Veratridine delays apoptotic neuronal death induced by NGF deprivation through a Na(+)-dependent mechanism in cultured rat sympathetic neurons.
Superior-cervical ganglion (SCG) cells dissociated from newborn rats depend on nerve growth factor (NGF) for survival. Membrane depolarization with elevated K+ is known to prevent neuronal death following NGF deprivation and/or to promote survival via a Ca(2+)-dependent mechanism. Here we have exploited the possibility of whether or not a Na(+)-dependent pathway for neuronal survival is present in these cells. Veratridine (EC50 = 40 nM), a voltage-dependent Na+ channel activator, significantly delayed the onset of apoptotic cell death in NGF-deprived SCG neurons that had been cultured for 7 days in the presence of NGF. This effect was blocked completely by Na+ channel blockers including tetrodotoxin (TTX, 1 microM), benzamil (25 microM) and flunarizine (1 microM), but was not attenuated by nimodipine (1 microM), an L-type Ca2+ channel blocker. The saving effect of veratridine on cultured neurons was observed even in low Ca2+ media (0-1.0 mM), but was completely abolished in a low Na+ medium (38 mM). Sodium-binding benzofuran is isophthalate was employed as a fluorescent probe for monitoring the level of cytoplasmic free Na+, which revealed a sustained increase in its level (12.9 mM, 307% of that of control) in response to veratridine (0.75 microM). The TTX or flunarizine completely blocked veratridine-induced Na+ influx in these cultured neurons. Moreover, no appreciable increase in intracellular Ca2+ was detected under these conditions. Though Na+ channels were effectual in SCG neurons which were freshly isolated from newborn rats, the Na(2+)-dependent saving effect of veratridine was not observed in these young neurons. These lines of evidence suggest that the death-suppressing effect of veratridine on cultured SCG neurons depends on the Na+ influx via voltage-dependent Na+ channels, and suggest the presence of Na(+)-dependent regulatory mechanism(s) in neuronal survival.
Tanaka
S
S
Molecular Neurobiology Laboratory, Hokkaido University, Faculty of Science, Sapporo, Japan.
Koike
T
T
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D066298:In Vitro Techniques; D009414:Nerve Growth Factors / Q000172:deficiency*; D009474:Neurons / Q000187:drug effects* / Q000473:pathology; D051381:Rats; D017208:Rats, Wistar; D015222:Sodium Channels / Q000187:drug effects*; D017783:Superior Cervical Ganglion / Q000187:drug effects* / Q000473:pathology; D014701:Veratridine / Q000494:pharmacology*
D009414:Nerve Growth Factors; D015222:Sodium Channels; D014701:Veratridine