The metabolism of glucose 6-phosphate by mammalian cerebral cortex in vitro.
1. The metabolism of glucose 6-phosphate in rat cerebral-cortex slices in vitro was compared with that of glucose. It was found that a glucose 6-phosphate concentration of 25mm was required to achieve maximal oxygen uptake rates and ATP concentrations, whereas only 2mm-glucose was required. 2. When 25mm-[U-(14)C]glucose 6-phosphate was used as substrate, the pattern of labelling of metabolites was found to be quantitatively and qualitatively similar to the pattern found with 10mm-[U-(14)C]glucose, except that incorporation into [(14)C]lactate was decreased, and significant amounts of [(14)C]glucose and [(14)C]mannose phosphate and [(14)C]fructose phosphate were formed. 3. Unlabelled glucose (10mm) caused a tenfold decrease in the incorporation of 25mm-[U-(14)C]glucose 6-phosphate into all metabolites except [(14)C]glucose and [(14)C]mannose phosphate and [(14)C]fructose phosphate. In contrast, unlabelled glucose 6-phosphate (25mm) had no effect on the metabolism of 10mm-[U-(14)C]glucose other than to increase markedly the incorporation into, and amount of, [(14)C]lactate, the specific radioactivity of this compound remaining approximately the same. 4. The effect of glucose 6-phosphate in increasing lactate formation from glucose was found to occur also with a number of other phosphate esters and with inorganic phosphate. Further investigation indicated that the effect was probably due to binding of medium calcium by the phosphate moiety, thereby de-inhibiting glucose uptake. 5. Incubations carried out in a high-phosphate high-potassium medium gave a pattern of metabolism similar to that found when slices were subjected to depolarizing conditions. Tris-buffered medium gave similar results to bicarbonate-buffered saline, except that it allowed much less lactate formation from glucose. 6. Part of the glucose formed from glucose 6-phosphate was extracellular and was produced at a rate of 12mumol/h per g of tissue in Krebs tris medium when glycolysis was blocked. The amount formed was much less when 25mm-P(i) or 26mm-HCO(3) (-) was present, the latter being in the absence of tris. 7. Glucose 6-phosphate also gave rise to an intracellular glucose pool, whereas no intracellular glucose was detectable when glucose was the substrate.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002021:Buffers; D002118:Calcium; D002247:Carbon Isotopes; D002540:Cerebral Cortex / Q000378:metabolism*; D002854:Chromatography, Paper; D005260:Female; D005636:Fructosephosphates / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D005958:Glucosephosphates / Q000378:metabolism; D006600:Hexosephosphates / Q000378:metabolism*; D066298:In Vitro Techniques; D007444:Inulin / Q000378:metabolism; D007785:Lactose / Q000378:metabolism; D008297:Male; D008358:Mannose / Q000378:metabolism; D010101:Oxygen Consumption; D011188:Potassium; D051381:Rats
D002021:Buffers; D002247:Carbon Isotopes; D005636:Fructosephosphates; D005958:Glucosephosphates; D006600:Hexosephosphates; D000255:Adenosine Triphosphate; D007444:Inulin; D005947:Glucose; D007785:Lactose; D008358:Mannose; D011188:Potassium; D002118:Calcium