Abstract
The opioid receptor mediating inhibitory action of morphine in the electrically stimulated guinea pig ileum was irreversibly photoinactivated by morphine epoxide (3 × 10 −6). Morphine epoxide (up to 3 × 10 −5 M) did not influence the responses of rat vas deferens (ϵ-receptor) or rabbit vas deferens (κ-receptor) to electrical stimulation. Effective concentrations of morphine epoxide were much lower in the guinea pig ileum (μ-receptor) than in the mouse vas deference (δ-receptor). The inhibitory action of [Met]-enkephalin on the twitch responses of the rat vas deferens and mouse vas deferens to electrical stimulation were not influenced after irradiation in the presence of morphine epoxide (3 × 10 −6 M). Therefore, morphine epoxide is probably a useful probe for photoaffinity labeling of the μ-receptor in vitro.
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