Soslau G, Schechner A J, Alcasid P J, Class R
Department of Biochemistry, MCP Hahnemann School of Medicine, Philadelphia, Pennsylvania 19102-1192, USA.
Thromb Res. 2000 Jan 15;97(2):15-27. doi: 10.1016/s0049-3848(99)00124-3.
Platelets are subjected to vastly differing shear forces under laminar and nonlaminar flow patterns throughout the tortuous cardiovascular system. Different activation pathways appear to be associated with platelet adhesion and aggregation under high shear rates vs. low shear rates. We found that platelets continue to aggregate at very low stirring rates (100 RPM) and low shear forces although significantly less than at high stirring rates (1000 RPM). These conditions may model vortices encountered in vivo, such as downstream of partially occluded blood vessels. The extent of agonist-induced platelet aggregation, at varying stir rates, remained essentially unchanged between 1200 and 600 RPM. This was true for both freshly prepared and stored platelets even though the extent of aggregation was significantly reduced with stored platelets. Agonists used were thrombin, thrombin receptor activating peptide (TRAP), SFLLRNP, the thromboxane A2 mimetic, U46619, plus epinephrine and ADP+epinephrine. At lower stir rates (100-400 RPM), little or no difference in aggregation levels was observed between fresh and stored platelets, depending upon agonist used. This may indicate that old and young platelets, in vivo, would be equally active at vessel walls exposed to blood flowing through a slow vortex at low shear rates. ATP, released from activated platelets, may act as a potent regulator of platelet aggregation within a vortex where the resident time of platelets and bioactive molecules is greater than in laminar flow regions. High levels of extracellular ATP (100 microM) inhibited agonist-induced aggregation of fresh platelets to a greater extent than stored platelets, except with ADP+epinephrine where the converse was observed. Inhibition, in general, appeared to be inversely related to stir rates. Low levels of extracellular ATP (10 nM, 1 microM) generally stimulated agonist-induced aggregations independent of stir rates and to a greater extent with stored platelets than fresh platelets. Unraveling how hemostasis functions within microenvironments may facilitate ways to further regulate this process.
在整个曲折的心血管系统中，血小板在层流和非层流模式下会受到截然不同的剪切力。在高剪切速率与低剪切速率下，不同的激活途径似乎与血小板的黏附和聚集有关。我们发现，血小板在非常低的搅拌速率（100转/分钟）和低剪切力下仍会继续聚集，尽管明显少于在高搅拌速率（1000转/分钟）下的聚集。这些条件可能模拟了体内遇到的涡流，例如部分阻塞血管的下游。在1200至600转/分钟之间，不同搅拌速率下激动剂诱导的血小板聚集程度基本保持不变。对于新鲜制备的血小板和储存的血小板都是如此，尽管储存血小板的聚集程度明显降低。使用的激动剂有凝血酶、凝血酶受体激活肽（TRAP）、SFLLRNP、血栓素A2模拟物U46619，以及肾上腺素和ADP + 肾上腺素。在较低的搅拌速率（100 - 400转/分钟）下，新鲜血小板和储存血小板之间的聚集水平几乎没有差异，这取决于所使用的激动剂。这可能表明，在体内，老年和年轻血小板在暴露于低剪切速率下缓慢涡流中的血管壁处具有同等活性。从活化血小板释放的ATP可能作为血小板在涡流中聚集的有效调节剂，在涡流中血小板和生物活性分子的停留时间比在层流区域更长。高浓度的细胞外ATP（100微摩尔）比储存血小板更能抑制新鲜血小板的激动剂诱导聚集，但ADP + 肾上腺素的情况则相反。一般来说，抑制作用似乎与搅拌速率呈负相关。低浓度的细胞外ATP（10纳摩尔、1微摩尔）通常会刺激激动剂诱导的聚集，且与搅拌速率无关，并且储存血小板比新鲜血小板的刺激程度更大。弄清楚止血在微环境中的作用机制可能有助于找到进一步调节这一过程的方法。
