Churchill T A, Green C J, Fuller B J
University Department of Surgery, Royal Free Hospital School of Medicine, London, United Kingdom.
Arch Biochem Biophys. 1995 Jun 20;320(1):43-50. doi: 10.1006/abbi.1995.1340.
This study was designed to address the reasons why glycolysis in mammalian liver is unable to function more efficiently during periods of cold hypoxia. Our hypothesis was that control of intracellular pH, by use of amino acid buffers with high pKa values, would allow prolonged flux through glycolysis and better maintenance of liver high-energy adenine nucleotide pool. The effects of two concentrations of histidine (90 and 180 mM) and one of carnosine (90 mM), a histidyl dipeptide, on energy metabolism and levels of glycolytic substrate (glucose) and anaerobic endproduct (lactate) were investigated during cold hypoxia using rat livers to model the mammalian system. The transition to anaerobic metabolism was apparent by an immediate rise in lactate levels upon entry into cold hypoxia. By 10-14 h hypoxia, contents of the endproduct had increased by 10, 13.5, and 14.5 mumol/g in buffers containing 90 and 180 mM histidine and 90 mM carnosine, respectively. As well, ATP, total adenylate contents, and "energy charge" ratios exhibited a rapid decline from initial values of 2.3-3.3 mumol/g, 4.3-5.5 mumol/g, and 0.64-0.75, respectively, over the first 2-4 h of cold hypoxia. With respect to efficacy, the 180 mM histidine buffer exhibited the most positive maintenance of adenylate levels, followed closely by 90 mM carnosine, and finally 90 mM histidine as the least effective of the three buffers. Nevertheless, all three buffers examined in this study showed positive effects compared to similarly treated livers stored in a solution of minor buffering capacity (a citrate-based solution) over the same time period. The data support the hypothesis that glycolytic flux and cellular energetics can be maintained by the inclusion of efficient buffering agents during periods of cold hypoxia.
本研究旨在探讨哺乳动物肝脏糖酵解在冷缺氧期间无法更高效发挥功能的原因。我们的假设是，通过使用具有高pKa值的氨基酸缓冲剂来控制细胞内pH值，将能够使糖酵解通量延长，并更好地维持肝脏高能腺嘌呤核苷酸池。在冷缺氧期间，使用大鼠肝脏作为哺乳动物系统的模型，研究了两种浓度的组氨酸（90和180 mM）以及一种肌肽（90 mM，一种组氨酸二肽）对能量代谢以及糖酵解底物（葡萄糖）和厌氧终产物（乳酸）水平的影响。进入冷缺氧状态后，乳酸水平立即升高，这表明向无氧代谢的转变很明显。到缺氧10 - 14小时时，在含有90 mM和180 mM组氨酸以及90 mM肌肽的缓冲液中，终产物的含量分别增加了10、13.5和14.5 μmol/g。同样，在冷缺氧的最初2 - 4小时内，ATP、总腺苷酸含量和“能荷”比值分别从初始值2.3 - 3.3 μmol/g、4.3 - 5.5 μmol/g和0.64 - 0.75迅速下降。就功效而言，180 mM组氨酸缓冲液对腺苷酸水平的维持最为积极，其次是90 mM肌肽，最后是90 mM组氨酸，是三种缓冲液中效果最差的。然而，与在相同时间段内保存在缓冲能力较弱的溶液（一种柠檬酸盐溶液）中的类似处理肝脏相比，本研究中检测的所有三种缓冲液都显示出积极效果。这些数据支持了这样的假设，即在冷缺氧期间，通过加入高效缓冲剂可以维持糖酵解通量和细胞能量学。
