Identification of P2-purinergic receptors

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1) PC12 pheochromocytoma cells have P2 receptors which are coupled to Ca2+influx and catecholamine release. In the presence of forskolin, an activator of adenylyl cyclase, ATP analogs such as ATP and 2-methylthio ATP inhibited cyclic AMP accumulation in a concentration-dependent manner. Treatment with pertussis toxin, which completely abolished the effect of carbachol, had no effect on the action of ATP.In addition, we found that ADP-ribosylation factors translocate to membranes from the cytosol fraction after exocytotic stimulation. The cloning of a new type of ATP receptor remains to be determined.2) Nitric oxide (NO) modulates the release of neurotransmitters. Previously we reported that 5-nitroso-cysteine stimulated noradrenaline release from hippocampus in vivo and in vitro. In PC12 cells, S-nitroso-cysteine did inhibit noradrenaline release. Other NO compounds, which increased cyclic GMP accumulation, had no effect. ATP-stimulated Ca2+ influx via Ca2+ channels was inhibited in PC12 cells treated with S-Nitroso-cysteine, although S-nitroso-cysteine stimulated Ca2+ mobilization from intracellular caffeine-sensitive Ca2+-pools. Ca2+ mobilization by NO from Ca2+ pools was not a sufficient factor, and other factors stimulating release may be regulated negatively.3) Lipopolysaccaride or cytokines are known to stimulate production of nitrite via expression of inducible NO synthase (iNOS) in rat glial cells. Co-addition of endothelin decreased iNOS expression and nitrite accumulation by stimulants. In contrast, pretreatment with endothelin or ATP for 24 h enhanced iNOS expression. The stimulatory effect by endothelin or ATP was mediated by ET-B or P2 receptors, respectively. A protein kinase C inhibitor suppressed endothelin- and ATP-enhanced iNOS expression. Stimulation of ATP receptors induced activation of a nuclear factor, NFkB in glial cells.