title: Activation of protein kinase C antagonizes the opioid inhibition of calcium current in rat spinal dorsal horn neurons.
abstract: Spinal dorsal horn (SDH) is one of important regions in both nociceptive transmission and antinociception. Opioid peptides produce analgesia via regulation of neurotransmitter release through modulation of voltage-dependent Ca(2+) channel (VDCC) in neuronal tissues. The modulatory effect of micro-opioid receptor (MOR) activation on VDCC was investigated in acutely isolated rat SDH neurons under the conventional whole-cell patch-clamp recording mode. The Ba(2+) current passing through VDCC was reversibly inhibited by a MOR agonist, [D-Ala(2),N-MePhe(4),Gly(5)-ol]-enkephalin (DAMGO, 1 microM). Among 108 SDH neurons tested, VDCC of 39 neurons (36%) were inhibited by MOR activation, while other 69 neurons (64%) were not affected. The L-, N-, P/Q-, and R-type VDCC components shared 58.4+/-18.9%, 29.3+/-12.1%, 8.7+/-7.2%, and 3.4+/-4.8% of the total VDCC, respectively. Among VDCC subtypes inhibited by MOR activation, L- and N-types were 61.4+/-12.8% and 30.7+/-14.4%, respectively, while both P/Q- and R-types were 7.9+/-11.8%. A depolarizing pre-pulse increased the amplitude of VDCC and suppressed most of the inhibitory effect of MOR activation. Application of 1 microM phorbol-12-myristate-13-acetate completely antagonized the inhibitory effect of MOR activation without any alteration of basal VDCC amplitude. In contrast, the response of MOR activation was not altered by application of 4-alpha-phorbol (1 microM), 2-[3-Dimethylaminopropyl]indol-3-yl]-3-(indol-3-yl) maleimide (GF109203X, 1 microM), forskolin (1 microM), N-(2-[p-Bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide hydrochloride (H-89, 1 microM). These results indicate that activation of MOR coupled to G-proteins inhibits VDCC, and that this G-protein-mediated inhibition is antagonized by PKC-dependent phosphorylation.
authors.affiliation: Department of Physiology, College of Medicine, Kyung Hee University, 1 Hoigi-dong, Dongdaemoon-gu, Seoul 130-701, South Korea.
authors.forename: Jong-Ju
authors.initials: JJ
authors.lastname: Lee
authors.forename: Eu-Teum
authors.initials: ET
authors.lastname: Hahm
authors.forename: Byung-Il
authors.initials: BI
authors.lastname: Min
authors.forename: Young-Wuk
authors.initials: YW
authors.lastname: Cho
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D004347:Drug Interactions; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D007211:Indoles / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D008301:Maleimides / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009294:Narcotics / Q000494:pharmacology*; D018408:Patch-Clamp Techniques / Q000379:methods; D020671:Posterior Horn Cells / Q000187:drug effects* / Q000502:physiology*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013449:Sulfonamides; D013755:Tetradecanoylphorbol Acetate / Q000031:analogs & derivatives* / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D000701:Analgesics, Opioid; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D007211:Indoles; D007546:Isoquinolines; D008301:Maleimides; D009294:Narcotics; D026902:Potassium Channel Blockers; D013449:Sulfonamides; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D005576:Colforsin; D013779:Tetrodotoxin; C016658:phorbolol myristate acetate; D019789:Tetraethylammonium; D011493:Protein Kinase C; C070515:bisindolylmaleimide I; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide; D013755:Tetradecanoylphorbol Acetate