Characterization of [3H]morphine binding to interleukin-1-activated thymocytes.
We have previously reported that interleukin-1-induced proliferation of thymocytes is accompanied by the appearance of [3H]morphine binding sites on these cells. In the present study, we have characterized these binding sites. They differ from classical opioid receptors in the brain in several ways, including: 1) lack of stereoselectivity; 2) relatively low affinity (Kd = 50 nM) and high capacity (Bmax = 3 pmol/mg of protein); 3) binding is strongly inhibited by Ca++, Mg++, Mn++ and Cl- ions and 4) binding is inhibited by proteinase K or E and by phospholipase A2 but not trypsin treatment of thymocyte membranes. The binding sites, which were found largely on the CD4+ subset of T-cells, also showed a preference for opioid alkaloids over peptides. These [3H]morphine binding sites may mediate a negative feedback effect on interleukin-1-induced proliferation of thymocytes in vivo.
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Department of Pharmacology, University of Minnesota Medical School, Minneapolis.
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D000818:Animals; D001665:Binding Sites; D001853:Bone Marrow / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004229:Dithiothreitol; D010450:Endopeptidases; D007375:Interleukin-1 / Q000494:pharmacology*; D008213:Lymphocyte Activation / Q000187:drug effects; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009020:Morphine / Q000378:metabolism*; D010740:Phospholipases; D011957:Receptors, Opioid / Q000378:metabolism; D013816:Thermodynamics; D013950:Thymus Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014316:Tritium
D007375:Interleukin-1; D011957:Receptors, Opioid; D014316:Tritium; D009020:Morphine; D010740:Phospholipases; D010450:Endopeptidases; D004229:Dithiothreitol