Endogenous opioid receptor-like receptor in human neuroblastoma SK-N-SH cells: Activation of inhibitory G protein and homologous desensitization

ENDOGENOUS expression of opioid receptor-like receptor (ORL1) in human neuroblastoma SK-N-SH cells was demonstrated by binding with nociceptin/orphanin FQ (N/OFQ). Scatchard analysis of [H-3]N/OFQ saturation binding data gave K-d = 1.3 +/- 0.1 nM and B-max = 158 +/- 2.5 fmol/mg protein. N/OFQ stimulation increased [S-35]GTP gamma S binding to cell membranes and attenuated forskolin-induced cAMP accumulation in a concentration-dependent manner. The effects of N/OFQ were eliminated by the pretreatment of pertussis toxin (PTX) but not by the antagonists of opioid receptors, revealing mediation of N/OFQ signal transduction by ORL, receptor and PTX sensitive G protein(s). The ability of N/OFQ to inhibit cAMP production greatly reduced after prechallenging with N/OFQ, eating that ORL, undergoes homologous desensitization in neuronal cells.