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Desensitization of “metabotropic” glutamate receptors: Involvement of protein kinase C
Pharmacological Research, Vol. 22, S upplement 2, 1990
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DESENSITIZATION OF "METABOTROPIC" GLUTAMATE RECEPTORS: INVOLVEMENT OF PROTEIN KINASE C. M.V. Catania, M.A. sortino, F. Nicoletti, and P.L. Canonico. Institute of pharmacology, University of Catania, Italy. Continuous exposure of cultured neurons to excitatory amino acids led to a rapid and long-lasting desensitization of glutamate receptors coupled to polyphosphoinositide (PPI) hydrolysis. Desensitization developed through the succession of at least two independent stages, characterized by a differential sensitivity to protein kinase C inhibitors. Accordingly, the reduction of receptor responsiveness resulting from short exposure to glutamate (30 min) was markedly attenuated by polymyxin B sulfate (30 ~g/ml), sphingosine sulfate (10 ~M). as well as by the glycosphingolipids. GMl (100 ~M) and GTlb (10 ~M). Inhibitors of calpain (leupeptin. 100 ~M) or arachidonic acid metabolism (indomethacin, 10 ~M or nordihydroguaiaretic acid, 10 ~M) were inactive. None of the protein kinase C inhibitors attenuated receptor desensitizazion after 6-hour exposure to glutamate. The involvement of protein kinase C in the short -term component of receptor desensitizat ion is supported by the evidence that addition of phorbol esters or synthetic diacylglycerols to cultured neurons inhibited the stimulation of inositol phospholipid hydrolysis induced by glutamate and quisqualate. The lack of changes in the number or affinity of (3H]glutamate binding after 30-min exposure to glutamate suggests that phosphorylation of the recognition site by protein kinase C is not responsible for desensitization of metabotropic receptors. We speculate that protein kinase C acts to reduce the efficiency of the coupling mechanism between recogn it ion sites and phospholipase C. Whether this mechanism involves the phosphorylation of a specific STP-binding protein remains to be established.
1043-661 8/90/22110103-{)I/ S03.00/0
© 1990 The Italian Ph armacological Society
!O3
DESENSITIZATION OF "METABOTROPIC" GLUTAMATE RECEPTORS: INVOLVEMENT OF PROTEIN KINASE C. M.V. Catania, M.A. sortino, F. Nicoletti, and P.L. Canonico. Institute of pharmacology, University of Catania, Italy. Continuous exposure of cultured neurons to excitatory amino acids led to a rapid and long-lasting desensitization of glutamate receptors coupled to polyphosphoinositide (PPI) hydrolysis. Desensitization developed through the succession of at least two independent stages, characterized by a differential sensitivity to protein kinase C inhibitors. Accordingly, the reduction of receptor responsiveness resulting from short exposure to glutamate (30 min) was markedly attenuated by polymyxin B sulfate (30 ~g/ml), sphingosine sulfate (10 ~M). as well as by the glycosphingolipids. GMl (100 ~M) and GTlb (10 ~M). Inhibitors of calpain (leupeptin. 100 ~M) or arachidonic acid metabolism (indomethacin, 10 ~M or nordihydroguaiaretic acid, 10 ~M) were inactive. None of the protein kinase C inhibitors attenuated receptor desensitizazion after 6-hour exposure to glutamate. The involvement of protein kinase C in the short -term component of receptor desensitizat ion is supported by the evidence that addition of phorbol esters or synthetic diacylglycerols to cultured neurons inhibited the stimulation of inositol phospholipid hydrolysis induced by glutamate and quisqualate. The lack of changes in the number or affinity of (3H]glutamate binding after 30-min exposure to glutamate suggests that phosphorylation of the recognition site by protein kinase C is not responsible for desensitization of metabotropic receptors. We speculate that protein kinase C acts to reduce the efficiency of the coupling mechanism between recogn it ion sites and phospholipase C. Whether this mechanism involves the phosphorylation of a specific STP-binding protein remains to be established.
1043-661 8/90/22110103-{)I/ S03.00/0
© 1990 The Italian Ph armacological Society