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The metabolic fate of glutamate in astrocytes has been controversial since several studies reported > 80% of glutamate was metabolized to glutamine; however, other studies have shown that half of the glutamate was metabolized via the tricarboxylic acid (TCA) cycle and half converted to glutamine. Studies were initiated to determine the metabolic fate of(More)
Since lactate released by glial cells may be a key substrate for energy in neurons, the kinetics for the uptake of L-[U-14C]lactate by cortical synaptic terminals from 7- to 8-week-old rat brain were determined. Lactate uptake was temperature-dependent, and increased by 64.9% at pH 6.2, and decreased by 43.4% at pH 8.2 relative to uptake at pH 7.3. Uptake(More)
There have been numerous studies on the activity and localization of aspartate aminotransferase (AAT) and glutamate dehydrogenase (GDH) in brain tissue. However, there is still a controversy as to the specific roles and relative importance of these enzymes in glutamate and glutamine metabolism in astrocytes and neurons or synaptic terminals. There are many(More)
Several reports indicate that lactate can serve as an energy substrate for the brain. The rate of oxidation of this substrate by cultured rat brain astrocytes was 3-fold higher than the rate with glucose, suggesting that lactate can serve as an energy source for these cells. Since transport into the astrocytes may play an important role in regulating(More)
Several recent studies have demonstrated that the metabolism of energy substrates takes place in multiple compartments in both astrocytes and synaptic terminals from brain. There are a number of differences in the metabolism of astrocytes and synaptic terminals primarily due to the localization of key enzymes such as pyruvate carboxylase and glutamine(More)
It is well documented that the brain preferentially utilizes alternative substrates for energy during brain development; however, less is known about the use of these substrates by synaptic terminals. The present study compared the rates of 14CO2 production from 1 mM D-[6-14C]glucose, L-[U-14C]glutamine, D-3-hydroxy[3-14C]butyrate, L-[U-14C]lactate and(More)
Studies from several groups have provided evidence that glutamate and glutamine are metabolized in different compartments in astrocytes. In the present study we measured the rates of 14CO2 production from U-[14C]glutamate and U-[14C]glutamine, and utilized both substrate competition experiments and the transaminase inhibitor aminooxyacetic acid (AOAA) to(More)
Most of the malic enzyme activity in the brain is found in the mitochondria. This isozyme may have a key role in the pyruvate recycling pathway which utilizes dicarboxylic acids and substrates such as glutamine to provide pyruvate to maintain TCA cycle activity when glucose and lactate are low. In the present study we determined the activity and kinetics of(More)
Malate has a number of key roles in the brain, including its function as a tricarboxylic acid (TCA) cycle intermediate, and as a participant in the malate-aspartate shuttle. In addition, malate is converted to pyruvate and CO2 via malic enzyme and may participate in metabolic trafficking between astrocytes and neurons. We have previously demonstrated that(More)
The rates of [6-14C]-glucose oxidation by reconstituted systems of cytosol and mitochondria or cytosol and synaptosomes were essentially the same as the rate of oxidation of [3-14C]-3-hydroxybutyrate. However, the rate of [U-14C]-glutamine oxidation by mitochondria was 2.5 times that by synaptosomes. The addition of glutamine (5 mM) caused a reduction in(More)