Badar-Goffer R S, Ben-Yoseph O, Bachelard H S, Morris P G
Department of Biochemistry, University of Cambridge, U.K.
Biochem J. 1992 Feb 15;282 ( Pt 1)(Pt 1):225-30. doi: 10.1042/bj2820225.
Time courses of incorporation of 13C from 13C-labelled glucose and/or acetate into the individual carbon atoms of amino acids, citrate and lactate in depolarized cerebral tissues were monitored by using 13C-n.m.r. spectroscopy. There was no change in the maximum percentage of 13C enrichments of the amino acids on depolarization, but the maxima were reached more rapidly, indicating that rates of metabolism in both glycolysis and the tricarboxylic acid cycle were accelerated. Although labelling of lactate and of citrate approached the theoretical maximum of 50%, labelling of the amino acids was always below 20%, suggesting that there is a metabolic pool or compartment that is inaccessible to exogenous substrates. Under resting conditions labelling of citrate and of glutamine from [1-13C]glucose was not detected, whereas both were labelled from [2-13C]acetate, which is considered to reflect glial metabolism. In contrast, considerable labelling of these two metabolites from [1-13C]glucose was observed in depolarized tissues, suggesting that the increased metabolism may be due to increased consumption of glucose by glial cells. The labelling patterns on depolarization from [1-13C]glucose alone and from both precursors [( 1-13C]glucose plus [2-13C]acetate) were similar, which also indicates that the changes are due to increased consumption of glucose rather than acetate.
利用¹³C核磁共振波谱法监测了¹³C标记的葡萄糖和/或乙酸盐中的¹³C掺入去极化脑组织中氨基酸、柠檬酸和乳酸的各个碳原子的时间进程。去极化时氨基酸的¹³C富集最大百分比没有变化，但达到最大值的速度更快，这表明糖酵解和三羧酸循环中的代谢速率均加快。尽管乳酸和柠檬酸的标记接近理论最大值50%，但氨基酸的标记始终低于20%，这表明存在一个外源性底物无法进入的代谢池或区室。在静息条件下，未检测到[1-¹³C]葡萄糖对柠檬酸和谷氨酰胺的标记，而两者均由[2-¹³C]乙酸盐标记，这被认为反映了胶质细胞的代谢。相反，在去极化组织中观察到[1-¹³C]葡萄糖对这两种代谢物有相当程度的标记，这表明代谢增加可能是由于胶质细胞对葡萄糖的消耗增加所致。仅由[1-¹³C]葡萄糖和由两种前体物质（[1-¹³C]葡萄糖加[2-¹³C]乙酸盐）去极化时的标记模式相似，这也表明变化是由于葡萄糖而非乙酸盐消耗增加所致。
