Packham M A, Bryant N L, Guccione M A, Kinlough-Rathbone R L, Mustard J F
Department of Biochemistry, University of Toronto, Ontario, Canada.
Thromb Haemost. 1989 Nov 24;62(3):968-76.
The effect of the concentration of Ca2+ in the suspending medium of human and rabbit platelets on aggregation, release of 14C-serotonin, and TXB2 formation in response to ADP, thrombin, 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (PAF), collagen and arachidonic acid was studied in either platelet-rich plasma anticoagulated with D-phenylalanyl-prolyl-arginyl chloromethylketone (PPACK) or citrate, or suspensions of washed platelets in modified Tyrode-albumin solutions containing 1 mM Mg2+ and concentrations of added Ca2+ ranging from 0 to 5 mM. In response to ADP, thrombin, or PAF, human platelets were stimulated to form TXA2 by close platelet contact in a low-Ca2+ medium; at physiological concentrations of Ca2+, TXB2 formation was much less and declined progressively as the concentration of Ca2+ was raised. When the formation of TXA2 was blocked with aspirin or indomethacin, aggregation and release by human platelets were strongest at physiological concentrations of Ca2+. Rabbit platelet responses differed markedly from those of human platelets because close contact of rabbit platelets in a low-Ca2+ medium did not promote TXA2 formation. Rabbit platelet responses were more strongly inhibited by the lack of added Ca2+ in the medium than the responses of human platelets, possibly because rabbit platelets do not contain releasable Ca2+. In all studies of human platelets in media with low concentrations of Ca2+, the additional contribution to platelet responses of TXA2 formed because of close platelet contact should be considered because TXA2 formation is not usually stimulated in this way at physiological concentrations of Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)
在富含血小板血浆中，用D - 苯丙氨酰 - 脯氨酰 - 精氨酰氯甲基酮（PPACK）或柠檬酸盐抗凝，或者在含有1 mM镁离子且添加钙离子浓度范围为0至5 mM的改良台氏白蛋白溶液中制备洗涤血小板悬液，研究了人及兔血小板悬浮介质中钙离子浓度对血小板聚集、14C - 5羟色胺释放以及对ADP、凝血酶、1 - O - 烷基 - 2 - 乙酰 - sn - 甘油 - 3 - 磷酸胆碱（PAF）、胶原和花生四烯酸反应时TXB2形成的影响。在低钙离子介质中，通过紧密的血小板接触，人血小板对ADP、凝血酶或PAF刺激形成血栓素A2（TXA2）；在生理浓度的钙离子下，TXB2形成少得多，且随着钙离子浓度升高而逐渐下降至最低。当用阿司匹林或吲哚美辛阻断TXA2形成时，人血小板在生理浓度的钙离子下聚集和释放最强。兔血小板反应与人血小板明显不同，因为在低钙离子介质中兔血小板紧密接触并不促进TXA2形成。与人类血小板相比，介质中缺乏添加的钙离子对兔血小板反应的抑制作用更强，可能是因为兔血小板不含可释放的钙离子。在所有低钙离子浓度介质中对人血小板的研究中，应考虑因紧密血小板接触而形成的TXA2对血小板反应的额外贡献，因为在生理浓度的钙离子下通常不会以这种方式刺激TXA2形成。（摘要截短于250字）
