The metabolism of malate by cultured rat brain astrocytes

• Published in: Neurochemical research 1990-12, Vol.15 (12), p.1211-1220
• Main Authors: MCKENNA, M. C, TILDON, J. T, COUTO, R, STEVENSON, J. H, CAPRIO, F. J
• Format: Article
• Language: English
• Subjects: 550501 - Metabolism- Tracer Techniques; ANIMAL CELLS; ANIMALS; Animals, Newborn; Astrocytes - metabolism; BASIC BIOLOGICAL SCIENCES; Biological and medical sciences; BODY; BRAIN; Brain - metabolism; CARBON 14 COMPOUNDS; CARBON COMPOUNDS; CARBON DIOXIDE; Carbon Dioxide - analysis; CARBON OXIDES; Carbon Radioisotopes; CARBOXYLIC ACIDS; Cell Compartmentation; CELL CULTURES; Cells, Cultured; CENTRAL NERVOUS SYSTEM; CHALCOGENIDES; Citric Acid Cycle; ELECTRON TRANSFER; Energy Metabolism; Fundamental and applied biological sciences. Psychology; HYDROXY ACIDS; Isolated neuron and nerve. Neuroglia; ISOTOPE APPLICATIONS; Kinetics; LABELLED COMPOUNDS; Malates - metabolism; MALIC ACID; MAMMALS; METABOLISM; Models, Biological; NERVE CELLS; NERVOUS SYSTEM; ORGANIC ACIDS; ORGANIC COMPOUNDS; ORGANS; OXIDES; OXYGEN COMPOUNDS; RATS; RODENTS; SOMATIC CELLS; TRACER TECHNIQUES; VERTEBRATES; Vertebrates: nervous system and sense organs
• ISSN: 0364-3190; 1573-6903
• DOI: 10.1007/BF01208582

Since malate is known to play an important role in a variety of functions in the brain including energy metabolism, the transfer of reducing equivalents and possibly metabolic trafficking between different cell types; a series of biochemical determinations were initiated to evaluate the rate of 14CO2 production from L-[U-14C]malate in primary cultures of rat brain astrocytes. The 14CO2 production from labeled malate was almost totally suppressed by the metabolic inhibitors rotenone and antimycin A suggesting that most of malate metabolism was coupled to the electron transport system. A double reciprocal plot of the 14CO2 production from the metabolism of labeled malate revealed biphasic kinetics with two apparent Km and Vmax values suggesting the presence of more than one mechanism of malate metabolism in these cells. Subsequent experiments were carried out using 0.01 mM and 0.5 mM malate to determine whether the addition of effectors would differentially alter the metabolism of high and low concentrations of malate. Effectors studied included compounds which could be endogenous regulators of malate metabolism and metabolic inhibitors which would provide information regarding the mechanisms regulating malate metabolism. Both lactate and aspartate decreased 14CO2 production from 0.01 mM and 0.5 mM malate equally. However, a number of effectors were identified which selectively altered the metabolism of 0.01 mM malate including aminooxyacetate, furosemide, N-acetylaspartate, oxaloacetate, pyruvate and glucose, but had little or no effect on the metabolism of 0.5 mM malate. In addition, alpha-ketoglutarate and succinate decreased 14CO2 production from 0.01 mM malate much more than from 0.5 mM malate. In contrast, a number of effectors altered the metabolism of 0.5 mM malate more than 0.01 mM. These included methionine sulfoximine, glutamate, malonate, alpha-cyano-4-hydroxycinnamate and ouabain. Both the biphasic kinetics and the differential action of many of the effectors on the 14CO2 production from 0.01 mM and 0.5 mM malate provide evidence for the presence of more than one pool of malate metabolism in cultured rat brain astrocytes.