STIMULATION OF GLYCOLYSIS BY HISTIDINE BUFFERS IN MAMMALIAN LIVER DURING COLD HYPOXIA

This study was designed to address the reasons why glycolysis in mamma lian liver is unable to function more efficiently during periods of co ld hypoxia. Our hypothesis was that control of intracellular pH, by us e of amino acid buffers with high pK(a) values, would allow prolonged flux through glycolysis and better maintenance of liver high-energy ad enine 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 an aerobic endproduct (lactate) were investigated during cold hypoxia usi ng rat livers to model the mammalian system. The transition to anaerob ic metabolism was apparent by an immediate rise in lactate levels upon entry into cold hypoxia. By 10-14 h hypoxia, contents of the endprodu ct had increased by 10, 13.5, and 14.5 mu mol/g in buffers containing 90 and 180 mM. histidine and 90 mM carnosine, respectively. As well, A TP, total adenylate contents, and ''energy charge'' ratios exhibited a rapid decline from initial values of 2.3-3.3 mu mol/g, 4.3-5.5 mu mol /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 m ost positive maintenance of adenylate levels, followed closely by 90 m M 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 i n a solution of minor buffering capacity (a citrate-based solution) ov er the same time period. The data support the hypothesis that glycolyt ic flux and cellular energetics can be maintained by the inclusion of efficient buffering agents during periods of cold hypoxia. (C) 1995 Ac ademic Press, Inc.