RAPID AGONIST-INDUCED LOSS OF I-125 BETA-ENDORPHIN OPIOID RECEPTOR-SITES IN NG108-15, BUT NOT SK-N-SH NEUROBLASTOMA-CELLS

We have measured mu and delta-opioid receptor sites on intact SK-N-SH and NG108-15 neuroblastoma cells, respectively, in culture. Use of I-125-beta-endorphin (beta-E) as a tracer, together with beta-E(631) to block high-affinity non-opioid binding in both cell lines, permitted the measurement of cell surface-mu and delta-opioid receptor sites. Labeling was at delta-sites in NG108-15 cells and predominantly at mu-sites in SK-N-SH cells. Pretreatment with the mu and delta-agonist, DADLE, caused a rapid loss of cell surface-delta-receptor sites in NG108-15 cells, but failed to reduce significantly mu-receptor density in SK-N-SH cells.