[H-3] [D-PEN2, D-PEN5]ENKEPHALIN BINDING TO DELTA-OPIOID RECEPTORS ON INTACT NEUROBLASTOMA-GLIOMA (NG 108-15) HYBRID-CELLS

[3H][D-Pen2, D-Pen5]enkephalin binding to intact NG 108-15 cells has been measured under physiological conditions of temperature and medium. The dissociation constant (7.78 nM), receptor density (385 fmol/mg protein), and Hill slope (1.06) values measured under these conditions are consistent with values obtained by others using membranes prepared from these cells. Kinetic analysis of the radioligand binding to these cells show biphasic association and monophasic dissociation processes suggesting the presence of different receptor affinity states for the agonist. The data show that the binding affinity of [3H][D-Pen2, D-Pen5]enkephalin under physiological conditions is not substantially different to that measured in 50 mM Tris buffer using cell membrane fractions. Unlike DPDPE, the μ opioid agonists morphine, normorphine, PL-17, and DAMGO, have much lower affinity for the δ receptor measured under these conditions than is observed by studies using 50 mM Tris buffer. The results described here suggest that this assay may serve as a useful model of δ opioid receptor binding in vivo. © 1990.