Ca2+ channel and adenylyl cyclase modulation by cloned μ-opioid receptors in GH3 cells

E. T. Piros, P. L. Prather, H. H. Loh, P. Y. Law, C. J. Evans, T. G. Hales

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88 Scopus citations


Members of the three classes of opioid receptors (μ, δ, and κ) have been cloned and characterized in unexcitable cell lines using biochemical techniques. However, an important function of these cloned receptors, their coupling to voltage-activated Ca2+ channels, remains untested. We stably transfected cloned rat μ-opioid receptor cDNAs into clonal pituitary GH3 cells. GH3 cells expressing μ-opioid receptors (GH3MOR cells) bound the receptor-specific ligands [D-Ala2,Me-Phe4,Gly-ol5]-enkephalin (DAMGO) and morphine with high affinity (Ki = 1.0 and 7.2 nM, respectively), and these ligands also potently inhibited adenylyl cyclase activity (IC50 = 21.9 and 55.2 nM, respectively). Functional coupling of μ-opioid receptors to voltage-activated Ca2+ channels was compared with that of endogenous somatostatin (SRIF) receptors in GH3MOR cells, using the patch-clamp technique, with Ba2+ as the charge carrier. DAMGO (1 μM) and SRIF (1 μM) inhibited Ba2+ currents by 23.8 ± 1.0% and 22.9 ± 2.5%, respectively. DAMGO (0.1 nM to 10 μM) dose-dependently inhibited Ba2+ currents, with an IC50 of 105 nM. The μ-opioid receptor agonist morphine (1 μM) inhibited currents by 13.5 ± 1.1% and the δ-opioid receptor-selective ligand [D-Pen2,5]-enkephalin (1 μM) caused only 3.5 ± 2.1% inhibition. The inhibitory actions of DAMGO, morphine, and [D-Pen2,5]-enkephalin were reversed by naloxone. Ba2+ current inhibitions by DAMGO and SRIF were attenuated by pertussis toxin pretreatment. Nimodipine reduced the amplitude of Ba2+ current inhibition by DAMGO, suggesting that μ-opioid receptors couple to L-type Ca2+ channels in GH3MOR cells.

Original languageEnglish (US)
Pages (from-to)1041-1049
Number of pages9
JournalMolecular Pharmacology
Issue number5
StatePublished - May 1995


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