Roles of Phospholipid Molecular Species in Cell Signaling

研究了磷脂分子在细胞信号转导中的作用。用凝血酶和胶原蛋白刺激人血小板，测定不同分子种类磷脂的质量变化。在刺激下，磷脂酰肌醇和磷脂酰丝氨酸的每个分子物种都被同等地水解，而含有花生四烯酸的磷脂酰胆碱和二酰基和烯基磷脂酰乙醇嗪的分子物种被选择性地水解。血栓素A_2拮抗剂ONO3708可完全抑制胶原激活过程中人血小板胞浆内游离钙的增加。半最大钙释放和钙内流分别需要3和4 nM的STA_2，一个稳定的血栓素A_2模拟物。然而，磷脂酶C的半最大激活需要大约18 nM的STA_2。钙通道阻滞剂…硝苯地平是一种二氢吡啶衍生物，可抑制胶原或低浓度STA_2(10 NM)引起的内库钙内流和释放，但不能抑制凝血酶或高浓度STA_2(100 NM)引起的内库钙内流和钙释放。这些结果表明，中国仓鼠V79-UF细胞存在两种不同的、对二氢吡啶敏感和不敏感的钙通道，这两种通道依赖于人血小板中激动剂的浓度和种类。中国仓鼠V79-UF细胞在37ﾟC孵育8分钟后，通过Percoll密度梯度和蔗糖密度梯度的等量离心，将标记的表皮生长因子掺入中国仓鼠V79-UF细胞内，并使其高度浓缩。在磷脂组成方面，内吞体膜与质膜不同。含有两种单烯脂肪酸的二酰基磷脂酰乙醇胺和二酰基磷脂酰乙醇胺的分子种类在内体中的含量低于质膜。无论质膜中磷脂分子种类的比例是否发生变化，内体和质膜中磷脂的极性头基和分子种类组成的差异都不会改变。较少

Roles of phospholipid molecular species in cell signaling were studied. Mass changes in the various molecular species of phospholipids were determined after stimulation of human platelets with thrombin and collagen. Upon stimulation, every molecular species of phosphatidylinositol and phosphatidylserine was equally hydrolyzed, whereas the molecular species of phosphatidylcholine and diacyl- and alkenylacyl-phosphatidylethanolazine containing arachidonic acid were selectively hydrolyzed. The Ca^<2+> concentration affects the differential degradation of phospholipid molecular species in activated human platelets.The thromboxane A_2 antagonist, ONO3708, completely inhibited the increase in cytosolic free Ca^<2+> in human platelets during activation with collagen. Half-maximal Ca^<2+> release and influx required about 3 and 4 nM STA_2, a stable thromboxane A_2 mimetic, respectively. However, half-maximal activation of phospholipase C required about 18 nM STA_2.The Ca^<2+> channel blocker, … More nifedipine, a dihydropyridine derivative, inhibited the Ca^<2+> influx and release from internal stores caused by collagen or a low concentration of STA_2 (10 nM), but did not inhibit those caused by thrombin or a high concentration of STA_2 (100 nM). These results indicate the presence of two distinct, dihydropyridine-sensitive and insensitive, Ca^<2+> channels dependent on the concentrations and classes of agonists in human platelets.^<125>I-labeled epidermal growth factor was incorporated into and highly concentrated in endosomes of Chinese hamster V79-UF cells during incubation at 37ﾟC for 8 min after binding to its receptors on the cell surface at 4ﾟC. From the labeled cells, endosomes were isolated by isopyenic centrifugation on a Percoll density gradient and then sucrose density gradients. Endosome membranes were found to differ from plasma membranes in the phospholipid composition. The contents of molecular species of diacylphosphatidyleholine and diacylphosphatidylethanolamine with two monoenoic fatty acids were lower in endosomes than in plasma membranes. The differences in the polar head group and molecular species compositions of phospholipids between endosomes and plasma membranes did not change, regardless of whether or not the proportions of phospholipid molecular species in plasma membranes changed. Less