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The identification of μ opioid receptors on colonic circular smooth muscle cells
Author(s) -
Hawkins Edward G,
Ross Gracious R,
Gabra Bichoy H,
Dewey William L,
Akbarali Hamid I
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.712.9
Subject(s) - myenteric plexus , morphine , motility , isometric exercise , excitatory postsynaptic potential , inhibitory postsynaptic potential , stimulation , medicine , tonic (physiology) , atropine , endocrinology , receptor , opioid , chemistry , immunohistochemistry , biology , microbiology and biotechnology
Morphine‐induced constipation severely hampers the clinical utility of this excellent pain reliever. Studies of the chronic effects of morphine on gastrointestinal motility have mainly focused on inhibition of both excitatory and inhibitory motor neurons in the myenteric plexus of the ileum. In the present study we examined the direct effects of morphine on colon smooth muscle. Isometric force was measured from colonic circular muscle ring preparations in an organ bath. Morphine (10nM – 1 μM) produced both tonic and rhythmic phasic contractions in the presence of atropine (1 μM). Tolerance did not develop to repeated exposure to morphine. The expression of μreceptor (MOR) was determined by immunohistochemistry using anti‐MOR antibody. In cross‐sections of the colonic wall, MOR was detected in both enteric ganglia and circular muscle. MOR expression was confirmed in enzymatically‐isolated single smooth muscle cells. The specificity of the MOR antibody was further verified in MOR‐expressing CHO cells. These data demonstrate the expression of MOR on smooth muscle cells and suggest that part of morphine's effect on gastrointestinal motility may be due to direct stimulation of circular smooth muscle. In addition to its well known effects on neuronal function, morphine‐induced enhanced non‐propulsive segmental contractions are important in the genesis of constipation. Supported by DK46367, DA01647.