Effect of agmatine on DAMGO-induced mu-opioid receptor down-regulation and internalization via activation of IRAS, a candidate for imidazoline I(1) receptor.
Agmatine, an endogenous ligand for imidazoline I(1) receptor, has previously been shown to prevent opioid tolerance in rats and mice, but the cellular mechanisms remain unknown. In the present study, the effects of agmatine activation on imidazoline I(1) receptor on the desensitization, down-regulation and internalization of micro opioid receptor were investigated. Two cell lines, CHO cells transfected micro opioid receptor (CHO-micro cells) and co-transfected micro opioid receptor and imidazoline I(1) receptor antisera-selected protein (IRAS) (CHO-micro/IRAS cells), were used. In both CHO-micro cells and CHO-micro/IRAS cells, agmatine (0.01-10 microM) did not affect the desensitization of micro opioid receptor induced by [d-Ala(2), N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO) (10 microM) treatment for 30 min. However, agmatine (0.1-100 nM) co-pretreatment with DAMGO (1 microM) for 12 h concentration-dependently inhibited DAMGO-induced down-regulation of micro opioid receptor in CHO-micro/IRAS cells, but not in CHO-micro cells. Efaroxan, the I(1)/alpha(2)-adrenoceptors mix antagonist, completely reversed the inhibitory effect of agmatine, suggesting the participation of imidazoline I(1) receptor. In addition, agmatine (1-100 nM) inhibited DAMGO-induced internalization of micro opioid receptor in CHO-micro/IRAS cells, which was reversed by efaroxan as well. While treatment with DAMGO (1 microM) or co-treatment with agmatine (1-100 nM) for 12 h failed to affect the mRNA level of micro opioid receptor. Taken together, these results indicate that the inhibitory effect of agmatine on tolerance in vitro might be related to attenuation of the internalization and down-regulation of micro opioid receptor via activation of imidazoline I(1) receptor.
Beijing Institute of Pharmacology and Toxicology, 27th Taiping Road, Beijing 100850, China.
Yan
Y
Gao
Fei
F
Li
Ning
N
Wu
Rui-Bin
RB
Su
Ying
Y
Liu
Xin-Qiang
XQ
Lu
Yin
Y
Liu
Jin
J
Li
D000376:Agmatine / Q000008:administration & dosage / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004361:Drug Tolerance / Q000502:physiology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology*; D054755:Imidazoline Receptors / Q000187:drug effects* / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000187:drug effects* / Q000378:metabolism; D014162:Transfection
D054755:Imidazoline Receptors; D047908:Intracellular Signaling Peptides and Proteins; C458505:NISCH protein, human; D012333:RNA, Messenger; D017450:Receptors, Opioid, mu; C410887:imidazoline I1 receptors; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D000376:Agmatine