Extracellular ATP stimulates inositol phospholipid turnover and calcium influx in C6 glioma cells.
Extracellular ATP caused a dose-dependent accumulation of inositol phosphates and a rise in cytosolic free Ca2+ ([Ca2+]i) in C6 glioma cells with an EC50 of 60 +/- 4 and 10 +/- 5 microM, respectively. The threshold concentration of ATP (3 microM) for increasing [Ca2+]i was approximately 10-fold less than that for stimulating phosphoinositide (PI) turnover. The PI response showed a preference for ATP; ADP was about 3-fold less potent than ATP but had a comparable maximal stimulation (11-fold of the control). AMP and adenosine were without effect at concentrations up to 1 mM. ATP-stimulated PI metabolism was found to be partially dependent on extracellular Ca2+ and Na+ but was resistant to tetrodotoxin, saxitoxin, amiloride, ouabain, and inorganic blockers of Ca2+ channels (Co2+, Mn2+, La3+, or Cd2+). In Ca(2+)-free medium, ATP caused only a transient increase in [Ca2+]i as opposed to a sustained [Ca2+]i increase in normal medium. The ATP-induced elevation of [Ca2+]i was resistant to Na+ depletion and treatment with saxitoxin, verapamil and nisoldipine, but was attenuated by La3+. The differences in the characteristics of ATP-caused P1 hydrolysis and [Ca2+]i rise suggest that ATP receptors are independently coupled to phospholipase C and receptor-gated Ca2+ channels. Because of the robust effect of ATP in stimulating PI turnover and the apparent absence of P1-purinergic receptors, the C6 glioma cell line provides a useful model for investigating the transmembrane signalling pathway induced by extracellular ATP. The mechanisms underlying the unexpected finding of [Na+]o dependency for ATP-induced PI turnover require further investigation.
Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, R.O.C.
W W
WW
Lin
D M
DM
Chuang
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005910:Glioma / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D011983:Receptors, Purinergic / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects*; D012964:Sodium / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D010716:Phosphatidylinositols; D011983:Receptors, Purinergic; D000255:Adenosine Triphosphate; D012964:Sodium; D002118:Calcium