Uptake of monosaccharides by guinea-pig cerebral-cortex slices.
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ABSTRACT:
SUBMITTER: Joanny P
PROVIDER: S-EPMC1187716 | biostudies-other | 1969 Apr
REPOSITORIES: biostudies-other
Similar Datasets
Project description:1. When guinea-pig cerebral-cortex slices were incubated with [U-(14)C]glutamate as substrate, the specific radioactivities of the citric acid-cycle intermediates were lower than that of the aspartate isolated from the same vessels. 2. Aspartate was significantly labelled when [5-(14)C]glutamate was used as substrate and the aspartate contained almost no label when [1-(14)C]glutamate was present as substrate. 3. When specifically labelled glutamate was used as substrate, the label was found in the isolated aspartate in the position that would be predicted by citric acid-cycle mechanisms. 4. The results are consistent with the theory of ;compartmentation' of amino acid metabolism.
| S-EPMC1198617 | biostudies-other
Project description:1. Starvation did not affect the rates of glucose utilization or lactate formation by guinea-pig cerebral cortex slices. 2. Palmitate (1mm), butyrate (5mm) or acetoacetate (5mm) did not affect glucose utilization or lactate formation by cerebral cortex slices from guinea pigs starved for 48hr. 3. dl-beta-Hydroxybutyrate (10mm) increased the formation of lactate without affecting glucose utilization by cerebral cortex slices from guinea pigs starved for 48hr. This implies that beta-hydroxybutyrate decreased the rate of glucose oxidation. 4. Metabolism of added ketone bodies can account for 20-40% of observed rates of oxygen consumption. 5. Lactate or pyruvate (5mm) decreased the rates of glucose utilization by guinea-pig cerebral cortex slices.
| S-EPMC1270614 | biostudies-other
Project description:The kinetics of the influx and efflux of radioactive l-glycine was studied in slices of rat cerebral cortex. The influx showed saturation kinetics and was inhibited by l-alanine. Influx was dependent on the presence of Na(+) ions and a metabolizable substrate. The efflux of glycine was accelerated by alanine. It was concluded that carrier-mediated facilitated diffusion was the mechanism of glycine uptake by, and efflux from, cerebral slices.
| S-EPMC1178048 | biostudies-other
Project description:1. Cerebral-cortex slices from rat brain, loaded with labelled l-glutamate as a result of aerobic incubation with labelled glucose, lost less than 15% of this glutamate on subsequent incubation in the presence of unlabelled glucose and l-glutamate. This indicates that very little exchange occurs between extracellular l-glutamate and glutamate accumulated in the neurons as a result of glucose metabolism. 2. Slices, loaded with labelled l-glutamate as a result of aerobic incubation in a medium containing unlabelled glucose and labelled l-glutamate, lost more than half of this glutamate on subsequent incubation in the presence of unlabelled l-glutamate. This indicates that exchange occurs between extracellular glutamate and glutamate accumulated in brain slices as a result of its uptake from the incubation medium. 3. Evidence was obtained suggesting that only a part of the glutamate, accumulated in brain slices as a result of its uptake from an incubation medium containing both glucose and l-glutamate, entered the neurons; apparently almost all the rest entered the glia. 4. It is concluded that the slices contain a pool of glutamate, derived from glucose and located in the neurons, which is poorly exchangeable with extracellular glutamate, and another pool of glutamate, derived from extracellular glutamate and located in the glia, which is freely exchangeable with extracellular glutamate.
| S-EPMC1174000 | biostudies-other
Project description:1. The effect of various agents on the turnover of protein-bound phosphorus in respiring slices of cerebral cortex was studied. 2. Confirming previous work turnover was increased by the application of electrical pulses for 10s to the tissue. 3. Turnover was also increased by exposure of the slices for 10min to noradrenaline (0.5mm), 5-hydroxytryptamine (1mum) and histamine (0.1mm). 4. When slices were stimulated by electrical pulses in the presence of histamine the increase in turnover was the sum of the responses given by each agent above, suggesting that different phosphorylating systems were involved. 5. Tetrodotoxin (0.5mum) blocked the increased turnover due to electrical pulses, but not that due to histamine. Tetrodotoxin also prevented the increase in tissue cyclic AMP content caused by the application of electrical pulses. 6. Phosphoprotein turnover was not affected by adenosine, despite the increase in tissue cyclic AMP content given by this agent. 7. Adenosine blocked the phosphoprotein response to histamine, but did not affect the response to electrical pulses. 8. The results are discussed in relation to the hypothesis that the stimulation of protein phosphorus turnover by electrical pulses is secondary to the release of cyclic AMP in the tissue.
| S-EPMC1177611 | biostudies-other
Project description:Vocal communication is an important aspect of guinea pig behaviour and a large contributor to their acoustic environment. We postulated that some cortical areas have distinctive roles in processing conspecific calls. In order to test this hypothesis we presented exemplars from all ten of their main adult vocalizations to urethane anesthetised animals while recording from each of the eight areas of the auditory cortex. We demonstrate that the primary area (AI) and three adjacent auditory belt areas contain many units that give isomorphic responses to vocalizations. These are the ventrorostral belt (VRB), the transitional belt area (T) that is ventral to AI and the small area (area S) that is rostral to AI. Area VRB has a denser representation of cells that are better at discriminating among calls by using either a rate code or a temporal code than any other area. Furthermore, 10% of VRB cells responded to communication calls but did not respond to stimuli such as clicks, broadband noise or pure tones. Area S has a sparse distribution of call responsive cells that showed excellent temporal locking, 31% of which selectively responded to a single call. AI responded well to all vocalizations and was much more responsive to vocalizations than the adjacent dorsocaudal core area. Areas VRB, AI and S contained units with the highest levels of mutual information about call stimuli. Area T also responded well to some calls but seems to be specialized for low sound levels. The two dorsal belt areas are comparatively unresponsive to vocalizations and contain little information about the calls. AI projects to areas S, VRB and T, so there may be both rostral and ventral pathways for processing vocalizations in the guinea pig.
| S-EPMC3520958 | biostudies-literature
Project description:Inhibition of receptor-coupled adenylate cyclase by hormones is proposed to be associated with GTP hydrolysis. Since adenosine inhibits cerebral-cortical adenylate cyclase via A1 adenosine receptors, the present study attempts to verify this mechanism for A1-selective adenosine derivatives. In guinea-pig cortical membranes N6-(phenylisopropyl)adenosine (PIA) increased the Vmax. of the low-Km GTPase, with an EC50 (concentration causing 50% of maximal stimulation) of about 0.1 microM, and the stimulatory effect was competitively antagonized by 5 microM-8-phenyltheophylline. The rank order of potency of the stereoisomers of PIA and of 5-(N-ethylcarboxamido)adenosine (NECA) to stimulate GTPase correlated with their ability to inhibit adenylate cyclase activity (R-PIA greater than NECA greater than S-PIA). Competition binding studies with (-)-N6- ([125I]iodo-4-hydroxyphenylisopropyl)adenosine suggest that adenylyl imidodiphosphate (p[NH]ppA), an essential component of the GTPase assay system, is a more potent A1-receptor agonist than ATP, with an IC50 (concentration giving half-maximal displacement of radioligand binding) of 7.9 microM. On the basis of the p[NH]ppA concentration used in the GTPase assay (1.25 mM), enzyme stimulation by adenosine seems to be highly underestimated. Nevertheless, adenosine-induced GTP hydrolysis reflects an increased turnover of guanine nucleotides at the Ni regulatory site and appears to be a crucial step in the sequence of events processing the inhibitory signal to adenylate cyclase.
| S-EPMC1152908 | biostudies-other
Project description:1. Hexokinase activities were estimated in primary subcellular fractions from guinea-pig cerebral cortex and in sucrose-density-gradient subfractions of the mitochondrial and microsomal fractions. 2. Appreciable activities were observed in mitochondrial, microsomal and soluble fractions. The activity in the mitochondrial fraction was associated with the mitochondria rather than with myelin or nerve endings and that in the microsomal fraction was associated with membrane fragments. 3. Most of the mitochondrial activity was extracted in soluble form by osmotic ;shock'. The activity of the mitochondrial extract differed from the soluble activity in kinetic properties and in electrophoretic behaviour. 4. No evidence was obtained for the presence of a high-K(m) glucokinase in the brain. 5. The results are discussed in terms of relevance to considerations of glucose utilization by the brain.
| S-EPMC1270574 | biostudies-other
Project description:1. Intracellular concentrations of intermediates and cofactors of glycolysis were measured in guinea-pig cerebral cortex slices incubated under varying conditions. 2. Comparison of mass-action ratios with apparent equilibrium constants for the reactions of glycolysis showed that hexokinase, phosphofructokinase and pyruvate kinase catalyse reactions generally far from equilibrium, whereas phosphoglucose isomerase, aldolase, phosphoglycerate kinase, phosphoglycerate mutase, enolase, adenlyate kinase and creatine phosphokinase are generally close to equilibrium. The possibility that glyceraldehyde 3-phosphate dehydrogenase may catalyse a ;non-equilibrium' reaction is discussed. 3. Correlation of changes in concentrations of substrates for enzymes catalysing ;non-equilibrium' reactions with changes in rates of glycolysis caused by alteration of the conditions of incubation showed that hexokinase, phosphofructokinase, pyruvate kinase and possibly glyceraldehyde 3-phosphate dehydrogenase are subject to metabolic control in cerebral cortex slices. 4. It is suggested that the glycolysis is controlled by two regulatory systems, the hexokinase-phosphofructokinase system and the glyceraldehyde 3-phosphate dehydrogenase-pyruvate kinase system. These are discussed. 5. It is concluded that the rate of glycolysis in guinea-pig cerebral cortex slices is limited either by the rate of glucose entry into the slices or by the hexokinase-phosphofructokinase system. 6. It is concluded that addition of 0.1mm-ouabain to guinea-pig cerebral cortex slices causes inhibition of either glyceraldehyde 3-phosphate dehydrogenase or phosphoglycerate kinase or both, in a manner independent of the known action of ouabain on the sodium- and potassium-activated adenosine triphosphatase.
| S-EPMC1270615 | biostudies-other
Project description:The uptake of radioactive l-phenylalanine and l-tyrosine into the tissue water of rat brain cerebral cortex slices was shown to have saturation kinetics. The apparent K(m) for the uptake of l-phenylalanine was 0.86mm and for l-tyrosine was 1.64mm; for phenylalanine the apparent V(max.) value was 0.64mumol/min per ml of tissue water, and for l-tyrosine it was 0.98mumol/min per ml of tissue water. The accumulation of the two amino acids by the tissue was depressed in the absence of O(2), at 0 degrees C, or in the presence of metabolic inhibitors. The influxes and effluxes of both l-isomers were more rapid than those of the d-isomers. Competition between these two amino acids and each with l-tryptophan in respect of uptake into tissue water was shown. Their rates of influx were faster, and rates of efflux were slower, in the presence than in the absence of Na(+). It was concluded that these amino acids were taken up by active transport via a carrier mechanism.
| S-EPMC1165926 | biostudies-other