Tosh D, Beresford G, Agius L
Department of Medicine, University of Newcastle upon Tyne, UK.
Biochim Biophys Acta. 1994 Nov 10;1224(2):205-12. doi: 10.1016/0167-4889(94)90192-9.
The conversion of glucose to glycogen by direct and indirect pathways was determined from the incorporation of [6-3H,U-14C]glucose into glycogen in hepatocyte cultures isolated from fed, fasted or fasted-refed rats. Mercaptopicolinate, an inhibitor of phosphoenolpyruvate carboxykinase (PEPCK) was used to determine the extent by which 6-tritium is lost by mechanisms not involving flux through PEPCK. Glucose conversion to glycogen was lower in hepatocytes from fasted and higher in hepatocytes from fasted-refed rats than in hepatocytes from rats fed ad libitum. Insulin increased glycogen synthesis in hepatocytes from all nutritional states, and it decreased the 3H/14C ratio incorporated into glycogen. This increased loss of 6-tritium was only in part mercaptopicolinate-sensitive. Lactate and pyruvate (2 mM + 0.2 mM) increased glycogen deposition, largely by stimulation of glucose conversion to glycogen by the direct pathway. Insulin-induced glucokinase mRNA expression was higher in hepatocytes from fed than from fasted or refed rats whereas PEPCK mRNA expression was lowest in hepatocytes from fasted-refed rats. Hepatocyte cultures derived from different nutritional states express differences in glycogen synthesis from glucose by direct and indirect pathways as well as differences in the extent by which pyruvate cycling accounts for loss of 6-tritium.
通过将[6-³H，U-¹⁴C]葡萄糖掺入从喂食、禁食或禁食后再喂食的大鼠分离的肝细胞培养物中的糖原中，来测定葡萄糖通过直接和间接途径转化为糖原的情况。使用磷酸烯醇式丙酮酸羧激酶（PEPCK）抑制剂巯基吡啶甲酸盐来确定6-³H通过不涉及PEPCK通量的机制损失的程度。与自由进食大鼠的肝细胞相比，禁食大鼠的肝细胞中葡萄糖向糖原的转化较低，禁食后再喂食大鼠的肝细胞中葡萄糖向糖原的转化较高。胰岛素增加了所有营养状态下肝细胞中的糖原合成，并降低了掺入糖原中的³H/¹⁴C比值。这种6-³H损失的增加仅部分对巯基吡啶甲酸盐敏感。乳酸和丙酮酸（2 mM + 0.2 mM）增加了糖原沉积，主要是通过直接途径刺激葡萄糖转化为糖原。胰岛素诱导的葡萄糖激酶mRNA表达在喂食大鼠的肝细胞中高于禁食或再喂食大鼠的肝细胞，而PEPCK mRNA表达在禁食后再喂食大鼠的肝细胞中最低。来自不同营养状态的肝细胞培养物在通过直接和间接途径从葡萄糖合成糖原方面存在差异，以及丙酮酸循环导致6-³H损失的程度方面也存在差异。
