It has been found that mu-, delta- and kappa-opioid receptors that belong to G-protein-coupled receptors (GPCRs receptor group can form oligomeric complexes with each other (e.g., DOR-KOR, DOR-MOR) when co-expressed by the same cell. Pharmacological studies indicate that oligomers of opioid receptors react differently to opioid ligands in comparison to their corresponding homomers. Oligomerizatin can be both cell- and tissue-specific and can reflect a pathophysiological condition. There is a suggestion to treat oligomeric opioid receptors as a novel drug target group for which different opioid compounds have to be developed. In addition to differences in ligand selectivity and potency, it appears that desensitization/trafficking of oligomeric opioid receptors is controlled differently compared to homomeric receptors. Oligomerization of of opioid receptors represents a significant challenge in developing potent opioid analgesic compounds of high specificity and minimal negative side effects such as tolerance and dependence. In spite of recent advances in unraveling the process of oligomerization of opioid receptors the mechanisms underlying dynamic interactions between different types of opioid receptors to form heteromers/oligomers are not fully understood. It is not clear, for example, how many specific intracellular factors serve as shaperons that regulate oligomerization of opioid receptors and what controls their plasma membrane-cytoplasm cycling dynamics.
In this special guest issue on " Oligomerization & Trafficking of Opioid Receptors" in the Journal Cells, research articles, technical notes as well as reviews are grouped together to shed light on the mechanisms regulating oligomerization of opioid receptors and their trafficking within the cell. The intent of this special issue is to serve as a forum allowing cell biologists and pharmacologists to exchange their experimental data and theories that can help better understand cellular and biochemical mechanisms of the opioid receptor function.

Dr. Catia Sternini
Prof. Dr. Alexander E. Kalyuzhny
Guest Editor

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• mu-, delta- and kappa-opioid receptors
• bivalent opioid ligand
• FRET & BRET studies of oligomerization
• immunocytochemical analysis of oligomerization
• pain
• tolerance and dependence
• trafficking & desensitization of opioid receptors
• signal transduction