Journal
BRAIN RESEARCH
Volume 1028, Issue 2, Pages 121-132Publisher
ELSEVIER
DOI: 10.1016/j.brainres.2004.07.055
Keywords
endocytosis; hypertonic; opioid receptor; sucrose; tolerance
Categories
Funding
- NIDA NIH HHS [DA05907, DA011655] Funding Source: Medline
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The human neuroblastoma cell line, SH-SY5Y, was used to examine the effects of morphine and the endogenous opioid peptides, endomorphin-1 (EM-1) and endomorphin-2 (EM-2), on mu opioid receptor (MOR) internalization and down-regulation. Treatment for 24 h withEM-1, EM-2 ormorphine at 100 nM, 1 muM and 10 muM resulted in a dose-dependent down-regulation of mu receptors. Exposure of cells to 10 muM EM-1 for 2.5, 5 and 24 h resulted in a time-dependent down-regulation of mu receptors. Down-regulation of mu receptors by morphine and EM-1 was blocked by treatment with hypertonic sucrose, c onsistent with an endocytosis-dependent mechanism. Sensitive cell-surface binding studies with a radiolabeled mu antagonist revealed that morphine was able to induce internalization of mu receptors naturally expressed in SH-SY5Y cells. EM-1 produced a more rapid intemalization of mu receptors than morphine, but hypertonic sucrose blocked the internalization induced by each of these agonists. This study demonstrates that, like morphine, the endomorphins down-regulate mu opioid receptors in a dose- and time-dependent manner. This study also demonstrates that morphine, as well as EM-1, can induce rapid, endocytosisdependent internalization of mu opioid receptors in SH-SY5Y cells. These results may help elucidate the ability of mu agonists to regulate the number and responsiveness of their receptors. Published by Elsevier B.V.
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