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Effects of morphine on calcium regulated phosphorylation of synaptosomal cytosolic proteins from rat striatum


Journal of Pharmacology & Experimental Therapeutics 220(3): 696-702
Effects of morphine on calcium regulated phosphorylation of synaptosomal cytosolic proteins from rat striatum
A synaptosomal cytosolic fraction was prepared from rat striatum by differential centrifugation and lysis under hypotonic conditions. The endogenous phosphorylation of the synaptosomal cytosolic proteins was assayed in vitro using [.gamma.-32P]ATP as a phosphate donor. After resolution of the cytosolic proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis, specific protein phosphorylation was detected by autoradiography and quantified by microdensitometry. The addition of CaCl2 to the assay stimulated the phosphorylation of cytosolic proteins through a process that required the heat-stable Ca-binding protein, calmodulin. The acute administration of morphine resulted in a dose- and time-dependent increase in Ca-regulated phosphorylation of several proteins. This stimulation of phosphorylation by morphine was most apparent for proteins with MW of 50,000, 55,000 and 60,000 and reached levels as great as 200% above control. The prior administration of naloxone blocked the effects of morphine on phosphorylation. Rats rendered tolerant to the effects of morphine were tolerant to the morphine-induced stimulation of Ca-regulated phosphorylation. The effects of morphine on phosphorylation were shared by the morphine congeners, levorphanol and l-methadone, but not by their weaker stereoisomers, dextrorphan and d-methadone. The in vitro administration of morphine, its congeners and other opiate-like peptides did not affect protein phosphorylation. Some of the effects of opiates may be mediated through a protein phosphorylation process that is dependent on Ca and calmodulin.

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Accession: 005314995



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