ATP-evoked inositol phosphates formation through activation of P2U purinergic receptors in cultured astrocytes: Regulation by PKC subtypes α, δ, and θ
✍ Scribed by Ching C. Chen; Wei C. Chen
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 974 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0894-1491
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✦ Synopsis
ATP-induced phosphoinositide (PI) hydrolysis was studied in cultured astrocytes. To characterize the Pz purinergic receptor-mediated effects of ATP, the subtype-specific agonists 2-methylthio ATP (2-MeSATP1, UTP, and a,P-methylene ATP were compared. ATP, UTP, or 2-MeSATP induced a dose-dependent increase of inositol phosphates (IP) accumulation; a,P-methylene ATP and adenosine had no effect. The order of potency was ATP -S UTP >> 2-MeSATP. Cross-desensitization experiments indicated that ATP interacted with both Pzu and Pzy receptors. Pzu was the predominant Pz receptor in mediating PI hydrolysis in astrocytes. The effect of ATP, UTP, or 2-MeSATP was markedly inhibited by pretreatment of cells with pertussis toxin (PTX), indicating that both Pzu and Pzy receptors coupled to phospholipase C through PTX-sensitive G protein. Short-term (10 min) treatment of cells with 1 pM TPA attenuated ATP, UTP, and 2-MeSATP-induced PI breakdown; however, long-term (24 h) pretreatment resulted in marked potentiation of both ATP and UTP, and restoration of 2-MeSATP responses. In a further analysis of the effect of TPA, 10 min and 1.5 h pretreatment attenuated ATPand UTP-induced PI breakdown, but this inhibitory action was lost after 3 h of treatment. Both 6 and 24 h pretreatments resulted in a potentiation. Western blot analysis showed translocation of protein kinase C (PKC)cx, -6, and -8 from the cytosol to the membrane following 10 min and 1.5 h treatments, and restoration to basal levels in the membrane fraction was seen after 3 h of treatment. On the other hand, partial and complete downregulation of these three isoforms was seen after 6 and 24 h of treatment, respectively. PKCq was translocated but not down-regulated by TPA. These results suggested that PKCcx, -6, and -8, but not -q may exert tonic inhibition on Pzu receptor-mediated PI turnover in unstimulated astrocytes.