Smith C M, Burris S M, White J G
Department of Pediatrics, University of Minnesota Health Science Center, Minneapolis.
Blood. 1989 May 1;73(6):1570-5.
Platelet release has been alternatively viewed as a fragmentation of platelet territories demarcated within the cytoplasm of mature megakaryocytes or as a later event involving segmentation of proplatelet pseudopodia extended from the cell. The mechanical constraints on platelet release were evaluated by measuring the resistance of guinea pig megakaryocytes to aspiration into micropipettes of similar diameter to the width of naturally forming proplatelet projections. Application of increasing negative pressure to the surface of the cells resulted in progressively longer extensions being drawn into the pipette until maximal extension lengths were reached. None of the passively aspirated cytoplasmic extensions fragmented off the cells even at the highest aspiration pressure under physiologic study conditions. The longest extensions were aspirated from megakaryocytes of the most advanced maturation stage, and a proportion of the mature cells yielded very long extensions over 50 mu and up to 150 mu in length. Surprisingly, the ease of aspiration did not correlate to cell size during any stage of maturation. The mechanical behavior of guinea pig megakaryocytes indicates a large availability of surface for extension in mature cells ideal for active proplatelet projection. The lack of mechanical fragility suggests that platelet release is a very late maturational event not yet initiated in the "mature" megakaryocytes available for study from marrow harvests.
血小板释放可被另一种观点认为是成熟巨核细胞胞质内划定的血小板区域的碎片化，或者是涉及从细胞延伸出的前血小板伪足分段的后期事件。通过测量豚鼠巨核细胞对吸入与自然形成的前血小板突起宽度相似直径的微量移液器的阻力，评估血小板释放的机械限制。对细胞表面施加逐渐增加的负压会导致越来越长的延伸部分被吸入移液器，直到达到最大延伸长度。即使在生理研究条件下的最高吸入压力下，被动吸入的细胞质延伸部分也没有从细胞上断裂下来。最长的延伸部分是从最成熟阶段的巨核细胞中吸出的，并且一部分成熟细胞产生了非常长的延伸部分，长度超过50微米，最长可达150微米。令人惊讶的是，在任何成熟阶段，吸入的难易程度与细胞大小均无关联。豚鼠巨核细胞的机械行为表明，成熟细胞中存在大量可用于延伸的表面，这对于活跃的前血小板突起是理想的。缺乏机械脆性表明血小板释放是一个非常晚期的成熟事件，在从骨髓收获中获得的可用于研究的“成熟”巨核细胞中尚未启动。
