Abstract
The effect of the volatile anesthetics (VAs) halothane (0.59 mM) and isoflurane (0.70 mM) on protein kinase C (PKC)-mediated modulation of α1E type of high-voltage-gated Ca2+ channels was examined in Xenopus oocytes coexpressing m1 muscarinic acetylcholine receptors. Phorbol-12-myristate-13-acetate (PMA) or 1,2-dioctanoyl-sn-glycerol (DOG) was used to activate PKC directly, whereas indirect activation was induced with acetyl-β-methylcholine (MCh). The interaction between PKC activators and VAs was examined by perfusing either VA before, during, or after the administration of PMA, DOG, or MCh. In addition, the effect of VAs was studied after the down-regulation of PKC. The application of VAs inhibited Ba2+ current (IBa), whereas PMA (500 nM), DOG (100 μM), or MCh (1 and 10 μM) markedly potentiated IBa. VAs inhibited PMA- or DOG-enhanced IBa to the same extent as seen in controls. The inhibition of IBa induced by VAs was not reversed by PMA or DOG. The administration of VAs in combination with PMA, DOG, or MCh (1 μM) led to the inhibition ofIBa. MCh (10 μM) counteracted the inhibitory effect of VAs when administered together and reversed the inhibition of IBa produced by VAs. These differences in the responses between PMA and MCh (10 μM) may be based on the involvement of various pools of PKC. It is suggested that VAs act directly at the membrane, because they blocked the membrane-based action of PMA, whereas the receptor-based action of MCh was only partially blocked. It is possible that some PKC isoforms may not be a direct target of VAs.
Footnotes
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Send reprint requests to: Dr. Ganesan L. Kamatchi, 1877 Old Med Sch, Department of Anesthesiology, P.O. Box 800710, University of Virginia Health System, Charlottesville, VA 22908-0710. E-mail:gk3p{at}virginia.edu
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↵1 This work was supported by National Institutes of Health Grants R29-GM52387 (M.E.D.) and GM31144 (C.L.).
- Abbreviations:
- VA
- volatile anesthetic
- PMA
- phorbol-12-myristate-13-acetate
- 4α-PDDC
- 4α-phorbol-12,13-didecanoate
- MCh
- acetyl-β-methylcholine
- PKC
- protein kinase C
- cPKC
- conventional PKC
- IBa
- Ba2+ current
- DOG
- 1,2-dioctanoyl-sn-glycerol
- DAG
- diacylglycerol
- HAL
- halothane
- ISO
- isoflurane
- IP3
- inositol-1,4,5-triphosphate
- HVGCC
- high-voltage-gated calcium channel
- Received November 3, 1999.
- Accepted February 1, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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