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Water uptake and energy metabolism in brain slices from the rat.

ABSTRACT: 1. Exchange of (3)H(2)O with H(2)O takes place rapidly in incubated rat brain slices but at a lower rate in slices from infant brain than from adult brain. The temperature coefficient (Q(10)) of the exchange process, between 37 and 4 degrees C, is 1.76 with infant brain and 1.26 with adult brain. The exchange process is unaffected by the presence of ouabain or 2,4-dinitrophenol. 2. An approximately linear relationship exists between water uptake and the concentration of ATP in the incubated slices in the presence of various concentrations of glucose. Little or no change occurs in water uptake and ATP concentration in the presence of a glucose concentration exceeding 3mm. A linear relationship also exists between the water uptake and ATP concentration in the presence of 10mm-glucose and various concentrations of sodium l-glutamate but the line is parallel to that found with changed glucose concentrations and shifted in the direction of increased water uptake. A similar parallel relationship exists between water uptake and ATP concentration in the presence of 2,4-dinitrophenol, but the amount of water uptake is significantly smaller in the presence of 2,4-dinitrophenol than in its absence. 3. Copper chloride (0.3mm) or mercuric chloride (0.3mm) both increase water uptake and diminish the ATP concentration in slices. Sodium malonate (2mm) or sodium d-glutamate (10mm) has similar effects. 4. Substances, or conditions, affecting water uptake in incubated brain slices may be divided roughly into two classes in accordance with their effects on adenosine triphosphatase and membrane permeability, but there may be considerable lack of specificity.

SUBMITTER: Okamoto K

PROVIDER: S-EPMC1179565 | biostudies-other | 1970 Nov

REPOSITORIES: biostudies-other

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Project description:1. The development of pyruvate dehydrogenase and citrate synthase activity in rat brain mitochondria was studied. Whereas the citrate synthase activity starts to increase at about 8 days after birth, that of pyruvate dehydrogenase starts to increase at about 15 days. Measurements of the active proportion of pyruvate dehydrogenase during development were also made. 2. The ability of rat brain mitochondria to oxidize pyruvate follows a similar developmental pattern to that of the pyruvate dehydrogenase. However, the ability to oxidize 3-hydroxybutyrate shows a different developmental pattern (maximal at 20 days and declining by half in the adult), which is compatible with the developmental pattern of the ketone-body-utilizing enzymes. 3. The developmental pattern of both the soluble and the mitochondrially bound hexokinase of rat brain was studied. The total brain hexokinase activity increases markedly at about 15 days, which is mainly due to an increase in activity of the mitochondrially bound form, and reaches the adult situation (approx. 70% being mitochondrial) at about 30 days after birth. 4. The release of the mitochondrially bound hexokinase under different conditions by glucose 6-phosphate was studied. There was insignificant release of the bound hexokinase in media containing high KCl concentrations by glucose 6-phosphate, but in sucrose media half-maximal release of hexokinase was achieved by 70mum-glucose 6-phosphate 5. The production of glucose 6-phosphate by brain mitochondria in the presence of Mg(2+)+glucose was demonstrated, together with the inhibition of this by atractyloside. 6. The results are discussed with respect to the possible biological significance of the similar developmental patterns of pyruvate dehydrogenase and the mitochondrially bound kinases, particularly hexokinase, in the brain. It is suggested that this association may be a mechanism for maintaining an efficient and active aerobic glycolysis which is necessary for full neural expression.

Project description:Acetyl-L-carnitine (ALCAR) is an endogenous metabolic intermediate that facilitates the influx and efflux of acetyl groups across the mitochondrial inner membrane. Exogenously administered ALCAR has been used as a nutritional supplement and also as an experimental drug with reported neuroprotective properties and effects on brain metabolism. The aim of this study was to determine oxidative metabolism of ALCAR in the immature rat forebrain. Metabolism was studied in 21-22 day-old rat brain at 15, 60 and 120 min after an intraperitoneal injection of [2-(13)C]acetyl-L-carnitine. The amount, pattern, and fractional enrichment of (13)C-labeled metabolites were determined by ex vivo(13)C-NMR spectroscopy. Metabolism of the acetyl moiety from [2-(13)C]ALCAR via the tricarboxylic acid cycle led to incorporation of label into the C4, C3 and C2 positions of glutamate (GLU), glutamine (GLN) and GABA. Labeling patterns indicated that [2-(13)C]ALCAR was metabolized by both neurons and glia; however, the percent enrichment was higher in GLN and GABA than in GLU, demonstrating high metabolism in astrocytes and GABAergic neurons. Incorporation of label into the C3 position of alanine, both C3 and C2 positions of lactate, and the C1 and C5 positions of glutamate and glutamine demonstrated that [2-(13)C]ALCAR was actively metabolized via the pyruvate recycling pathway. The enrichment of metabolites with (13)C from metabolism of ALCAR was highest in alanine C3 (11%) and lactate C3 (10%), with considerable enrichment in GABA C4 (8%), GLN C3 (approximately 4%) and GLN C5 (5%). Overall, our (13)C-NMR studies reveal that the acetyl moiety of ALCAR is metabolized for energy in both astrocytes and neurons and the label incorporated into the neurotransmitters glutamate and GABA. Cycling ratios showed prolonged cycling of carbon from the acetyl moiety of ALCAR in the tricarboxylic acid cycle. Labeling of compounds formed from metabolism of [2-(13)C]ALCAR via the pyruvate recycling pathway was higher than values reported for other precursors and may reflect high activity of this pathway in the developing brain. This is, to our knowledge, the first study to determine the extent and pathways of ALCAR metabolism for energy and neurotransmitter biosynthesis in the brain.

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Water uptake and energy metabolism in brain slices from the rat.

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