Selective and interactive down-regulation of mu- and delta-opioid receptors in human neuroblastoma SK-N-SH cells.
Human neuroblastoma SK-N-SH cells, which contain both mu- and delta-opioid receptors, were grown under conditions that provided a mu:delta ratio of 1.5:1. Both receptors were down-regulated after 72 hr of exposure to 100 nM etorphine. Selective down-regulation was demonstrated using selective opioid agonists; the mu agonist Tyr-D-Ala2-Gly-(Me)Phe4-Gly-ol down-regulated mu- but not delta-opioid receptors, whereas prolonged exposure to the selective delta agonist D-Pen2,D-Pen5-enkephalin resulted in delta- but not mu-opioid receptor down-regulation. Morphine, which binds mu- as well as delta-opioid receptors, down-regulated both receptor subtypes. NG108-15 cells, which contain delta receptors exclusively, were also tested. NG108-15 cells did not exhibit delta-opioid receptor down-regulation when exposed to morphine. The discrepancy between the effect of chronic morphine treatment on delta receptors in SK-N-SH cells and in NG108-15 cells raised the question of whether the coexistence of mu receptors in the former allowed morphine to down-regulate delta receptors. The role of mu-opioid receptors in morphine-induced delta receptor down-regulation was studied by using the irreversible mu antagonist beta-funaltrexamine. Pretreatment of SK-N-SH cells with beta-funaltrexamine prevented down-regulation of delta receptors in response to chronic exposure to morphine but did not affect down-regulation of delta receptors in response to D-Pen2,D-Pen5-enkephalin. The experimental data indicate that morphine-induced delta-opioid receptor down-regulation is dependent on the presence of functional mu receptors in the same cell.
Baumhaker
Y
Y
Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel-Aviv University, Israel.
Gafni
M
M
Keren
O
O
Sarne
Y
Y
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000700:Analgesics / Q000494:pharmacology*; D015536:Down-Regulation / Q000187:drug effects; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000494:pharmacology; D006801:Humans; D009020:Morphine / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009447:Neuroblastoma / Q000473:pathology; D011759:Pyrrolidines / Q000494:pharmacology; D017465:Receptors, Opioid, delta / Q000187:drug effects* / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000187:drug effects* / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000700:Analgesics; D004745:Enkephalins; D011759:Pyrrolidines; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009271:Naltrexone; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; C024524:beta-funaltrexamine; D009020:Morphine; D020881:Enkephalin, D-Penicillamine (2,5)-