Davis R A, Boogaerts J R, Borchardt R A, Malone-McNeal M, Archambault-Schexnayder J
J Biol Chem. 1985 Nov 15;260(26):14137-44.
Hepatocytes obtained from rats fed for 3 days chow (control) or drinking water only (fasted) were used to examine how metabolic state affects lipogenesis, apolipoprotein synthesis, and the capacity to secrete de novo synthesized triacylglycerol. The secretion of triacylglycerol (mass and 3H-labeled via 3H2O incorporation) by both groups of cells was constant for 30 h. Moreover, cells from fasted rats secreted triacylglycerol at rates which were markedly reduced (mass -84%; 3H-labeled -91%). To assess the relative capacities of the two groups of hepatocytes to augment triacylglycerol secretion in response to stimulated lipogenesis, cells were incubated with increasing concentrations of glucose. Control cells responded to glucose by increasing equally the synthesis and secretion of [3H] triacylglycerol. When cells from fasted rats were challenged with glucose, triacylglycerol secretion was not increased. Rather, it accumulated intracellularly. Double-reciprocal plot analysis of the capacity to augment triacylglycerol secretion in response to glucose showed that cells from fasted rats had a greater than 10-fold decrease in V'max. Moreover, fasting changed the synthesis and secretion of apolipoproteins selectively: secretion of low molecular weight apo-B was decreased 50%, large molecular weight apo-B was unchanged, and apo-E was increased 2-4-fold. Analysis of the lipoproteins from both groups of cells on Bio-Gel A-50m showed that the very low density lipoprotein secreted by cells from fasted rats was smaller. In addition, all of the increased de novo synthesized apo-E secreted by cells from fasted rats eluted after the triacylglycerol-rich lipoproteins. The combined data show that: 1) the synthesis of individual very low density lipoprotein apolipoproteins is independently regulated, and 2) the synthesis (availability) of apo-B determines the capacity of the hepatocyte to assemble/secrete triacylglycerol-rich very low density lipoprotein.
从喂食3天普通饲料（对照）或仅饮用蒸馏水（禁食）的大鼠获取肝细胞，用于研究代谢状态如何影响脂肪生成、载脂蛋白合成以及分泌新合成三酰甘油的能力。两组细胞三酰甘油（质量以及通过掺入³H₂O进行³H标记）的分泌在30小时内保持恒定。此外，禁食大鼠的细胞分泌三酰甘油的速率显著降低（质量降低84%；³H标记降低91%）。为评估两组肝细胞在脂肪生成受刺激时增加三酰甘油分泌的相对能力，将细胞与浓度不断增加的葡萄糖一起孵育。对照细胞对葡萄糖的反应是同等程度地增加[³H]三酰甘油的合成与分泌。当用葡萄糖刺激禁食大鼠的细胞时，三酰甘油分泌并未增加，而是在细胞内积累。对葡萄糖刺激下增加三酰甘油分泌能力的双倒数作图分析表明，禁食大鼠的细胞V'max降低超过10倍。此外，禁食选择性地改变了载脂蛋白的合成与分泌：低分子量载脂蛋白B的分泌减少50%，高分子量载脂蛋白B不变，载脂蛋白E增加2至4倍。对两组细胞的脂蛋白在Bio-Gel A-50m上进行分析表明，禁食大鼠细胞分泌的极低密度脂蛋白较小。此外，禁食大鼠细胞分泌的所有增加的新合成载脂蛋白E在富含三酰甘油的脂蛋白之后洗脱。综合数据表明：1）单个极低密度脂蛋白载脂蛋白的合成是独立调节的；2）载脂蛋白B的合成（可用性）决定了肝细胞组装/分泌富含三酰甘油的极低密度脂蛋白的能力。
