• 作者： Holm Holmsen
• 作者服務機構： 挪威伯根大學生化學系
• 中文摘要： 血小板胞膜具有各種精緻的受器，當受器銜接上其特異的生理活化物或外在的表面物質，血小板就依序發生：
  細胞型態變化；凝聚；分泌出細胞內含物；和釋放花生烯四酸。
  血小板分泌出的內含物有三種不同的來源：1）由濃密顆粒體放出的腺?二磷酸和血清促進素；2）由阿爾發顆粒體
  放出的凝血因子，血小板特異蛋白和黏著蛋白；3）由溶小體放出的酸性水解?。釋放出的花生烯四酸則在血小板內
  被代謝成前列腺素和前列凝素。這兩類代謝物和血小板釋出的腺?二磷酸，以及血小板細胞間的接觸，共同引起正
  回饋作用而活化血小板。有些活化性弱的刺激劑如腺?二磷酸，後葉加壓素和血小板活化因子就須靠正回饋作用來
  推展血小板的全程反應。而活化性強的刺激物，如凝血?和生膠質，則不須經由正回饋作用就能刺激血小板的全程
  反應。
  大部份的活化劑所刺激血小板凝聚是經由被活化的G蛋白，來活化磷脂?丙，此?水解磷脂肌醇-4,5-二磷酸，
  產生肌醇-1,4,5-三磷酸和甘油二酯，前者會移動胞內鈣離子，後者會活化蛋白激?丙。細胞內鈣離子的增加會導致
  某些蛋白的磷酸化，而引發血小板凝聚反應的進行。而蛋白激?丙的被活化則影響鈉／氫交換蛋白，而改變細胞內
  酸鹼度，並中止鈣離子調理的信息傳遞。另外的刺激物如前列腺素I2和D2則經由活化腺環?而抑制血小板的被活
  化。
  e
• 英文摘要： Platelets respond through diserete receptors to a number of physiological stimuli and foreign surfaceswith a sequence of measurable responses: shape change, aggregation, secretion and arachidonate liberation.Three secretory responses are distinguished: release of substances from 1) dense granules (ADP, serotonin),2) α-granules (coagulation factors, platelet-specific proteins, adhesive proteins) and 3) lysosomes (acidhydrolases). The liberated araehidonate is converted to prostaglandins and thromboxanes which, togetherwith secreted ADP and close cell contact, will cause further platelet activation through“positive feedback”(autocrine stimulation). Some agonists are“weak”(ADP, vasopressin, platelet-activating factor) anddepend on positive feedback to promote the full sequence of responses, while other agonists“strong”(thrombin, collagen) and stimulate the entire response sequence without positive feedback. Most agonistsappear to stimulate platelet responses G-protein-dependent activation of phospholipase C, resulting indiesteratic hydrolysis of phosphatidylinositol-4,5-bisphosphate yielding inositol-1,4,5-trisphosphate anddiacylglycerol. There are signal molecules which mobilize cytoplasmic Ca and stimulate protein kinaseC, respectively. cytoplasmic Ca will in turn activate protein phosphorylations which eventually lead to execution of the various responses while activation of protein kinase C appears to be linked to regulation of intracellular pH through exchanger and to termination of the Ca -mediated signal processing.Other agonists (prostaglzndins I2 and D2)counteract platelet stimulation through classical activation of adenylate cyclase.
• 中文關鍵字： platelet secretion; polyphosphoinositides; dense granule; α-granule; acid hydrolases; adenylate cyclase; diacylglycerol; inositol phosphates.
• 英文關鍵字： --