Ionotrophic 5-hydroxytryptamine type 3 receptor activates the protein kinase C-dependent phospholipase D pathway in human T-cells

The present study was undertaken to investigate the role of the 5-hydroxytr yptamine (5-HT) ionotrophic receptor 5-HT3 in the activation of human Jurka t T-cells. 5-HT and 2-methyl-5-HT (2Me-5-HT), an agonist of the 5-HT3 recep tor, induced increases in intracellular free Na+ concentrations, [Na+](i), via opening of the ionotrophic receptor in these cells. These two serotoner gic (5-hydroxytryptaminergic) agents potentiated phytohaemagglutinin (PHA)- induced T-cell activation. However, they failed to potentiate dioctanoglyce rol-plus-ionomycin-stimulated T-cell blastogenesis. Interestingly, an inhib itor of protein kinase C (PKC), GF 109203X, curtailed significantly 5-HT an d 2Me-5-HT-potentiated T-cell activation. These results demonstrate that th e opening of the 5-HT3 ionotrophic receptor is implicated in T-cell activat ion via the PKC pathway. Furthermore, 5-HT and 2Me-5-HT stimulated phosphol ipase D (PLD) activity, as measured by the production of phosphatidylethano l and phosphatidylbutanol at the expense of phosphatidic acid (PA). GF 1092 03X significantly curtailed the 5-HT- and 2Me-5-HT-induced PLD activity and T-cell activation. The PLD/PA. pathway stimulated by these two serotonergi c agents resulted in the production of 1,2-diacylglycerol (DAG) mass in Jur kat T-cells. These results altogether suggest that 5-HT and 2Me-5-HT potent iate T-cell activation via increases in [Na+](i) and the activation of the PKC-dependent PLD pathway.