimulated PKC-ϵ translocation to the cell membrane and produced μ-receptor desensitization. These results indicate that acute exposure to μ-receptor agonists can regulate ORL1 function, but the ability to do so varies from cell type to cell type. These results also confirm the existence of multiple signaling mechanisms for μ-opioid receptors and the importance of these mechanisms for μ-receptor-mediated-heterologous effects. The American Society for Pharmacology and Experimental Therapeutics ER -