Metabolism of the lipoprotein secreted by eel hepatocytes cultured primarily.

1.培养的鳗鱼肝细胞合成和分泌唯一的一种脂蛋白，即极低密度脂蛋白。虽然鳗鱼血清中存在两种主要的脂蛋白，即极低密度脂蛋白和高密度脂蛋白，但鳗鱼肝细胞不合成和分泌高密度脂蛋白。2.极低密度脂蛋白的特征。(1)极低密度脂蛋白的化学成分。极低密度脂蛋白中肌蛋白、三酰甘油、游离胆固醇、胆固醇酯和磷脂的含量分别为12、69、3.6、0.4和14%。(2)极低密度脂蛋白的载脂蛋白。极低密度脂蛋白的主要载脂蛋白是载脂蛋白A和载脂蛋白B。与哺乳动物肝脏分泌的极低密度脂蛋白最不同的是，哺乳动物分泌的极低密度脂蛋白不含载脂蛋白A作为主要载脂蛋白。(3)极低密度脂蛋白的分泌速率：培养的鳗鱼肝细胞分泌极低密度脂蛋白的速率为3.79×1.51微克/毫克细胞蛋白/小时(n=6)。这一数值是人肝细胞分泌极低密度脂蛋白速率的10倍。3.胰岛素和血清脂蛋白的影响。(1)胰岛素的作用。胰岛素抑制极低密度脂蛋白的分泌，并抑制14C-亮氨酸和14C-醋酸酯进入极低密度脂蛋白。(2)血清极低密度脂蛋白的影响。当血清VLDL加入鳗鱼肝细胞中时，肝细胞刺激VLDL的分泌。此外，血清极低密度脂蛋白刺激极低密度脂蛋白，尤其是载脂蛋白B的合成。4.当分泌的极低密度脂蛋白与脂质体或脂蛋白脂酶孵育时，可形成高密度脂蛋白样颗粒。5.组织化学观察到鳗鱼肌肉中脂肪含量较高。门静脉注射~(14)C-极低密度脂蛋白后，~(14)C-极低密度脂蛋白在肌肉、肝脏、心脏和肾脏的掺入率最高。此外，还发现鳗鱼肌肉质膜上存在与极低密度脂蛋白特异结合的蛋白质，其相对分子质量为77,000。

1. Cultured eel-hepatocytes synthesized and secreted the only one kind of lipoprotein, namely VLDL. Although there are two main lipoproteins in eel serum, VLDL and HDL, eel-hepatocytes did not synthesize and secrete HDL. 2. Characterizations of the VLDL. (1) Chemical composition of the VLDL. The contents of rotein, triacylglycerol, free cholesterol, cholesterol ester and phospholipid in the VLDL were 12, 69, 3.6, 0.4 and 14%, respectively. (2) Apoproteins of the VLDL. Main apoproteins of the VLDL were apo A and B. What is most different from VLDLs secreted by mammalian livers is that the secreted VLDLs of mammals do not contain apo A as a main apoprotein. (3) The rate of the VLDL secretion.Cultured eel-hepatocytes secreted the VLDL at the rate of 3.79*1.51mug VLDL/mg cell protein/h(n=6). This value was 10 times higher than the rates of VLDL secretion by human hepatocytes. 3. Effects of insulin and serum lipoproteins. (1) Effect of insulin. Insulin inhibited the secretion of the VLDL and the incorporation of 14C-leucine and 14C-acetate into the VLDL. (2) Effect of serum VLDL. When serum VLDL was added to the eel-hepatocytes, the hepatocytes stimulated the VLDL secretion. Furthermore, the synthesis of apoproteins of the VLDL, especially apo B, was stimulated by the serum VLDL. 4. When the secreted VLDL was incubated with liposomes or lipoprotein lipase, a HDL-like particle was formed. 5. The presence of high content of lipid in eel muscle was histochemically observed. When the incorporation of 14C-VLDL into the muscle, liver, heart and kidney was investigated after the 14C-VLDL was injected into the portal vein, the incorporation into the muscle was the highest. Furthermore, it was found that there was the protein on the plasma membrane of eel muscle which could bind the VLDL specifically and of which molecular weight was 77,000.