Assessment of delta-opioid receptor activation by a series of peptides in cultured cells.
This study was designed to investigate the relative ability of a series of cyclic opioid peptides to initiate the first activation steps following their binding of delta-opioid receptors. The extent of stimulation of low Km guanosine-triphosphatase (GTPase activity) and inhibition of hormonally-stimulated cAMP accumulation in the NG108-15 (neuroblastoma-glioma) hybrid cell line were determined and compared for six closely related peptides. In addition, their binding affinity was assessed by competition with 3H-[D-Pen2D-Pen5]-enkephalin (3H-DPDPE) in membranes from these cells. All peptides tested elicited comparable maximal effects for both functional responses. Different potencies in stimulating the low Km GTPase was observed at sub-maximal agonist concentrations, although the shallow dose-response behavior did not allow accurate determination of ED50s. Estimation of ED50s for inhibition of cAMP accumulation could be made by curve fitting and were similar for four of these peptides, while DCDPE and 3R-methylDCDPE, the highest affinity analogs, were considerably more potent. In general, the observed differences in hormonal activity somewhat parallel the rank order of binding affinities, but no strict relationship was found between receptor binding and activation.
Costa
E M
EM
Molecular Research Institute, Stanford University, Palo Alto, CA.
Hoffman
B B
BB
Loew
G H
GH
D000595:Amino Acid Sequence; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004723:Endorphins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D005910:Glioma; D006822:Hybrid Cells; D008969:Molecular Sequence Data; D009447:Neuroblastoma; D011487:Protein Conformation; D017465:Receptors, Opioid, delta / Q000187:drug effects / Q000502:physiology*; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured
D004723:Endorphins; D004745:Enkephalins; D017465:Receptors, Opioid, delta; D020881:Enkephalin, D-Penicillamine (2,5)-; D000242:Cyclic AMP; D020558:GTP Phosphohydrolases