Brooks K J, Kauppinen R A, Williams S R, Bachelard H S, Bates T E, Gadian D G
Division of Biochemistry, UMDS (St Thomas's Hospital Medical School), London, U.K.
Neuroscience. 1989;33(1):185-92. doi: 10.1016/0306-4522(89)90320-5.
[31P]- and [1H]Nuclear magnetic resonance spectroscopy were used to study metabolism in cortical brain slices in the guinea-pig during acute exposure to pathophysiological concentrations of ammonia. Intracellular acidification, measured from the chemical shift of endogenous inorganic phosphate, was observed without any change in cellular energy status or concentrations of lactate, glutamate and glutamine. The initial acidification, which developed over a period of 9 min appeared to be heterogeneous, on the basis of a splitting of the inorganic phosphate resonance in a number of experiments, corresponding to pH changes of 0.07 and 0.27 pH units. Subsequently a homogeneous acidification, of 0.15 pH units, developed by 23 min following exposure to ammonia. Intracellular pH recovered within 6 min after discontinuation of the ammonia load. In the absence of external bicarbonate, intracellular pH was 0.12 units more acidic than in the bicarbonate buffer and ammonia caused a further acidification by 0.16 units. When glutamine synthase inhibitor, methionine sulphoximine, was added, there was a slow fall in intracellular pH. Under these conditions, subsequent addition of ammonia failed to cause acidification directly. Thus acute elevation of ammonia does not lead to a change in cerebral high-energy phosphate or lactate metabolism, but may be associated with a fall in cortical intracellular pH.
利用[31P]和[1H]核磁共振波谱法研究豚鼠大脑皮质切片在急性暴露于病理生理浓度氨期间的代谢情况。通过内源性无机磷酸盐的化学位移测量细胞内酸化，结果显示细胞能量状态以及乳酸、谷氨酸和谷氨酰胺浓度均未发生任何变化。在一些实验中，根据无机磷酸盐共振峰的分裂情况，最初在9分钟内出现的酸化似乎是不均匀的，对应的pH变化为0.07和0.27个pH单位。随后，在暴露于氨后23分钟时出现了0.15个pH单位的均匀酸化。在停止氨负荷后6分钟内细胞内pH恢复正常。在没有外部碳酸氢盐的情况下，细胞内pH比在碳酸氢盐缓冲液中酸性高0.12个单位，氨导致进一步酸化0.16个单位。当添加谷氨酰胺合成酶抑制剂甲硫氨酸亚砜亚胺时，细胞内pH缓慢下降。在这些条件下，随后添加氨未能直接导致酸化。因此，氨的急性升高不会导致脑高能磷酸盐或乳酸代谢的变化，但可能与皮质细胞内pH下降有关。
