THE PI EFFECT AND PLATELET ALPHA-ADRENERGIC STIMULATION

磷脂酰肌醇（PI）的水解反应是一个复杂的过程， 在一种机制中的门控功能， 细胞表面诱导Ca++的移动。 人类的血小板 显示含有PI-特异性磷脂酶C（PI-PLC）， 通过将血小板暴露于凝血酶。 它们还含有α-肾上腺素能 受体，其在刺激时导致Ca++跨血浆转运 膜，增强PI的合成，并抑制腺苷酸环化酶 活动 我们建议确定1）是否水解 磷酸肌醇发生在肾上腺素激活的血小板中， 各种条件，以及PI控制的情况 这种血小板中的代谢与PI的Ca++门控作用一致 周转，2）胆固醇富集/消耗或治疗的影响 与PI-PLC对血小板膜腺苷酸环化酶活性的影响，3） 血小板中是否存在多磷酸肌醇特异性PLC 膜，4）其他磷脂和脂肪酸的影响， 可溶性PI-PLC的活性，以及5）通过 肾上腺素或胶原的腺苷酸环化酶抑制剂SQ 22536，ADP， 和低剂量凝血酶诱导的血小板磷脂水解。 为 在大多数这些研究中，我们将采用脂质分离技术， 我们所熟悉的包括TLC、HPLC和GC。 普莱森特将是 使用富含或缺乏胆固醇的 磷脂囊泡及其膜分离的方法现在使用 常规地在这个实验室中，这产生了腺苷酸 环化酶对肾上腺素和PGD 2有反应。 PI的营业额将为 借助放射性同位素标记和质量 决心。 阐明α-肾上腺素能神经元的作用 刺激，特别是作为其他激动剂的协同队列以及作为 这一事件已经被证明特别容易受到修改， 胆固醇，应该加强我们对控制事件的理解。 正常和病理状态如血栓形成中的血小板聚集。

It has been suggested that the hydrolysis of phosphatidylinositol (PI) has a gating function in a mechanism whereby the activation of receptors at cell surfaces induces the mobilization of Ca++. Human platelets have been shown to contain a PI-specific phospholipase C (PI-PLC) which is activated by exposure of platelets to thrombin. They also contain Alpha-adrenergic receptors which, upon stimulation, lead to Ca++ transport across the plasma membrane, enhanced synthesis of PI, and depressed adenylate cyclase activity. We propose to determine 1) whether hydrolysis of phosphoinositides occurs in platelets activated by epinephrine under a variety of conditions, and whether the circumstances controlling PI metabolism in such platelets are consistent with a Ca++-gating role for PI turnover, 2) the effects of cholesterol enrichment/depletion or treatment with PI-PLC upon the activity of platelet membrane adenylate cyclase, 3) whether a polyphosphoinositide-specific PLC is present in platelet membranes, 4) the effects of other phospholipids and fatty acid on the activity of soluble PI-PLC, and 5) the extent of potentiation by epinephrine or the adenylate cyclase inhibitor SQ22536 of collagen, ADP, and low-dose thrombin-induced hydrolysis of platelet phospholipid. For most of these studies, we will employ techniques of lipid resolution with which we are familiar, including TLC, HPLC, and GC. Platelets will be loaded with or depleted of cholesterol using cholesterol-rich or -poor phospholipid vesicles, and their membranes isolated by a method now used routinely in this laboratory, which yields preparations whose adenylate cyclase is responsive to epinephrine and PGD2. Turnover of PI will be assessed with the aid of both radioisotopic labeling and mass determinations. The clarification of the role of Alpha-adrenergic stimulation, particularly as a synergistic cohort for other agonists and as an event already shown to be especially susceptible to modification by cholesterol, should enhance our understanding of the events controlling platelet aggregation in normal and pathological states such as thrombosis.