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Eur J Pharmacol. 1998 Jan 19;342(1):123-6.

Specific G protein activation and mu-opioid receptor internalization caused by morphine, DAMGO and endomorphin I.

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Department of Biopharmaceutical Sciences and Pharmaceutical Chemistry, University of California, San Francisco 94143-0446, USA.


Previous studies have shown that the agonist [D-Ala2, N-Me-Phe4, Gly-ol5]enkephalin (DAMGO) but not morphine induces mu-opioid receptor internalization [Arden, J.R., Segredo, V., Wang, Z., Lameh, J., Sadee, W., 1995. J. Neurochem. 65, 1636-1645]. In the present study we investigated the relationship between internalization of the mu-opioid receptor and the specific G proteins activated following treatment with morphine, DAMGO and endomorphin I (Tyr-Pro-Trp-Phe-NH2) (a putative endogenous mu-opioid receptor agonist) in human embryonic kidney (HEK) cells. Endomorphin I and DAMGO, but not morphine, caused mu-opioid receptor internalization. Morphine, DAMGO and endomorphin I each activated Gi1 alpha/Gi2 alpha, Go alpha and Gi3 alpha to a similar extent, but not Gq alpha/G11 alpha or Gs alpha in HEK membranes. Therefore, the three ligands tested differed in their ability to internalize mu-opioid receptors even though they were similar in activating individual G proteins.

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