Sustained Ca2+-induced Ca2+-release underlies the post-glutamate lethal Ca2+ plateau in older cultured hippocampal neurons

Several studies have shown that a prolonged Ca2+ elevation follows a glutamate-mediated excitotoxic insult in cultured neurons, and may be associated with impending cell death. Recently, we showed that the prolonged Ca2+ elevation that emerges as neurons age in culture is specifically linked to an age-related increase in excitotoxic vulnerability. However, the multiple sources of Ca2+ that contribute to Ca2+ elevation during and after glutamate exposure are not well understood. Here, we examined the Ca2+ sources of the age-related prolonged Ca2+ elevation in cultured hippocampal neurons. Studies with caffeine showed that the ryanodine receptor-dependent releasable pool of Ca2+ from intracellular stores was similar in older and younger neurons. Thapsigargin, which inhibits intracellular store refilling, did not mimic the age-related prolonged Ca2+ elevation and, in fact, partially reduced it. Ryanodine, which blocks Ca2+-induced Ca2+ -release (CICR) from stores, completely blocked the age-related prolonged Ca2+ elevation following glutamate exposure but did not alter maximal Ca2+ elevation during the glutamate exposure. Thus, we conclude that sustained CICR plays a selective and key role in generating the lethal, age-related, prolonged Ca2+ elevation, and is the likely mechanism underlying age-related, enhanced vulnerability to excitotoxicity in neurons. (C) 2002 Elsevier Science B.V. All rights reserved.