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Acute desensitization of nociceptin/orphanin FQ inhibition of voltage‐gated calcium channels in freshly dissociated hippocampal neurons
Author(s) -
Pu Lu,
Bao GuoBin,
Ma Lan,
Pei Gang
Publication year - 1999
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.1460-9568.1999.00776.x
Subject(s) - nociceptin receptor , chemistry , agonist , protein kinase c , voltage dependent calcium channel , calcium channel , gabab receptor , hippocampal formation , calcium , pharmacology , biophysics , endocrinology , medicine , receptor , biochemistry , opioid peptide , opioid , biology , kinase , organic chemistry
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, [Phe 1 ‐ψ(CH 2 ‐NH)‐Gly 2 ]nociceptin (1‐13)‐NH 2 , and the EC 50 of the N/OFQ inhibition was ∼ 10 n m , 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 GABA B (γ‐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.