[¹²⁵I]Orphanin FQ/nociceptin binding in Raji cells

Western blots using an antibody which recognizes the orphanin FQ/ nociceptin (OFQ/N) receptor reveals a band at approximately 69 kD in several cell lines, including the Raji human B cell lymphoma cell line. RT-PCR confirms the presence of this receptor in the Raji cells. Binding studies revealed a high affinity [¹²⁵I][Tyr¹⁴]OFQ/N site in the Raji cells. The affinity of [¹²⁵I] [Tyr¹⁴]OFQ/N in the Raji cells (K(D) 68.4 pM) was similar to that in the transfected receptor (K(D) 36.7 pM). Its selectivity profile also was quite similar. OFQ/N competed binding quite potently (K(i) 65 pM), as did [Tyr¹⁴]OFQ/N (K(i) 33 pM). Traditional opioids displayed no appreciable affinity for the binding at any concentration examined, with the exception of naloxone benzoylhydrazone, which had only a very modest affinity. The receptors in the Raji cells were functionally active. OFQ/N inhibited forskolin-stimulated cyclase by 72% with an IC₅₀ value of approximately 1 nM.