Abumrad N A, Forest C, Regen D M, Barnella U S, Melki S A
Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Am J Physiol. 1991 Jul;261(1 Pt 1):E76-86. doi: 10.1152/ajpendo.1991.261.1.E76.
Incorporation of [3H]oleate and [14C]glucose into cellular lipids was studied in the preadipose cell line BFC-1 to determine flux changes that accompany the adipose conversion process. Dilution of oleate by intracellular fatty acids (FA) was estimated from the 3H/14C incorporation ratios and from relating steady-state radioactivity in diglycerides to their measured cellular levels. The data indicated that exogenous FA mixed with less than 1% of endogenous FA on its pathway to esterification. Conversion of preadipocytes to adipocytes increased uptake of FA and glucose by approximately 3-fold and synthesis of diglycerides and triglycerides by 5- and 16-fold, respectively, with little if any increase of phospholipid synthesis. A 50% drop in 3H/14C incorporation ratio indicated a doubling of the rate at which endogenous FA mixed with the exogenous FA that had entered the cell. Adipocytes compared with preadipocytes exhibited a 50% greater cell diameter and a doubling of intracellular water volume and of protein and phospholipid levels, reflecting cellular enlargement consequent to the arrest of cell division that precedes adipose conversion. Diglyceride levels were also increased in adipocytes, however, since their turnover was fast, as indicated by rapid equilibration of diglyceride labeling; the increase reflected changes in their relative rates of synthesis and disposal. Diglyceride levels related to cell phospholipid, and other indexes of cell size remained constant. This indicated that the supply of diglycerides was tightly coupled to the synthesis of triglycerides and phospholipids, which suggested feedback regulation of diglyceride formation. The studies provide a methodological approach to measurement and interpretation of rates of lipid deposition in cultured cells.
为了确定伴随脂肪转化过程的通量变化，我们在脂肪前体细胞系BFC - 1中研究了[3H]油酸和[14C]葡萄糖掺入细胞脂质的情况。根据3H/14C掺入率以及甘油二酯中的稳态放射性与其测量的细胞水平之间的关系，估算细胞内脂肪酸（FA）对油酸的稀释作用。数据表明，外源性FA在酯化途径中与不到1%的内源性FA混合。前脂肪细胞向脂肪细胞的转化使FA和葡萄糖的摄取分别增加了约3倍，甘油二酯和甘油三酯的合成分别增加了5倍和16倍，而磷脂合成几乎没有增加。3H/14C掺入率下降50%表明进入细胞的外源性FA与内源性FA混合的速率增加了一倍。与前脂肪细胞相比，脂肪细胞的细胞直径大50%，细胞内水体积、蛋白质和磷脂水平增加了一倍，这反映了脂肪转化前细胞分裂停止导致的细胞增大。然而，脂肪细胞中的甘油二酯水平也增加了，因为其周转很快，甘油二酯标记的快速平衡表明了这一点；这种增加反映了其合成和处置相对速率的变化。与细胞磷脂相关的甘油二酯水平以及其他细胞大小指标保持不变。这表明甘油二酯的供应与甘油三酯和磷脂的合成紧密相关，这提示了对甘油二酯形成的反馈调节。这些研究为测量和解释培养细胞中脂质沉积速率提供了一种方法学途径。
