title: Two distinct ATP signaling mechanisms in differentiated neuroblastoma x glioma hybrid NG108-15 cells.
abstract: The ATP signaling mechanism in neuroblastoma x glioma hybrid NG108-15 cells differentiated by exposure to dibutyryl-cAMP was characterized. In cells loaded with fura-2, ATP rapidly raised the cytosolic Ca2+ concentration ([Ca2+]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 Mg2+. Inositol-1,4,5-trisphosphate (IP3) generation induced by ATP was totally blocked by removal of extracellular Ca2+, but residual IP3 generation still remained in nondifferentiated cells. In addition, ATP produced a concentration-, time-, and Mg(2+)-dependent biphasic uptake of 45Ca2+. 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 45Ca2+ uptake. 45Ca2+ 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 [Ca2+]i rise was transient and was insensitive to the extracellular Na+ concentration. Na+ influx, entry of ethidium bromide, and 45Ca2+ uptake were unaffected by bradykinin. Furthermore, bradykinin-evoked IP3 generation was insensitive to extracellular Ca2+. Neither ATP nor bradykinin had any effect on cAMP levels within cells. These data suggest that ATP induces a [Ca2+]i rise in differentiated NG108-15 cells via two distinct Ca2+ influx mechanisms, i.e., a receptor-operated cation channel and pores formed by ATP4-. These mechanisms are distinct from those elicited by bradykinin.
authors.affiliation: Department of Biochemistry, National Defense Medical Center, Taipei, Taiwan, R.O.C.
authors.forename: S H
authors.initials: SH
authors.lastname: Chueh
authors.forename: L S
authors.initials: LS
authors.lastname: Hsu
authors.forename: S L
authors.initials: SL
authors.lastname: Song
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D001920:Bradykinin / Q000494:pharmacology; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation; D005910:Glioma / Q000378:metabolism* / Q000473:pathology; D006822:Hybrid Cells; D007473:Ion Channels / Q000187:drug effects; D009447:Neuroblastoma / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction; D012964:Sodium / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D007473:Ion Channels; D003994:Bucladesine; D000255:Adenosine Triphosphate; D012964:Sodium; D001920:Bradykinin; D002118:Calcium