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Alterations in β‐arrestin expression in guinea‐pig ileum and colon following morphine tolerance
Author(s) -
Kang Minho,
Payne Hollis M,
Dewey William L,
Akbarali Hamid I
Publication year - 2010
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.24.1_supplement.583.6
Subject(s) - ileum , morphine , myenteric plexus , medicine , endocrinology , pharmacology , chemistry , biology , immunohistochemistry
Repeated administration of morphine results in the development of tolerance to its antinociceptive effects. We have previously shown that tolerance also occurs to morphine‐induced inhibition of neurogenic contractions in the mouse ileum but not in the colon. The aim of the present study was to examine the development of morphine tolerance in the guinea‐pig ileum and colon and determine the role of G‐protein coupled receptor kinase 2 (GRK2) and β‐arrestin. Isolated guinea‐pig ileum longitudinal muscle‐myenteric plexus (LMMP) and colonic muscle strips were set‐up in the organ bath. Field stimulated contractions were dose‐dependently inhibited by morphine (10nM −10 μM) in both ileum and colon. Incubation with 10 μM morphine for 1 hr induced tolerance to subsequent administration in the ileum but not in the colon. The expression and interaction of GRK2 and β‐arrestin with the μ opioid receptor (MOR) were determined by Western blots. Immunoprecipitation of MOR with GRK2 and β‐arrestin was enhanced after morphine treatment in both tissues. The expression ratio of GRK2/GAPDH was similar, however, that of β‐arrestin/GAPDH was significantly less in the ileum (50 ± 20%) compared to the colon. Morphine treatment (10 μM for 1hr) did not alter the expression levels of GRK2 in either tissues, but markedly reduced β‐arrestin expression by approx. 30% in the ileum. In stably MOR transfected CHO cells, overexpression of GRK2 increased MOR internalization. These studies suggest that an enhanced expression of β‐arrestin in the colon may preclude development of morphine tolerance. Supported by NIH DA024009.