ACTIVATION OF PHOSPHOLIPASE-C IN SH-SY5Y NEUROBLASTOMA-CELLS BY POTASSIUM-INDUCED CALCIUM-ENTRY

1 We used SH-SY5Y human neuroblastoma cells to investigate whether depolarization with high K+ could stimulate inositol (1,4,5)trisphosphate (Ins(1,4,5)P-3) formation and, if so, the mechanism involved. 2 Ins(1,4,5)P-3 was measured by a specific radioreceptor mass assay, whilst [Ca2+](i) was measured fluorimetrically with the Ca2+ indicator dye, Fura-2. 3 Depolarization with K+ caused a time- and dose-dependent increase in [Ca2+](i) (peak at 27 s, EC(50) of 50.0 +/- 9.0 mM) and Ins(1,4,5)P-3 formation (peak at 30 s, EC(50) of 47.4 +/- 1.1 mM). 4 Both the K+-induced Ins(1,4,5)P-3 formation and increase in [Ca2+](i) were inhibited dose-dependently by the L-type voltage-sensitive Ca2+ channel closer, (R+)-BayK8644, with IC50 values of 53.4 nM and 87.9 nM respectively. 5 These data show a close temporal and dose-response relationship between Ca2+ entry via L-type voltage-sensitive Ca2+ channels and Ins(1,4,5)P-3 formation following depolarization with K+, indicating that Ca2+ influx can activate phospholipase C in SH-SY5Y cells.