Characterization of binding kinetics of [3H]Tyr-D-Arg2-Phe-Sar4 at opioid receptors.
The dermorphin-derived, MOP receptor-selective tetrapeptide Tyr-D-Arg2-Phe-Sar4 (TAPS) exhibits a high antinociceptive potency and stimulates respiration in rats. The receptor binding kinetics of [3H]TAPS were investigated using crude calf thalamic membrane preparations. Saturation studies showed binding of [3H]TAPS at two binding sites (0.4 and 3.2 nM). In the presence of MgSO4, [3H]TAPS binding occurred with high affinity at a single site only. The high-affinity binding component was reduced following the addition of K2-EDTA. The increase of the apparent dissociation constant was due to an enhanced dissociation rate (P<0.05), while association rates remained unchanged. Addition of 5'-guanylylimidodiphosphate (Gpp(NH)p) resulted in a reduction of affinity which was augmented in the presence of Na+. Thus, [3H]TAPS, depending on the presence of divalent cations, serves as ligand at two MOP receptor binding sites in the calf thalamus, which may represent distinct affinity states of the same receptor or receptor subtypes thereof.
Vonhof
Stefan
S
Department of Cardiology and Pneumology, Georg-August-University, Robert-Koch-Str. 40, 37075 Göttingen, Germany. svonhof@gwdg.de
Feuerstein
Giora
G
Sirén
Anna-Leena
AL
D000818:Animals; D001665:Binding Sites; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009842:Oligopeptides / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D011957:Receptors, Opioid / Q000378:metabolism*; D013696:Temperature; D013788:Thalamus / Q000166:cytology / Q000378:metabolism; D013997:Time Factors
D009842:Oligopeptides; D011957:Receptors, Opioid; C053418:tyrosyl-arginyl-phenylalanyl-sarcosine