BLOCK OF NEURONAL APOPTOSIS BY A SUSTAINED INCREASE OF STEADY-STATE FREE CA2+ CONCENTRATION

Programmed death is a ubiquitous feature of the development of the ver tebrate nervous system. This death is prevented in vivo by trophic fac tors and by afferent input. Death of neurons can also be prevented in culture models of programmed death by trophic factors and by chronic d epolarization with elevated concentrations of K+ in the culture medium . The latter effect is mediated by Ca2+ influx through voltage-gated c hannels and may prevent death by mimicking survival-promoting effects of naturally occurring electrical activity. Little is currently known about the mechanism by which either trophic factors or increased cytop lasmic Ca2+ promote survival.