Kappa opioid receptor

The title of this article should be Kappa opioid receptor. The initial letter is capitalized due to technical restrictions.

The κ-Opioid receptors are a class of opioid receptors with dynorphins as the primary endogenous ligands, and ketazocine as a potent selective exogenous ligand. There are three variants: κ₁, κ₂, and κ₃.

Effects

It has long been believed that kappa-opioid receptor agonists are dysphoric. This misconception traces back to early articles in the 1980s about human tests with κ-opioid receptor agonists. It was stated that:

"Both doses of ketocyclazocine substantially elevated scores on the LSD subscale of the ARCI as did the high dose of cyclazocine (fig. 2C). Morphine failed to increase scores significantly on this scale which measures dysphoria."

It is now widely accepted that κ-opioid receptor (partial) agonists have hallucinogenic ("psychotomimetic") effects, as exemplified by salvinorin A. These effects are generally undesirable in medicinal drugs and could have had frightening or disturbing effects in the tested humans, but they are not per se dysphoric. It is thought that the hallucinogenic effects of drugs such as butorphanol, nalbuphine, and pentazocine serve to limit their opiate abuse potential. In the case of salvinorin A, a structurally novel neoclerodane diterpene κ-opioid receptor agonist, these hallucinogenic effects are sought after. While salvinorin A is considered a hallucinogen, its effects are qualitatively different than those produced by the classical psychedelic hallucinogens such as LSD or mescaline.

Activation of the κ-opioid receptor appears to antagonize many of the effects of the μ opioid receptor.

Kappa ligands are also known for their characteristic diuretic effects, due to their negative regulation of antidiuretic hormone (ADH).

Kappa agonism is neuroprotective against hypoxia/ischemia; as such, kappa receptors may represent a novel therapeutic target.

Location

κ receptors are located in the periphery by pain neurons, in the spinal cord and in the brain.

Reversal

Non-specific opioid receptor antagonists (e.g., naloxone) as well as the mixed opioid agonist/antagonist buprenorphine can be used to reverse the effects of kappa agonists.

Further reading

• Hatzoglou A, Bakogeorgou E, Kampa M, et al. (2000). Somatostatin and opioid receptors in mammary tissue. Role in cancer cell growth.. Adv. Exp. Med. Biol. 480: 55-63.
• Narita M, Funada M, Suzuki T (2001). Regulations of opioid dependence by opioid receptor types.. Pharmacol. Ther. 89 (1): 1-15.
• Simonin F, Gavériaux-Ruff C, Befort K, et al. (1995). kappa-Opioid receptor in humans: cDNA and genomic cloning, chromosomal assignment, functional expression, pharmacology, and expression pattern in the central nervous system.. Proc. Natl. Acad. Sci. U.S.A. 92 (15): 7006-10.
• Zhu J, Chen C, Xue JC, et al. (1995). Cloning of a human kappa opioid receptor from the brain.. Life Sci. 56 (9): PL201-7.
• Wang JB, Johnson PS, Wu JM, et al. (1994). Human kappa opiate receptor second extracellular loop elevates dynorphin's affinity for human mu/kappa chimeras.. J. Biol. Chem. 269 (42): 25966-9.
• Mansson E, Bare L, Yang D (1994). Isolation of a human kappa opioid receptor cDNA from placenta.. Biochem. Biophys. Res. Commun. 202 (3): 1431-7.
• Yasuda K, Espinosa R, Takeda J, et al. (1994). Localization of the kappa opioid receptor gene to human chromosome band 8q11.2.. Genomics 19 (3): 596-7.
• Chao CC, Gekker G, Hu S, et al. (1996). kappa opioid receptors in human microglia downregulate human immunodeficiency virus 1 expression.. Proc. Natl. Acad. Sci. U.S.A. 93 (15): 8051-6.
• Lee JW, Joshi S, Chan JS, Wong YH (1998). Differential coupling of mu-, delta-, and kappa-opioid receptors to G alpha16-mediated stimulation of phospholipase C.. J. Neurochem. 70 (5): 2203-11.
• Chatzaki E, Margioris AN, Makrigiannakis A, et al. (2000). Kappa opioids and TGFbeta1 interact in human endometrial cells.. Mol. Hum. Reprod. 6 (7): 602-9.
• Gomes I, Jordan BA, Gupta A, et al. (2001). Heterodimerization of mu and delta opioid receptors: A role in opiate synergy.. J. Neurosci. 20 (22): RC110.
• Mathieu-Kia AM, Fan LQ, Kreek MJ, et al. (2001). Mu-, delta- and kappa-opioid receptor populations are differentially altered in distinct areas of postmortem brains of Alzheimer's disease patients.. Brain Res. 893 (1-2): 121-34.
• Lokensgard JR, Gekker G, Peterson PK (2002). Kappa-opioid receptor agonist inhibition of HIV-1 envelope glycoprotein-mediated membrane fusion and CXCR4 expression on CD4(+) lymphocytes.. Biochem. Pharmacol. 63 (6): 1037-41.
• Li JG, Chen C, Liu-Chen LY (2002). Ezrin-radixin-moesin-binding phosphoprotein-50/Na+/H+ exchanger regulatory factor (EBP50/NHERF) blocks U50,488H-induced down-regulation of the human kappa opioid receptor by enhancing its recycling rate.. J. Biol. Chem. 277 (30): 27545-52.
• Suzuki S, Chuang LF, Yau P, et al. (2002). Interactions of opioid and chemokine receptors: oligomerization of mu, kappa, and delta with CCR5 on immune cells.. Exp. Cell Res. 280 (2): 192-200.
• Strausberg RL, Feingold EA, Grouse LH, et al. (2003). Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences.. Proc. Natl. Acad. Sci. U.S.A. 99 (26): 16899-903.
• McLaughlin JP, Xu M, Mackie K, Chavkin C (2003). Phosphorylation of a carboxyl-terminal serine within the kappa-opioid receptor produces desensitization and internalization.. J. Biol. Chem. 278 (36): 34631-40.
• Ota T, Suzuki Y, Nishikawa T, et al. (2004). Complete sequencing and characterization of 21,243 full-length human cDNAs.. Nat. Genet. 36 (1): 40-5.

External links

• IUPHAR GPCR Database - κ opioid receptor
• MeSH kappa+Opioid+Receptor