Identification of three new alternatively spliced variants of the rat mu opioid receptor gene: Dissociation of affinity and efficacy Journal Article
| Authors: | Pasternak, D. A.; Pan, L.; Xu, J.; Yu, R.; Xu, M. M.; Pasternak, G. W.; Pan, Y. X. |
| Article Title: | Identification of three new alternatively spliced variants of the rat mu opioid receptor gene: Dissociation of affinity and efficacy |
| Abstract: | Mu opioid receptors mediate the pharmacological actions of morphine and morphine-like drugs, such as heroin. The mouse and human Oprm genes undergo splicing. In these present studies, we have identified and characterized three new MOR-1 splice variants from the rat Oprm gene. Using an RT-PCR approach, we isolated the new exons 7, 8 and 9 downstream of exon 3. The rat exons 7 and 9 were homologous to the mouse exons 7 and 9 while the rat exon 8 was not. Northern blot analysis with the new exon probes showed distinctive and abundant transcripts of the variants in the rat brain. Full-length cDNA clones containing the new exons, rMOR-1C1, rMOR-1C2 and rMOR-1D were obtained using an RT-PCR approach. Each contained the same exons 1, 2 and 3 as the original rMOR-1, followed by different combinations of the new exons in place of exon 4. In addition, we also isolated another new variant, rMOR-1A, which contains only exons 1, 2 and 3, and is homologous to the human variant MOR-1A previously identified. All the variants were highly mu-selective in binding studies with little difference in affinities for the mu ligands among the variants. However, functional evaluation of assessments of the variants using agonist stimulated [35S]GTPγS binding assays revealed marked differences among the variants, both in terms of potency and efficacy of the drugs. The relative efficacy of a series of mu opioids to each other varied depending upon the variant studied. Efficacy in the [35S]GTPγS assay did not correlate with either receptor binding affinity or with potency. Thus, selectivity of opioid action might be achieved by designing compounds with varying efficacies at different MOR-1 variants. |
| Keywords: | exon; exons; drug efficacy; nonhuman; animal cell; animals; animal tissue; reverse transcription polymerase chain reaction; drug potency; animalia; molecular cloning; cloning, molecular; brain; reverse transcriptase polymerase chain reaction; nucleotide sequence; substrate specificity; rat; alternative splicing; alternative rna splicing; rats; receptor affinity; morphine; sequence homology; blotting, northern; protein variant; mu opiate receptor; receptor gene; receptors, opioid, mu; receptor binding; complementary dna; northern blotting; gene transfer techniques; opioid receptor; cho cells; cricetinae; binding, competitive; guanosine 5'-o-(3-thiotriphosphate); binding assay; mor-1; narcotics; guanosine 5' o (3 thiotriphosphate); mop; priority journal; article; gtpgammas |
| Journal Title: | Journal of Neurochemistry |
| Volume: | 91 |
| Issue: | 4 |
| ISSN: | 0022-3042 |
| Publisher: | Wiley Blackwell |
| Date Published: | 2004-11-01 |
| Start Page: | 881 |
| End Page: | 890 |
| Language: | English |
| DOI: | 10.1111/j.1471-4159.2004.02767.x |
| PROVIDER: | scopus |
| PUBMED: | 15525342 |
| DOI/URL: | |
| Notes: | J. Neurochem. -- Cited By (since 1996):44 -- Export Date: 16 June 2014 -- CODEN: JONRA -- Molecular Sequence Numbers: GENBANK: AY225402, AY225403, AY309000, AY309002; -- Source: Scopus |
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