AJP - Gastrointestinal and Liver Physiology, Vol 260, Issue 1 103-G107, Copyright © 1991 by American Physiological Society

ARTICLES

Identification of opioid receptors on gastric muscle cells by selective receptor protection

J. R. Grider and G. M. Makhlouf
Department of Physiology, Medical College of Virginia, Richmond 23298-0711.

Opioid receptors on isolated gastric smooth muscle cells were characterized pharmacologically by a technique in which synthetic selective opioid agonists and antagonists were used to protect and thus enrich a specific receptor type while all other receptors were inactivated by N-ethylamaleimide. Treatment of the cells with the selective mu-receptor agonist DAGO or antagonist CTAP preserved only the response to DAGO; treatment with the selective delta-receptor agonist DPDPE or antagonist naltrindole preserved only the response to DPPE; and treatment with the selective kappa-receptor agonist U50,488H or antagonist nor-binaltorphimine preserved only the response to U50,488H. The results established the presence of distinct kappa-, delta-, and mu-opioid receptors capable of mediating contraction of isolated gastric muscle cells. The pattern of interaction of endogenous opioid peptides with protected receptors implied that dynorphin-(1-13) and Met-enkephalin were selective agonists for kappa- and delta-opioid receptors, respectively, and Leu-enkephalin a preferential agonist of mu-opioid receptors. The results were confirmed by a reverse approach in which opioid receptors were inactivated by site-directed irreversible antagonists. beta-Funaltrexamine, a mu-selective antagonist, abolished the response to mu-receptor agonists, whereas beta-chlornaltrexamine, a mu- and kappa-selective antagonist, abolished the response to mu-receptor agonists and partially inhibited the response to kappa-receptor agonists.

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