Chronic opioid antagonist treatment selectively regulates trafficking and signaling proteins in mouse spinal cord.
Chronic opioid antagonist treatment produces functional supersensitivity and mu-opioid receptor (muOR) upregulation. Studies suggest a role for G-protein receptor kinases (GRKs) and dynamin (DYN), but not signaling proteins (e.g., G(ialpha2)), in regulation of muOR density following opioid treatment. Therefore, this study examined muOR density, agonist potency, and the abundance and gene expression of GRK-2, DYN-2, and G(ialpha2) in mouse spinal cord after opioid antagonist treatment. Mice were implanted with a 15 mg naltrexone (NTX) or placebo pellet and 8 days later pellets were removed. At 24 and 192 h following NTX treatment, mice were tested for spinal DAMGO analgesia. Other mice were sacrificed at 0 or 192 h following NTX treatment and G(ialpha2), GRK-2, and DYN-2 protein and mRNA levels determined. [(3)H] DAMGO binding studies were also conducted. Immediately following NTX treatment (0 h), muOR density was increased (+ approximately 135%), while 192 h following NTX treatment muOR density was unchanged. NTX increased DAMGO analgesic potency (3.1-fold) 24 h following NTX treatment, while there was no effect at 192 h. NTX decreased protein and mRNA abundance of GRK-2 (-32%; -48%) and DYN-2 (-25%; -29%) in spinal cord at 0 h. At 192 h following 8-day NTX treatment, GRK-2 protein and mRNA were at control levels, while DYN-2 protein remained decreased (-31%) even though DYN-2 mRNA had returned to control levels. G(ialpha2) was unaffected by NTX treatment. These data suggest that opioid antagonist-induced mu-receptor upregulation is mediated by changes in abundance and gene expression of proteins implicated in receptor trafficking, which may decrease constitutive receptor cycling.
Patel
Chintan N
CN
Department of Pharmaceutical Sciences, St. John's University, Queens, New York 11439, USA.
Rajashekara
Vikram
V
Patel
Kaushal
K
Purohit
Vishal
V
Yoburn
Byron C
BC
D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D034285:Dynamin II / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D008297:Male; D051379:Mice; D009271:Naltrexone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000187:drug effects / Q000378:metabolism; D013116:Spinal Cord / Q000187:drug effects* / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics; D051552:beta-Adrenergic Receptor Kinases
D009292:Narcotic Antagonists; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D017450:Receptors, Opioid, mu; D009271:Naltrexone; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C498016:Gnai2 protein, mouse; D034285:Dynamin II