通过改变细胞内钙水平和蛋白激酶C的活性来改变大鼠肝细胞极低密度脂蛋白的分泌。

Varying very low-density lipoprotein secretion of rat hepatocytes by altering cellular levels of calcium and the activity of protein kinase C.

作者信息

Björnsson O G, Bourgeois C S, Gibbons G F

机构信息

Metabolic Research Laboratory University of Oxford, Radcliff Infirmary, U.K.

出版信息

Eur J Clin Invest. 1998 Sep;28(9):720-9. doi: 10.1046/j.1365-2362.1998.00354.x.

DOI:10.1046/j.1365-2362.1998.00354.x

PMID:9767371

Abstract

BACKGROUND

Calcium antagonists lower plasma levels of lipoproteins and suppress hepatic very low-density lipoprotein (VLDL) secretion. Similar effects have been observed with the calcium ionophore A23187. We studied further the effect of calcium on VLDL metabolism.

METHODS

Hepatocytes from male Wistar rats were isolated and cultured in the presence or absence of calcium-mobilizing hormones, or compounds that either stimulate or inhibit the activity of protein kinase C. Secreted VLDL (d < 1.006 g mL-1) was isolated by centrifugation (145,000 x g), and lipids and apolipoprotein B were analysed.

RESULTS

VLDL secretion reached maximum in hepatocytes cultured in medium containing calcium 0.8-2.4 mmolL-1. Depleting the cells of calcium by incubating in calcium-free medium or by treating the cells with the Ca(2+)-ATPase inhibitor thapsigargin (5 x 10-7 molL-1) suppressed lipid secretion to less than 15% of control, and this was accompanied by an increase in cellular levels of triacylglycerol. Calcium loading (medium calcium > 2.4 mmolL-1) suppressed both lipoprotein secretion and cellular levels of lipids, suggesting a reduced overall rate of lipid synthesis. At an extracellular calcium concentration of 0.8 mmolL-1, angiotensin II, vasopressin, endothelin-1 (10(-7) molL-1) or phenylephrine (10(-4) molL-1) suppressed VLDL secretion (maximum to 37% of control), and elevated medium calcium attenuated this effect. The protein kinase C inhibitor chelerythrine (5 x 10(-5) molL-1) and the protein kinase C activator phorbol 12-myristate 13-acetate (PMA) (10(-6) molL-1), suppressed VLDL secretion to 18% and 60% of control, respectively, whereas the protein kinase C-inactive 4 alpha-PMA was without an effect. No effect on ketogenesis was observed by these compounds, indicating that suppressed lipid secretion was not due to an enhanced oxidation of lipids.

CONCLUSIONS

Hepatic VLDL secretion can be related to changes in hepatocyte levels of calcium and the activity of protein kinase C.

摘要

背景

钙拮抗剂可降低血浆脂蛋白水平并抑制肝脏极低密度脂蛋白（VLDL）的分泌。钙离子载体A23187也有类似作用。我们进一步研究了钙对VLDL代谢的影响。

方法

分离雄性Wistar大鼠的肝细胞，在有无钙动员激素或刺激或抑制蛋白激酶C活性的化合物存在的情况下进行培养。通过离心（145,000×g）分离分泌的VLDL（d<1.006 g/mL），并分析脂质和载脂蛋白B。

结果

在含钙0.8 - 2.4 mmol/L的培养基中培养的肝细胞中，VLDL分泌达到最大值。通过在无钙培养基中孵育或用Ca(2+) - ATP酶抑制剂毒胡萝卜素（5×10 - 7 mol/L）处理细胞来耗尽细胞内的钙，可将脂质分泌抑制至对照的15%以下，同时细胞内三酰甘油水平升高。钙负荷（培养基钙>2.4 mmol/L）抑制脂蛋白分泌和细胞内脂质水平，表明脂质合成的总体速率降低。在细胞外钙浓度为0.8 mmol/L时，血管紧张素II、血管加压素、内皮素-1（10(-7) mol/L）或去氧肾上腺素（10(-4) mol/L）抑制VLDL分泌（最大抑制至对照的37%），而培养基钙升高可减弱这种作用。蛋白激酶C抑制剂白屈菜红碱（5×10(-5) mol/L）和蛋白激酶C激活剂佛波酯12 - 肉豆蔻酸13 - 乙酸酯（PMA）（10(-6) mol/L）分别将VLDL分泌抑制至对照的18%和60%，而无蛋白激酶C活性的4α - PMA则无作用。这些化合物对生酮作用无影响，表明脂质分泌受抑制并非由于脂质氧化增强。