抄録
Extracellular ATP interacts with membrane-bound receptors to induced several physiological functions. The signal transaction pathways associated with the various ATP receptor subtypes have not been fully elucidated. In the present study, we demonstrate the second messenger signaling responses mediated by different ATP receptor subtypes in NG108-15 cells. In fura 2-loaded cells, we observed two different Ca2+ signaling pathways in response to ATP; one was a intracellular Ca2+ mobilization mediated by phospholipase C activation, and the other was Ca2+ influx via nonselective cation channel. The former effect was induced by lower concentration of ATP (1-100μM) and functionally related with the initial transient increase in intracellularCa2+ level ([Ca2+]i), whereas the later effect required higher concentration of ATP above 500 μM and produced a sustained increase in [Ca2+]i. The effects of several ATP analogues on [Ca2+]i indicated that two distinct receptor subtypes, P2u and P2z, were involved in ATP-induced the Ca2+ mobilization and Ca2+ influx, respectively. The stimulation of NG108-15 cells with ATP also increased cyclic AMP level. This effect of ATP was mediated by a unique receptor population different from P2u or P2z subtypes, since UTP and BzATP had little effect on cyclic AMP level. Similar effects on cyclic AMP response were observed with βγMeATP, ATPγS, AppNHp, ADPβS and FSBA, but P2x agonist αβMeATP and P2y agonist 2MeSATP were without effect, indicating that ATP induced cyclic AMP accumulation was mediated by a novel purinergic receptor subtype. These results indicate that NG108-15 cells possess at least three different ATP receptors which are coupled to different signal transduction mechanisms.
