SUPPRESSION OF PROGRAMMED NEURONAL DEATH BY A THAPSIGARGIN-INDUCED CA2+ INFLUX

Rat sympathetic neurons undergo programmed cell death (PCD) in vitro a nd in vivo when they are deprived of nerve growth factor (NGF). Chroni c depolarization of these neurons in cell culture with elevated concen trations of extracellular potassium ([K+](0)) 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 repo rt we investigate the effects of chronic treatment of rat sympathetic neurons with thapsigargin, an inhibitor of intracellular Ca2+ sequestr ation. In medium containing a normal concentration of extracellular Ca 2+ ([Ca2+](0)), 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 a ntagonist, nifedipine, blocked both a sustained elevation of [Ca2+](i) and enhanced survival caused by depolarization with elevated [K+](0), suggesting that these effects are mediated by Ca2+ influx through L-t ype channels. Nifedipine did not block the sustained rise of [Ca2+](i) or enhanced survival caused by thapsigargin treatment, indicating tha t these effects were not mediated by influx of Ca2+ through L-type cha nnels. These results provide additional evidence that increased [Ca2+] (i) can suppress neuronal PCD and identify a novel method for chronica lly raising neuronal [Ca2+](i) for investigation of this and other Ca2 +-dependent phenomena. (C) 1995 John Wiley and Sons, Inc.