Suppression of programmed neuronal death by a thapsigargin-induced Ca2+ influx

Rat sympathetic neurons undergo programmed cell death (PCD) in vitro and in vivo when they are deprived of nerve growth factor (NGF). Chronic depolarization of these neurons in cell culture with elevated concentrations of extracellular potassium (K⁺]_o) prevents this death. The effect of prolonged depolarization on neuronal survival is thought to be mediated by a rise of intracellular calcium concentration (Ca²⁺]_i) caused by Ca²⁺ influx through voltage-gated channels. In this report we investigate the effects of chronic treatment of rat sympathetic neurons with thapsigargin, an inhibitor of intracellular Ca²⁺ sequestration. In medium containing a normal concentration of extracellular Ca²⁺ (Ca²⁺]_o), thapsigargin caused a sustained rise of intracellular Ca²⁺ concentration and partially blocked death of NGF-deprived cells. Elevating Ca²⁺]_o in the presence of thapsigargin further increased Ca²⁺]_i, suggesting that the sustained rise of Ca²⁺]_i was caused by a thapsigargin-induced Ca²⁺ influx. This treatment potentiated the effect of thapsigargin on survival. The dihydropyridine Ca²⁺ channel antagonist, nifedipine, blocked both a sustained elevation of Ca²⁺]_i and enhanced survival caused by depolarization with elevated K⁺]_o, suggesting that these effects are mediated by Ca²⁺ influx through L-type channels. Nifedipine did not block the sustained rise of Ca²⁺]_i or enhanced survival caused by thapsigargin treatment, indicating that these effects were not mediated by influx of Ca²⁺ through L-type channels. These results provide additional evidence that increased Ca²⁺]_i can suppress neuronal PCD and identify a novel method for chronically raising neuronal Ca²⁺]_i for investigation of this and other Ca²⁺-dependent phenomena. © 1995 John Wiley & Sons, Inc.