Abstract
The pharmacology of G protein-coupled receptors can be influenced by factors such as constitutive receptor activation and Na+ ions. In this study, we examined the coupling of natively and heterologously expressed nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptors with voltage-dependent Ca2+ channels after exposure to four high-affinity NOP receptor blockers [[Nphe1Arg14Lys15]N/OFQ-NH2 (UFP-101), 1-[1-(cyclooctylmethyl)-1,2,3,6-tetrahydro-5-(hydroxymethyl)-4-pyridinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (Trap-101), 1-benzyl-N-{3-[spiroisobenzofuran-1(3H),4′-piperidin-1-yl]propyl}pyrrolidine-2-carboxamide (compound 24), and N-(4-amino-2-methylquinolin-6-yl)-2-(4-ethylphenoxymethyl)benzamide hydrochloride (JTC-801)] in sympathetic neurons. The enhanced tonic inhibition of Ca2+ currents in the absence of agonists, indicative of constitutively active NOP receptors in transfected neurons, was abolished after pretreatment with pertussis toxin. In control neurons, the four antagonists did not exert any effects when applied alone but significantly blocked the N/OFQ-mediated Ca2+ current inhibition. Exposure of transfected neurons to UFP-101 resulted in partial agonist effects. In contrast, Trap-101, compound 24, and JTC-801 exerted inverse agonism, as measured by the loss of tonic Ca2+ current inhibition. In experiments designed to measure the N/OFQ concentration-response relationship under varying Na+ concentrations, a leftward shift of IC50 values was observed after Na+ exposure. Although similar N/OFQ efficacies were measured with all solutions, a significant decrease of Hill coefficient values was obtained with increasing Na+ concentrations. Examination of the allosteric effects of Na+ on heterologously overexpressed NOP receptors showed that the tonic Ca2+ current inhibition was abolished in the presence of the monovalent cation. These results demonstrate that constitutively active NOP receptors exhibit differential blocker pharmacology and allosteric regulation by Na+. Data are also presented demonstrating that heterologously expressed μ opioid receptors in sympathetic neurons are similarly modulated.
Footnotes
This work was supported by the National Institutes of Health National Institute on Drug Abuse [Grant R01-DA025574] and Tobacco Settlement Funds from the Pennsylvania Department of Health.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.109.062208.
-
ABBREVIATIONS:
- GPCR
- G protein-coupled receptor
- NOP
- nociceptin/orphanin FQ peptide
- N/OFQ
- nociceptin/orphanin FQ
- SG
- stellate ganglion
- MOP
- μ opioid peptide
- Trap-101
- 1-[1-(cyclooctylmethyl)-1,2,3,6-tetrahydro-5-(hydroxymethyl)-4-pyridinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one
- compound 24
- 1-benzyl-N-{3-[spiroisobenzofuran-1(3H),4′-piperidin-1-yl]propyl}pyrrolidine-2-carboxamide
- UFP-101
- [Nphe1Arg14Lys15]N/OFQ-NH2
- JTC-801
- N-(4-amino-2-methylquinolin-6-yl)-2-(4-ethylphenoxymethyl)benzamide hydrochloride
- PTX
- pertussis toxin
- DAMGO
- [d-Ala2-N-Me-Phe4-Glycol5]-enkephalin
- CTAP
- d-Phe-Cys-Tyr-d-Trp-Arg-Thr-Pen-Thr-NH2
- NMG
- N-methyl-d-glucamine
- TEA-OH
- tetraethylammonium hydroxide
- J-113397
- (±)-1-[(3R*,4R*)-1-(cyclooctylmethyl)-3-(hydroxymethyl)-4-piperidinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one.
- Received November 6, 2009.
- Accepted February 16, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|