Modulation of Ca2+ channels by heterologously expressed wild-type and mutant human μ-opioid receptors (hMORs) containing the A118G single-nucleotide polymorphism

Wojciech Margas, Ira Zubkoff, H. Gregg Schuler, Piotr K. Janicki, Victor Ruiz-Velasco

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

The most common single-nucleotide polymorphism (SNP) of the human μ-opioid receptor (hMOR) gene occurs at position 118 (A118G) and results in substitution of asparagine to aspartate at the N-terminus. The purpose of the present study was to compare the pharmacological profile of several opioid agonists to heterologously expressed hMOR and N-type Ca2+ channels in sympathetic neurons. cDNA constructs coding for wild-type and mutant hMOR were microinjected in rat superior cervical ganglion neurons and N-type Ca 2+ channel modulation was investigated using the whole cell variant of the patch-clamp technique. Concentration-response relationships were generated with the following selective MOR agonists: DAMGO, morphine, morphine-6-glucuronide (M-6-G), and endomorphin I. The estimated maximal inhibition for the agonists ranged from 52 to 64% for neurons expressing either hMOR subtype. The rank order of potencies for estimated EC50 values (nM) in cells expressing wild-type hMOR was: DAMGO (31) ≫ morphine (76) ≅ M-6-G (77) ≅ endomorphin I (86). On the other hand, the rank order in mutant-expressing neurons was: DAMGO (14) ≫ morphine (39) ≫ endomorphin I (74) ≅ M-6-G (82), with a twofold leftward shift for both DAMGO and morphine. The DAMGO-mediated Ca2+ current inhibition was abolished by the selective MOR blocker, CTAP, and by pertussis toxin pretreatment of neurons expressing either hMOR subtype. These results suggest that the A118G variant MOR exhibits an altered signal transduction pathway and may help explain the variability of responses to opiates observed with carriers of the mutant allele.

Original languageEnglish (US)
Pages (from-to)1058-1067
Number of pages10
JournalJournal of neurophysiology
Volume97
Issue number2
DOIs
StatePublished - Feb 1 2007

All Science Journal Classification (ASJC) codes

  • Neuroscience(all)
  • Physiology

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