Low-level manganese exposure alters glutamate metabolism in GABAergic AF5 cells

Abstract

Recent studies have suggested that the globus pallidus may be a particularly sensitive target of manganese (Mn), however, in vitro studies of the effects of Mn on GABAergic neurons have been restricted by the lack of a cell model expressing GABAergic properties. Here we investigated the effects of low-level Mn treatment on cellular GABA and glutamate metabolism using the newly characterized AF5 rat neural-derived cell line, which displays GABAergic properties during culture in vitro. Intracellular GABA and glutamate levels were measured along with measurement of the release of GABA and glutamate into the culture medium, glutamine uptake from the culture medium, and the specific effects of Mn on the enzymes directly responsible for the synthesis and degradation of GABA, glutamate decarboxylase (GAD) and GABA transaminase (GABA-T). Our results demonstrate that Mn had no effect on the activities of GAD or GABA-T. Similarly, low-level Mn treatment of AF5 cultures had only a small effect on intracellular GABA levels (114% of control) and no effect on the release of GABA. In contrast, intracellular and extracellular glutamate levels were enhanced to 170% and 198% of control during Mn treatment, respectively, while extracellular glutamine decreased to 73% of controls. Together, these results suggest that glutamate homeostasis may be preferentially affected over GABA in AF5 cells during low-level Mn treatment, suggesting a novel mechanism by which Mn-induced excitotoxicity might arise.

A Chronic Iron-Deficient/High-Manganese Diet in Rodents Results in Increased Brain Oxidative Stress and Behavioral Deficits in the Morris Water Maze

“…It is possible that the changes we observed were due to alterations in glutamate metabolism or transport, since glutamate plays an indispensable role in learning and memory (RichterLevin et al 1995;Riedel and Reymann 1996). Additionally, other data suggest abnormal brain Mn accumulation affects various aspects of glutamatergic systems (Fitsanakis et al 2006;Crooks et al 2007;Erikson et al 2007). Interestingly, chronic liver failure, which can lead to increased brain Mn accumulation, has recently been shown to impair glutamate transmission in vivo (Monfort et al 2007).…”

Manganese accumulates primarily in nuclei of cultured brain cells

“…The half confluent cultures of Z310, RBE4, N27, or PC12 cells were exposed to 100 µM MnCl 2 containing 2.633 nCi 54 Mn/mL for 24 hrs. The exposure concentration was chosen because previous works by this and other laboratories have shown significant toxic outcomes in various cell types (Chen et al, 2001;Crooks et al, 2007;Li et al, 2005;Zheng and Zhao, 2001). Mn treatment was terminated by rapid aspiration of the medium, followed by thorough washes with 5 mL of ice cold PBS for three times.…”

Manganese and Huntington Disease

“…96,97 Manganese can also increase synaptic glutamate release and inhibit NMDA receptor conductance as a channel blocker. 98,99 HD models have shown reductions in protein and mRNA of another astrocytic glutamate transporter, GLT1, as well as reductions in astrocytic glutamate uptake. 94,100 As already discussed, the manganese-dependent enzyme arginase can also play a role in glutamate release by regulating production of ornithine, a precursor of glutamate.…”