The Japanese Journal of Pharmacology
Online ISSN : 1347-3506
Print ISSN : 0021-5198
ISSN-L : 0021-5198
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Recent Advances in the Search for the μ-Opioidergic System
Differential Mechanism of G-Protein Activation Induced by Endogenous μ-Opioid Peptides, Endomorphin and β-Endorphin
Hirokazu MizoguchiLeon F. TsengTsutomu SuzukiIchiro SoraMinoru Narita
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2002 Volume 89 Issue 3 Pages 229-234

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Abstract

It is well documented that the μ-opioid receptor (MOP-R) is expressed by neurons in several central nervous system regions. Its occupancy with agonist drugs modulate a variety of physiological processes including pain, reward, stress, immune responses, neuroendocrine functions, and cardiovascular control. Based on the receptor binding assay, endomorphin-1 and endomorphin-2 have the highest specificity and affinity for the MOP-R of any endogenous substance so far described in the mammalian nervous system. In contrast, β-endorphin exhibits the strongest actions among endogenous opioid peptides mainly through the MOP-R; however, it also shows the distinct pharmacological actions. Recent cloning and expression studies have indicated that MOP-Rs are seven-transmembrane domain receptors whose actions are mediated through activation of heterotrimeric guanine nucleotide binding proteins (G-proteins). The activation of G-proteins by MOP-Rs can be measured by assessing agonist-induced stimulation of membrane binding of guanosine-5'-o-(3-[35S]thio)triphosphate ([35S]GTPγS). The subject of the present review is to focus on the differential mechanism underlying G-protein activation induced by these μ-opioid peptides using the [35S]GTPγS binding assay.

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© The Japanese Pharmacological Society 2002
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