Studies on the role of calcium in the 5-HT-stimulated release of glutamate from C6 glioma cells

We recently reported that 5-hydroxytryptamine(2A) (5-HT2A) receptor activation on cultured glial cells induces glutamate release [J. Neurosci. Res. 67 (2002) 399]. Here we use C6 glioma cells to examine the role of calcium in this response. 5-Hydroxytryptamine (5-HT) increases glutamate release from C6 glioma cells, an effect blocked by low calcium conditions. The calcium ionophores ionomycin and calcimycin also released glutamate from C6 glioma cells in a Ca2+-dependent manner, The effect of 5-HT was reduced by the phospholipase C inhibitor U73122 (1-[6[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione), but not its inactive enantomer U73343 (1-[6 [[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-2,5-pyrrolidinedione). The protein kinase C inhibitors staurosporine and calphostin C had no effect on the response to 5-HT, whereas the response was blocked by thapsigargin and caffeine. Neither the L-type calcium channel blockers, nifedipine and verapamil, nor the N-type calcium channel blocker omega-conotoxin GVlA inhibited the effect of 5-HT, whereas NiCl2 and KCl blocked the response to 5-HT. We conclude that the 5-HT-induced efflux of glutamate from C6 glioma cells is Ca2+ dependent and involves, at least in part, the mobilisation of Ca2+ from mositol (1,4,5) tris phosphate (IP3) sensitive intracellular stores. (C) 2002 Elsevier Science B.V. All rights reserved.