Activation of protein kinase C antagonizes the opioid inhibition of calcium current in rat spinal dorsal horn neurons.
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.
Lee
Jong-Ju
JJ
Department of Physiology, College of Medicine, Kyung Hee University, 1 Hoigi-dong, Dongdaemoon-gu, Seoul 130-701, South Korea.
Hahm
Eu-Teum
ET
Min
Byung-Il
BI
Cho
Young-Wuk
YW
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
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