Biochemical characterization of high-affinity 3H-opioid binding. Further evidence for Mu1 sites.
In saturation studies with [3H]dihydromorphine, unlabeled D-Ala2-D-Leu5-enkephalin (1 nM) inhibited the high-affinity binding component far more potently than the lower-affinity one. Similarly, morphine (1 nM) inhibited the higher-affinity binding of 3H-D-Ala2-D-Leu5-enkephalin to a greater extent than its lower-affinity binding component, consistent with a common high-affinity binding site for opiates and enkephalins. Treatment of tissue with either trypsin (1 microgram/ml) or N-ethylmaleimide (25 microM) effectively eliminated the high-affinity binding component of a series of 3H-opiates and opioid peptides. Competition studies following both treatments were consistent with a common high-affinity binding site. Both treatments also eliminated the ability of low morphine concentrations (less than 1 nM) to inhibit 3H-D-Ala2-D-Leu5-enkephalin binding and of low D-Ala2-D-Leu5-enkephalin concentrations (less than 1 nM) to inhibit [3H]dihydromorphine binding. Protection experiments examining N-ethylmaleimide (25 microM) inhibition of [3H]dihydromorphine binding showed significant protection (p less than 0.002) by both unlabeled D-Ala2-D-Leu5-enkephalin and morphine (both at 1 nM). When studied together, both naloxonazine and N-ethylmaleimide inhibited [3H]dihydromorphine binding to a similar extent. Equally important, tissue previously treated with naloxonazine was far less sensitive to N-ethylmaleimide than was untreated control tissue, consistent with the possibility that both treatments affected the same site. Together, these results support the concept of a common high-affinity binding site for opiates and opioid peptides.
D000818:Animals; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004090:Dihydromorphine / Q000378:metabolism*; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D016308:Enkephalin, Leucine-2-Alanine; D005033:Ethylmaleimide / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009022:Morphine Derivatives / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism*; D017450:Receptors, Opioid, mu; D014316:Tritium; D014357:Trypsin / Q000494:pharmacology
D009022:Morphine Derivatives; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D014316:Tritium; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine; D009020:Morphine; D004090:Dihydromorphine; D014357:Trypsin; D005033:Ethylmaleimide