Abstract
Murine neuronal and glial cell cultures exposed briefly to glutamate accumulated large amounts of 45Ca2+ from the extracellular medium during the exposure. Most of the accumulation likely reflected influx into neurons, as little accumulation was observed in similarly treated glial cultures. When the concentration of glutamate was varied between 10 and 1000 microM, or exposure duration was varied between 0 and 10 min, the amount of 45Ca2+ accumulation correlated closely with the amount of neuronal death 24 hr later. Both 45Ca2+ accumulation and cell death could be attenuated in a dose-dependent manner by the competitive NMDA antagonist D-aminophosphonovalerate or the noncompetitive antagonist dextrorphan, with IC50 values of approximately 100 microM and 15 microM, respectively. In contrast, neither 45Ca2+ accumulation nor cell death was blocked by the alpha-amino-3-hydroxy-5-methyl-4- isoxazole propionic acid (AMPA)/kainate antagonist 6-cyano-7- nitroquinoxaline-2,3-dione (CNQX) in the presence of high glycine. With brief exposure, high concentrations of AMPA, kainate, or K+ produced much less death or 45Ca2+ accumulation than produced by glutamate, especially if 10 microM MK-801 was included in the exposure medium to block NMDA receptor activation. Kainate- or AMPA-induced 45Ca2+ accumulation or neuronal cell death was blocked with CNQX. However, high K(+)-triggered 45Ca2+ accumulation was only partially blocked with CNQX plus MK-801, consistent with mediation by voltage-gated Ca2+ channels. In addition to measuring the accumulation of 45Ca2+ occurring during agonist exposure, we also assessed accumulation during the 30 min immediately following completion of a 3–5 min exposure to 500 microM NMDA.(ABSTRACT TRUNCATED AT 250 WORDS)
