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 [Ca 2+ ] i was measured fluorimetrically with the Ca 2+ indicator dye, Fura‐2 3 Depolarization with K + caused a time‐ and dose‐dependent increase in [Ca 2+ ] j (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 [Ca 2+ ] i were inhibited dose‐dependently by the L‐type voltage‐sensitive Ca 2+ channel closer( R +)‐BayK8644, with IC 50 values of 53.4 nM and 87.9 nM respectively. 5 These data show a close temporal and dose‐response relationship between Ca 2+ entry via L‐type voltage‐sensitive Ca 2+ channels and Ins(1,4,5)P 3 formation following depolarization with K + , indicating that Ca 2+ influx can activate phospholipase C in SH‐SY5Y cells