Showing papers by "Jan O. Aasly published in 1998"
TL;DR: In cultured cortical astrocytes, pyruvate formed from [U-13C]glutamate was shown to re-enter the TCA cycle after conversion to acetyl-CoA, as demonstrated by the labelling patterns in aspartate C-2 and C-3, lactate C -2, and glutamate C-4, which provides evidence for pyruVate recycling in astroCytes.
Abstract: Pyruvate recycling is a well established pathway in the liver, but in the brain, the cellular localization of pyruvate recycling remains controversial and its physiological significance is unknown. In
64 citations
TL;DR: The present results indicate that glutamate‐to‐aspartate conversion is preferentially utilized by astrocytes when oxygen is available but glycolysis is impaired.
Abstract: The ability of cultured astrocytes to metabolize [U-13C]glutamate in the absence of glucose was investigated by utilizing 13C nuclear magnetic resonance spectroscopy to identify 13C-labeled metabolites. Control cultures (3 mM glucose), hypoglycemic cultures (glucose-deprived), severe hypoglycemic cultures (glucose-deprived, 0.5 mM iodoacetate as an inhibitor of glycolysis), hypoglycemic/hypoxic cultures, and cultures deprived of all additional substrates were incubated for 2 hr in medium containing 0.5 mM glutamate (50% [U-13C]glutamate). Glucose deprivation alone had little effect on removal of glutamate from the culture medium, but the presence of iodoacetate or incubating cultures in a low-oxygen atmosphere decreased glutamate clearance. Only the withdrawal of all substrates other than glutamate decreased glutamine synthesis. Metabolism of glutamate through the tricarboxylic acid (TCA) cycle was evident by the appearance of [1,2,3-13C]glutamate and [U-13C]aspartate in cell extracts and [U-13C]lactate in cell media. Lactate derived from TCA cycle intermediates was significantly reduced after glucose deprivation and even more so after severe hypoglycemia. Release of glutamate from astrocytes was observed under all incubation conditions. [U-13C]Aspartate was not detected in control media but was released from glucose-deprived cells when oxygen was available. Increased release was observed in the presence of iodoacetate. After withdrawal of all substrates other than glutamate, [U-13C]aspartate was the only metabolite observed intracellularly, whereas aspartate, glutamine, and 5-oxoproline were detected in the incubation medium. The present results indicate that glutamate-to-aspartate conversion is preferentially utilized by astrocytes when oxygen is available but glycolysis is impaired. J. Neurosci. Res. 51:636–645, 1998. © 1998 Wiley-Liss, Inc.
58 citations
TL;DR: Most notably, lactate derived from aspartate showed a large reduction, and in astrocytes, incorporation of labeled acetyl‐CoA into the TCA cycle was significantly reduced, Thus, astroCytes and cerebellar granule neurons differ in their handling of aspartates.
Abstract: The metabolism of [U-13C]aspartate was studied in cultured cortical astrocytes and cerebellar granule neurons in the presence of glucose and during inhibition of glycolysis. Redissolved, lyophilized cell extracts and incubation media were analyzed by 13C nuclear magnetic resonance spectroscopy for the determination of metabolites labeled from aspartate. Uniformly labeled lactate was prominent in control media of astrocytes and cerebellar granule neurons. In both cell types, aspartate entered the tricarboxylic acid (TCA) cycle, as shown by labeling patterns in glutamate and, in astrocytes, in glutamine. From the complex labeling patterns in aspartate in astrocytic perchloric acid extracts it was clear that acetylcoenzyme A (acetyl-CoA) derived from aspartate via oxaloacetate and pyruvate could enter the TCA cycle. Such "recycling," however, could not be detected in cerebellar granule neurons. Inhibition of glycolysis reduced aspartate uptake and metabolism in both cell types. Most notably, lactate derived from aspartate showed a large reduction, and in astrocytes, incorporation of labeled acetyl-CoA into the TCA cycle was significantly reduced. Thus, astrocytes and cerebellar granule neurons differ in their handling of aspartate. Furthermore, inhibition of glycolysis clearly affected aspartate metabolism by such cells.
35 citations