Two distinct ATP signaling mechanisms in differentiated neuroblastoma x glioma hybrid NG108-15 cells
Chueh, S.H.; Hsu, L.S.; Song, S.L.
Molecular Pharmacology 45(3): 532-539
1994
ISSN/ISBN: 0026-895X PMID: 7511780 Document Number: 429674
The ATP signaling mechanism in neuroblastoma times glioma hybrid NG108-15 cells differentiated by exposure to dibutyryl-cAMP was characterized. In cells loaded with fura-2, ATP rapidly raised the cytosolic Ca-2+ concentration ((Ca-2+)-i); the magnitude of the rise was inversely proportional to the extracellular Na+ concentration. Large increases in cytosolic Na+ concentration, measured with the fluorescent Na+ indicator sodium-binding benzofuran isophthalate, were dose-dependently elicited by ATP. ATP also evoked the entry of ethidium bromide into cells, and this process was inhibited by Mg-2+. Inositol-1,4,5-trisphosphate(IP-3) generation induced by ATP was totally blocked by removal of extracellular Ca-2+, but residual IP-3 generation still remained in nondifferentiated cells. In addition, ATP produced a concentration-, time-, and Mg-2+-dependent biphasic uptake of 45Ca-2+. A range of nucleotides and ATP analogues, including CTP, UTP, and GTP, induced only 9-29% of the ATP response. However, adenosine 5'-thiotriphosphate evoked 79% of ATP-induced 45Ca-2+ uptake. 45Ca-2+ uptake elicited by ATP could be potently blocked by purinoceptor antagonists, but other tested reagents less effectively blocked the action of ATP. When bradykinin was used as an agonist, the (Ca-2+)-i rise was transient and was used as an agonist, the (Ca-2+)-i rise was transient and was insensitive to the extracellular Na+ concentration. Na+ influx, entry of ethidium bromide, and 45Ca-2+ uptake were unaffected by bradykinin. Furthermore, bradykinin-evoked IP-3 generation was insensitive to extracellular Ca-2+. Neither ATP nor bradykinin had any effect on cAMP levels within cells. These data suggest that ATP induces a (Ca-2+)-i rise in differentiated NG108-15 cells via two distinct Ca-2+ influx mechanisms, i.e., a receptor-operated cation channel and pores formed by ATP-4-. These mechanisms are distinct from those elicited by bradykinin.