Calcium influx via L-type voltage-gated channels mediates the delayed, elevated increases in steady-state c-fos mRNA levels in cerebellar granule cells exposed to excitotoxic levels of glutamate
✍ Scribed by Roger Griffiths; Lyndsay Ritchie; Kate Lidwell; Angus Grieve; Craig S. Malcolm; Mary Scott; Clive Meredith
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 442 KB
- Volume
- 52
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
The altered kinetics of steady-state c-fos mRNA production in cultured cerebellar granule cells under excitotoxic conditions was investigated in neurons subjected to depolarising stimuli, namely, high KCl and L-glutamate (Glu), in which Ca 2؉ influx occurs by differing routes. Increases in intracellular-free calcium levels ([Ca 2؉ ] i ) stimulated by nontoxic or toxic levels of Glu were blocked by selective N-methyl-Daspartate (NMDA) receptor antagonism; were blocked only partially by the L-type channel blocker, nifedipine; and were unaffected by ␣-amino-3-hydroxy-5methyl-4-isoxazole propionate (AMPA)/kainate receptor antagonists. Glu-induced cell death was prevented only by NMDA receptor blockade. Exposure of cells to nontoxic levels of Glu resulted in a transient increase in c-fos mRNA levels, whereas an excitotoxic dose produced a delay in the appearance of c-fos mRNA but a subsequent, progressive, and sustained (G4 hr) increase. An excitotoxic dose of Glu in combination with either nifedipine or selective NMDA receptor antagonists resulted in the normal, transient increase of c-fos mRNA levels. Chronic exposure to 55 mM KCl caused no cytotoxicity, although it resulted in a delayed, elevated increase in c-fos mRNA levels that was unaffected by NMDA receptor blockade but reverted to the normal, transient profile of c-fos mRNA formation when it was coadministered with nifedipine. The KCl-induced increase in [Ca 2؉ ] i levels was inhibited dramatically by nifedipine but was unaffected by any of the ionotropic Glu receptor antagonists. The results support the notion that the appearance of a delayed but elevated increase in steady-state c-fos mRNA levels following exposure to excitotoxic doses of Glu is mediated specifically by calcium influx via L-type voltage-gated channels. J.