title: Antagonizing effect of protein kinase C activation on the mu-opioid agonist-induced inhibition of high voltage-activated calcium current in rat periaqueductal gray neuron.
abstract: Opioids have been thought to induce analgesia by activating the descending pain control system, especially at the level of periaqueductal gray, and regulate the neurotransmitter release through the inhibition of calcium channel. In the present study, the modulatory effects of protein kinase C and protein kinase A on the mu-opioid agonist-induced inhibition of the high-voltage activated calcium current were examined in the acutely dissociated rat periaqueductal gray neurons with the nystatin-perforated patch-clamp technique. Among 505 neurons tested, the barium current passing through the high-voltage activated calcium channels of 172 neurons (34%) were inhibited by 32+/-3% with the application of an mu-opioid agonist, [D-Ala(2),N-MePhe(4),Gly(5)-ol]-enkephalin (DAMGO, 1 microM). The barium currents itself and the DAMGO-induced inhibitory effects were not affected by the application of either an adenylate cyclase activator (forskolin, 1 microM) or a protein kinase inhibitor (staurosporin, 10 nM) for 2 min. The DAMGO inhibition was completely and irreversibly antagonized by the application of a protein kinase C activator, phorbol-12-myristate-13-acetate (PMA, 1 microM) for 2 min without any alteration of the barium current itself. However, the antagonizing effect of PMA was completely abolished by the application of 10 nM staurosporin for 2 min. After then, PMA did not show the antagonizing effect any more. Inversely, when staurosporin was applied before PMA, the antagonizing effect of PMA was also not shown. These results demonstrate that the mu-opioid agonist-induced inhibition of the periaqueductal gray neuronal high-voltage activated calcium current can be antagonized by protein kinase C activation. This finding may provide us a significant clue to understand the action mechanism of opioid-induced analgesia in the periaqueductal gray.
authors.affiliation: Department of Physiology, College of Medicine, Kyung Hee University, Seoul 130-701, South Korea. ywcho@khu.ac.kr
authors.forename: Y W
authors.initials: YW
authors.lastname: Cho
authors.forename: S H
authors.initials: SH
authors.lastname: Han
authors.forename: B I
authors.initials: BI
authors.lastname: Min
authors.forename: J S
authors.initials: JS
authors.lastname: Rhee
authors.forename: N
authors.initials: N
authors.lastname: Akaike
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002273:Carcinogens / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010146:Pain / Q000378:metabolism* / Q000503:physiopathology; D010487:Periaqueductal Gray / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000701:Analgesics, Opioid; D015220:Calcium Channels; D002273:Carcinogens; D004791:Enzyme Inhibitors; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D005576:Colforsin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate