title: Receptor-induced heterologous desensitization of receptor-regulated phospholipase C.
abstract: Activation of the P2Y purinoceptor on turkey erythrocytes results in a G11-mediated activation of a phospholipase C-beta isoenzyme and hydrolysis of polyphosphoinositides. The role of the protein kinase C and Ca(2+)-mobilizing arms of the inositol lipid signalling cascade in P2Y purinoceptor-induced desensitization of phospholipase C has been examined using erythrocytes as a model system. Preincubation of intact erythrocytes with either P2Y purinoceptor agonist, ADP beta S, or the protein kinase C-activating phorbol ester, phorbol 12-myristate, 13 acetate (PMA), resulted in a time of preincubation-dependent decrease in guanine nucleotide-, P2Y purinoceptor-, and beta-adrenoceptor-stimulated phospholipase C activities in membranes isolated from these cells. The extent of heterologous desensitization induced by ADP beta S and PMA were additive suggesting that they did not share a common mechanism. A lack of involvement of activation of protein kinase C in P2Y purinoceptor-induced heterologous desensitization was further supported by the observation that although protein kinase C inhibitors or down-regulation of protein kinase C resulted in a loss of PMA-induced desensitization, neither treatment affected the extent of P2Y purinoceptor-induced desensitization. In addition, elevation of intracellular Ca2+ or prevention of its elevation did not induce heterologous desensitization and had no effect on the desensitization induced by ADP beta S. Thus, neither the protein kinase C nor Ca2+ mobilizing arms of the inositol lipid signalling pathway appear to be involved in P2Y purinoceptor promoted heterologous desensitization of phospholipase C. These results are consistent with the existence of a novel feedback pathway for agonist-induced heterologous desensitization of a second messenger generating enzyme. Preincubation of cells with ADP beta S or the beta-adrenoceptor agonist, isoproterenol, followed by rechallenge with each of the receptor agonists revealed that receptor-specific desensitization occurs in addition to heterologous desensitization. Thus, multiple mechanisms account for agonist-induced desensitization of the inositol lipid signalling system of turkey erythrocytes.
authors.affiliation: Department of Pharmacology, University of North Carolina at Chapel Hill, School of Medicine 27599-736, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Galas
authors.forename: T K
authors.initials: TK
authors.lastname: Harden
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004912:Erythrocytes / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D011983:Receptors, Purinergic / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D013997:Time Factors; D014422:Turkeys; D010738:Type C Phospholipases / Q000378:metabolism* / Q000502:physiology
chemical_list: D011983:Receptors, Purinergic; D006160:Guanosine Triphosphate; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D007545:Isoproterenol