Long-term kainic acid exposure reveals compartmentation of glutamate and glutamine metabolism in cultured cerebellar neurons

Abstract

Glutamate neurotoxicity is implicated in most neurodegenerative diseases, and in the present study the long-term effects of the glutamate agonist kainic acid (KA) on cerebellar neurons are investigated. Primary cell cultures, mainly consisting of glutamatergic granule neurons, were cultured in medium containing 0.05 or 0.50mM KA for 7 days and subsequently incubated in medium containing [U-13C]glutamate or [U-13C]glutamine. The amount of protein and number of cells were greatly reduced in cultures exposed to 0.50 mM KA compared to those exposed to 0.05 mM KA. Glutamine consumption was not affected by KA concentration, whereas that of glutamate was decreased by high KA, confirming reduction in glutamate transport reported earlier. Neurons cultured with 0.50 mM KA and incubated with glutamate contained decreased amounts of glutamate, aspartate and GABA compared to those cultured with 0.05 mM KA. Incubation of cells exposed to 0.50 mM KA with glutamine led to an increased amount of glutamate compared to cells exposed to 0.05 mM KA, whereas the intracellular amounts of aspartate and GABA remained unaffected by KA concentration. Furthermore, mitochondrial metabolism of alpha-[U-13C]ketoglutarate derived from [U-13C]glutamate and [U-13C]glutamine was significantly reduced by 0.50 mM KA. The results presented illustrate differential vulnerability to KA and can only be understood in terms of inter- and intracellular compartmentation.