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Effects of receptor density on Nociceptin/OrphaninFQ peptide receptor desensitisation: studies using the ecdysone

T A Barnes1, J McDonald, D J Rowbotham

  • 1Department of Cardiovascular Sciences (Pharmacology and Therapeutics Group), Division of Anaesthesia, Critical Care and Pain Management, University of Leicester, Leicester Royal Infirmary, Leicester LE1 5WW, UK.

Naunyn-Schmiedeberg'S Archives of Pharmacology
|September 28, 2007
PubMed

Insights

Pretreatment with nociceptin/orphaninFQ (N/OFQ) reduces nociceptin receptor (NOP) density and function. This study investigated N/OFQ

Area of Science:

  • Pharmacology
  • Neuroscience
  • Molecular Biology

Background:

  • G-protein coupled receptors like the nociceptin receptor (NOP) are crucial in pain signaling.
  • Desensitization of NOP receptors by their ligand, nociceptin/orphaninFQ (N/OFQ), is known, but receptor expression and genomic effects remain unclear.
  • Understanding these mechanisms is vital for developing targeted pain therapies.

Purpose of the Study:

  • To investigate the effects of N/OFQ pretreatment on NOP receptor density, GTPgamma[35S] binding, cAMP formation, and NOP mRNA levels.
  • To utilize an ecdysone-inducible NOP expression system (CHO INDhNOP) for controlled receptor expression.
  • To elucidate the molecular mechanisms underlying NOP receptor desensitization.

Main Methods:

  • Established a Chinese Hamster Ovary (CHO) cell line with inducible NOP receptor expression (CHO INDhNOP).
  • Induced NOP expression using varying concentrations of Ponasterone A (PonA) and pretreated cells with N/OFQ.
  • Assessed receptor density (Bmax), binding affinity, GTPgamma[35S] binding, cAMP inhibition, and NOP mRNA levels.

Main Results:

  • N/OFQ pretreatment significantly reduced NOP receptor density (Bmax) and GTPgamma[35S] binding potency and efficacy.
  • A reduction in potency for N/OFQ-mediated cAMP inhibition was observed, without affecting efficacy.
  • NOP mRNA levels decreased following N/OFQ pretreatment, particularly when measured concurrently with PonA induction.

Conclusions:

  • N/OFQ pretreatment leads to a decrease in cell surface NOP receptor numbers and impaired functional coupling.
  • The observed desensitization occurs at both pseudo-physiological and supraphysiological receptor densities.
  • Further research is required to fully understand the genomic effects and optimal desensitization protocols.

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