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Manganese decreases glutamate uptake in cultured astrocytes
1Laboratory of Neuropathology, Veterans Administration Medical Center, Miami, Florida 33125, USA.
Abstract:
Recent data have shown an accumulation of manganese in the basal ganglia in patients with chronic hepatic encephalopathy (HE). Astrocytes and ammonia are critically involved in the pathogenesis of HE, and we have recently demonstrated that ammonia decreases glutamate uptake in cultured astrocytes. Since failure by astrocytes to take up glutamate may represent an important pathogenetic mechanism in HE, we, therefore, examined the effect of manganese on glutamate transport in these cells. Treatment of cultured astrocytes with 100 microM manganese for 2 days resulted in a 54% decrease in the uptake of D-aspartate, a nonmetabolizable analogue of glutamate. Kinetic analysis revealed a 28% decline in Vmax, with no change in the K(m). Treatment of cultures with 5 mM NH4 Cl inhibited D-aspartate uptake by 21%, and a combination of 5 mM NH4Cl with 100 microM manganese produced an additive effect on uptake inhibition. These results suggest a pathogenetic role for manganese in HE, possibly involving glutamate transport.
Insights
Manganese accumulation in hepatic encephalopathy (HE) impairs astrocyte glutamate uptake. This study shows manganese directly reduces glutamate transport in astrocytes, suggesting a role in HE pathogenesis.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Chronic hepatic encephalopathy (HE) is associated with manganese accumulation in the basal ganglia.
- Astrocytes and ammonia play key roles in HE pathogenesis.
- Ammonia has been shown to decrease glutamate uptake in cultured astrocytes.
Purpose of the Study:
- To investigate the effect of manganese on glutamate transport in cultured astrocytes.
- To determine if manganese contributes to impaired astrocyte function in HE.
Main Methods:
- Primary astrocyte cultures were treated with manganese (100 microM) or ammonium chloride (5 mM).
- D-aspartate, a glutamate analogue, uptake was measured to assess glutamate transport.
- Kinetic analysis (Vmax, Km) was performed to characterize transport changes.
Main Results:
- Manganese treatment significantly decreased D-aspartate uptake by 54%.
- Kinetic analysis showed a 28% reduction in Vmax, indicating impaired transport capacity.
- Ammonium chloride alone inhibited uptake by 21%; combined manganese and ammonia showed additive inhibition.
Conclusions:
- Manganese directly impairs glutamate transport in astrocytes.
- This manganese-induced defect in glutamate uptake may be a contributing factor to the pathogenesis of hepatic encephalopathy.
- These findings highlight a potential therapeutic target for HE.