Davies T A, Drotts D, Weil G J, Simons E R
Department of Biochemistry, Boston University School of Medicine, Massachusetts 02118.
Cytometry. 1988 Mar;9(2):138-42. doi: 10.1002/cyto.990090207.
Thrombin-induced stimulation of human platelets is accompanied by a dramatic increase in cytoplasmic calcium concentrations followed by a slow decrease. These changes are very rapid, are maximal by 10-15 s, and can be detected with probes such as Indo-1. Suspension studies using spectrofluorometry, which reflect a value which is the average of 3 x 10(7) cells per ml, indicate a thrombin dose-dependent increase in cytoplasmic calcium at doses up to 0.025 units per ml. We show here, using flow cytometry, that at less than half-saturating thrombin doses only subpopulations of platelets rather than the entire sample are responding. The extent of these responses, however, still depends on thrombin concentration. When the thrombin doses are between half and fully saturating, one subpopulation responds fully (i.e., its extent of increase in cytoplasmic calcium concentration, [Ca++]in is 100% of that seen at saturating thrombin concentrations) while the remaining platelets respond partially or not at all. There is thus evidence of positive cooperativity leading to disproportionate thrombin receptor occupancy on different subpopulations when platelets are subjected to subsaturating doses of thrombin. The existence of responding subpopulations may explain how the reported multiple stimulations of the same suspension of platelets at low thrombin doses occur.
凝血酶诱导的人血小板刺激伴随着细胞质钙浓度的急剧增加，随后缓慢下降。这些变化非常迅速，在10 - 15秒时达到最大值，并且可以用诸如Indo - 1等探针检测到。使用荧光分光光度法进行的悬浮研究反映的是每毫升3×10⁷个细胞的平均值，结果表明在每毫升高达0.025单位的剂量下，细胞质钙的增加呈凝血酶剂量依赖性。我们在此使用流式细胞术表明，在低于半饱和凝血酶剂量时，只有血小板亚群而非整个样本有反应。然而，这些反应的程度仍取决于凝血酶浓度。当凝血酶剂量处于半饱和至完全饱和之间时，一个亚群会完全反应（即其细胞质钙浓度[Ca²⁺]in的增加程度是在饱和凝血酶浓度下观察到的100%），而其余血小板则部分反应或根本不反应。因此，有证据表明存在正协同作用，当血小板受到低于饱和剂量的凝血酶作用时，会导致不同亚群上凝血酶受体占据比例不均衡。反应性亚群的存在可能解释了在低凝血酶剂量下同一血小板悬浮液所报告的多次刺激是如何发生的。
