Endothelin-1 increases arachidonic acid release in C6 glioma cells through a potassium-modulated influx of calcium.
Endothelin-1 (Et-1) but not a range of other receptor agonists stimulated the release of arachidonic acid (AA) in C6 glioma. Et-1 activation was concentration dependent and was inhibited by chelation of extracellular calcium. The calcium ionophores A23187 and ionomycin could also stimulate release of AA. Et-1 caused an early increase in intracellular Ca2+ concentration ([Ca2+]i) followed by a sustained but lower plateau level. The sensitivity of the response to quinacrine, its dependence on Ca2+, and the demonstration of an increase in phospholipase A2 (PLA2) activity that was insensitive to dithiothreitol suggested that the release of AA was due to activation of cytosolic PLA2 in the cells. Staurosporine, a protein kinase C (PKC) inhibitor, had no effect on Et-1-induced AA release but abolished that by phorbol 12-myristate 13-acetate, demonstrating that the Et-1 response was PKC independent. Raised levels of extracellular KCl inhibited both AA release and the increase in [Ca2+]i triggered by Et-1, whereas valinomycin, which causes K+ efflux, not only caused a rapid rise in [Ca2+]i but also caused AA mobilisation. The results therefore suggest that Et-1 activation of PLA2 in this cell type requires calcium influx dependent on K+ efflux.
Dunican
D J
DJ
Department of Biochemistry, Trinity College, Dublin, Ireland.
Griffiths
R
R
Williams
D C
DC
O'Neill
L A
LA
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D016232:Endothelins / Q000494:pharmacology*; D004789:Enzyme Activation; D005910:Glioma / Q000378:metabolism*; D015640:Ion Channel Gating; D007476:Ionophores / Q000494:pharmacology; D010741:Phospholipases A / Q000502:physiology; D054467:Phospholipases A2; D011188:Potassium / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014634:Valinomycin / Q000494:pharmacology
D016232:Endothelins; D007476:Ionophores; D014634:Valinomycin; D016718:Arachidonic Acid; D000001:Calcimycin; D010741:Phospholipases A; D054467:Phospholipases A2; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium