title: Acute desensitization of nociceptin/orphanin FQ inhibition of voltage-gated calcium channels in freshly dissociated hippocampal neurons.
abstract: Nociceptin/orphanin FQ (N/OFQ), an endogenous ligand for opioid receptor-like receptor, has been shown to inhibit high-voltage-gated calcium channels (VGCCs) in acutely dissociated rat hippocampal pyramidal cells [Knoflach, F., Reinscheid, R.K., Civelli, O. & Kemp, J.A. (1996), J. Neurosci., 16, 6657]. In this study, it was further demonstrated that N/OFQ inhibition of calcium channel current was blocked by its specific antagonist PGN, [Phe1-psi(CH2-NH)-Gly2]nociceptin (1-13)-NH2, and the EC50 of the N/OFQ inhibition was approximately 10 nM, indicating that this effect was really mediated via the opioid receptor-like receptor. The N/OFQ inhibition of the calcium channel current was significantly reduced, as the maximal inhibition decreased from 36 to 23%, by 1-min pretreatment of freshly dissociated hippocampal neurons with the same peptide. The inhibition completely recovered from this acute desensitization in less than 20 min. The N/OFQ inhibition was also greatly attenuated by pretreatment of the neurons with the GABAB (gamma-aminobutyric acid) agonist baclofen while the baclofen inhibition of the calcium channel current was significantly reduced by N/OFQ pretreatment, revealing the agonist-induced desensitization was heterologous in nature. This desensitization was blocked by pretreating the neurons with the sodium channel blocker, tetrodotoxin (TTX), or by removing the extracellular calcium, which indicates the necessity of membrane depolarization and extracellular calcium influx in the process. Furthermore, pretreatment of the neurons with the protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), attenuated the N/OFQ inhibition of the calcium channel current whereas the cAMP-dependent kinase A activator, forskolin, showed no effect, suggesting the probable involvement of PKC in the N/OFQ-induced desensitization.
authors.affiliation: Shanghai Institute of Cell Biology, Shanghai Research Center of Life Sciences, Chinese Academy of Sciences, People's Republic of China.
authors.forename: L
authors.initials: L
authors.lastname: Pu
authors.forename: G B
authors.initials: GB
authors.lastname: Bao
authors.forename: L
authors.initials: L
authors.lastname: Ma
authors.forename: G
authors.initials: G
authors.lastname: Pei
mesh_terms: D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D001464:Barium / Q000493:pharmacokinetics; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020865:Calcium Channels, P-Type / Q000502:physiology*; D002273:Carcinogens / Q000494:pharmacology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D004594:Electrophysiology; D005110:Extracellular Space / Q000737:chemistry; D018755:GABA Agonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018847:Opioid Peptides / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D017966:Pyramidal Cells / Q000737:chemistry* / Q000166:cytology / Q000201:enzymology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D000097629:Nociceptin
chemical_list: D001418:Baclofen; D001464:Barium; D002118:Calcium; D002121:Calcium Channel Blockers; D020865:Calcium Channels, P-Type; D002273:Carcinogens; D005576:Colforsin; D018755:GABA Agonists; D018847:Opioid Peptides; D010446:Peptide Fragments; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D013779:Tetrodotoxin; D000097629:Nociceptin; C114149:nociceptin (1-13)-NH2, Phe(1)-psi(CH2-NH)-Gly(2)-