Pittner R A, Fears R, Brindley D N
Biochem J. 1985 Sep 1;230(2):525-34. doi: 10.1042/bj2300525.
Rat hepatocytes were incubated in monolayer culture for 8 h. Glucagon (10nM) increased the total phosphatidate phosphohydrolase activity by 1.7-fold. This effect was abolished by adding cycloheximide, actinomycin D or 500 pM-insulin to the incubations. The glucagon-induced increase was synergistic with that produced by an optimum concentration of 100 nM-dexamethasone. Theophylline (1mM) potentiated the effect of glucagon, but it did not affect the dexamethasone-induced increase in the phosphohydrolase activity. The relative proportion of the phosphohydrolase activity associated with membranes was decreased by glucagon when 0.15 mM-oleate was added 15 min before the end of the incubations to translocate the phosphohydrolase from the cytosol. This glucagon effect was not seen at 0.5 mM-oleate. Since glucagon also increased the total phosphohydrolase activity, the membrane-associated activity was maintained at 0.15 mM-oleate and was increased at 0.5 mM-oleate. This activity at both oleate concentrations was also increased in incubations that contained dexamethasone, particularly in the presence of glucagon. Insulin increased the relative proportion of phosphatidate phosphohydrolase that was associated with membranes at 0.15 mM-oleate, but not at 0.5 mM-oleate. It also decreased the absolute phosphohydrolase activity on the membranes at both oleate concentrations in incubations that also contained glucagon and dexamethasone. None of the hormonal combinations significantly altered the total glycerol phosphate acyltransferase activity. However, glucagon significantly increased the microsomal activities, and insulin had the opposite effect. Glucagon also decreased the mitochondrial acyltransferase activity. There was a highly significant correlation between the total phosphatidate phosphohydrolase activity and the synthesis of neutral lipids from glycerol phosphate and 0.5 mM-oleate in homogenates of cells from all of the hormonal combinations. Phosphatidate phosphohydrolase activity is increased in the long term by glucocorticoids and also by glucagon through cyclic AMP. In the short term, glucagon increases the concentration of fatty acid required to translocate the cytosolic reservoir of activity to the membranes on which phosphatidate is synthesized. Insulin opposes the combined actions of glucagon and glucocorticoids. The long-term events explain the large increases in the phosphohydrolase activity that occur in vivo in a variety of stress conditions. The expression of this activity depends on increases in the net availability of fatty acids and their CoA esters in the liver.
将大鼠肝细胞进行单层培养8小时。胰高血糖素（10nM）可使总磷脂酸磷酸水解酶活性提高1.7倍。在培养物中添加放线菌酮、放线菌素D或500pM胰岛素可消除这种作用。胰高血糖素诱导的增加与最佳浓度100nM地塞米松产生的增加具有协同作用。茶碱（1mM）增强了胰高血糖素的作用，但不影响地塞米松诱导的磷酸水解酶活性增加。当在培养结束前15分钟添加0.15mM油酸以将磷酸水解酶从胞质溶胶转运出来时，胰高血糖素会降低与膜相关的磷酸水解酶活性的相对比例。在0.5mM油酸时未观察到这种胰高血糖素效应。由于胰高血糖素也增加了总磷酸水解酶活性，因此在0.15mM油酸时膜相关活性得以维持，而在0.5mM油酸时则增加。在含有地塞米松的培养物中，尤其是在有胰高血糖素存在的情况下，这两种油酸浓度下的这种活性也会增加。胰岛素增加了在0.15mM油酸时与膜相关的磷脂酸磷酸水解酶的相对比例，但在0.5mM油酸时未增加。在同时含有胰高血糖素和地塞米松的培养物中，胰岛素还降低了两种油酸浓度下膜上的磷酸水解酶绝对活性。没有一种激素组合能显著改变总甘油磷酸酰基转移酶活性。然而，胰高血糖素显著增加了微粒体活性，而胰岛素则有相反的作用。胰高血糖素还降低了线粒体酰基转移酶活性。在所有激素组合的细胞匀浆中，总磷脂酸磷酸水解酶活性与由甘油磷酸和0.5mM油酸合成中性脂质之间存在高度显著的相关性。长期来看，糖皮质激素和胰高血糖素通过环磷酸腺苷增加磷脂酸磷酸水解酶活性。短期内，胰高血糖素增加了将胞质溶胶中活性储备转运至合成磷脂酸的膜上所需的脂肪酸浓度。胰岛素对抗胰高血糖素和糖皮质激素的联合作用。长期事件解释了在各种应激条件下体内磷脂酸磷酸水解酶活性的大幅增加。这种活性的表达取决于肝脏中脂肪酸及其辅酶A酯净可用性的增加。
