Characterization of Na+ influx mediated by ATP(4-)-activated P-2 purinoceptors in PC12

1 Micromolar levels of extracellular ATP increased cytosolic Na+ concentration ([Na+](i)) as well as cytosolic Ca2+ concentration ([Ca2+](i)) in PC12 cells. 2 Pretreatment of cells with tetrodotoxin, benzamil or thapsigargin did not alter the ATP-induced Na+ influx. 3 Increased extracellular Mg2+ concentration decreased the ATP effect. Furthermore, when the extracellular ATP pool was treated to contain corresponding calculated concentrations of ATP(4-), the increase in [Na+](i) stayed linked to the ATP(4-) concentration rather than to the total ATP concentrations in the stimulants. 4 Extracellular ATP does not create nonselective pores as shown by the fact that ethidium bromide does not enter the cells upon ATP stimulation. 5 Among the tested nucleotides, only adenosine 5'-O-(3-thiotriphosphate), 2-methylthio ATP and 2-chloro ATP also caused Na+ influx. 6 Reactive Blue 2 specifically decreased the ATP effect in a concentration-dependent manner. 7 The results suggest that extracellular ATP triggers Na+ influx through a P-2 purinoceptor which is activated by ATP(4-) in PC12 cells.