Morgenstern E
Universität des Saarlandes, Homburg/Saar, Fed Rep Germany.
Scanning Microsc Suppl. 1991;5(4):S109-15.
Despite a plethora of reports on the ultrastructure of secretory granule release by exocytosis, the release of coagulant activity from stimulated platelets is still being attributed to membrane vesiculation. Membrane vesiculation and the formation of myelin figures have been shown to be artifacts of glutaraldehyde GA fixation. Cells fixed by direct osmium or rapid freezing are free of such structures. Yet there is still doubt that rapid freezing interferes with vesiculation process. This study has addressed this issue by examining: (1) whether freezing and freeze-substitution affects membrane vesiculation, (2) whether paraformaldehyde-fixation also induces the phenomenon, and (3) whether the aldehyde concentration is of influence. Aldehyde fixation was carried out prior to impact freezing and freeze-substitution. In thrombin-stimulated platelets, membrane vesiculation and myelin figures were found. Glutaraldehyde induced multivesicular structures, paraformaldehyde or low aldehyde concentrations only blebs on the platelet surface. The membrane vesicles were in continuity with the cytoplasmic matrix. Unstimulated platelets did not show vesiculation or myelin figures. Control samples, without aldehyde fixation, showed instead of membrane vesiculation, granule fusion with the plasmalemma, or, instead of myelin figures, compound granules. This confirms that membrane vesiculation and the formation of myelin figures are artifacts induced by the failure of aldehydes to arrest lipid mobility within membranes undergoing rapid changes in structure. Although the presence of membrane vesiculation and myelin figures in platelets indicates that exocytotic processes were occurring at the moment of aldehyde fixation, the finding of membrane vesiculation in aldehyde-fixed platelets does not indicate a separate type of exocytosis.
尽管关于通过胞吐作用释放分泌颗粒的超微结构已有大量报道，但刺激血小板释放凝血活性仍被归因于膜泡形成。膜泡形成和髓鞘样结构的形成已被证明是戊二醛（GA）固定的人为产物。用直接锇固定或快速冷冻固定的细胞没有这种结构。然而，人们仍然怀疑快速冷冻是否会干扰膜泡形成过程。本研究通过研究以下方面解决了这个问题：（1）冷冻和冷冻置换是否影响膜泡形成，（2）多聚甲醛固定是否也会诱导这种现象，以及（3）醛浓度是否有影响。在冲击冷冻和冷冻置换之前进行醛固定。在凝血酶刺激的血小板中，发现了膜泡形成和髓鞘样结构。戊二醛诱导形成多囊泡结构，多聚甲醛或低醛浓度仅诱导血小板表面出现泡状突起。膜泡与细胞质基质连续。未刺激的血小板未显示膜泡形成或髓鞘样结构。未进行醛固定的对照样品显示，没有膜泡形成，而是颗粒与质膜融合，或者没有髓鞘样结构，而是复合颗粒。这证实了膜泡形成和髓鞘样结构的形成是醛未能阻止结构快速变化的膜内脂质流动性而诱导的人为产物。尽管血小板中膜泡形成和髓鞘样结构的存在表明在醛固定时正在发生胞吐过程，但在醛固定的血小板中发现膜泡形成并不表明存在一种单独的胞吐类型。
