Endocytosis in Trypanosoma cruzi is mainly performed through a specialised membrane domain called cytostome-cytopharynx complex. Its ultrastructure and dynamics in endocytosis are well characterized in epimastigotes, being absent in trypomastigotes, that lack endocytic activity. Intracellular amastigotes also possess a cytostome-cytopharynx but participation in endocytosis of these forms is not clear. Extracellular amastigotes can be obtained from the supernatant of infected cells or in vitro amastigogenesis. These amastigotes share biochemical and morphological features with intracellular amastigotes but retain trypomastigote's ability to establish infection. We analysed and compared the ultrastructure of the cytostome-cytopharynx complex of intracellular amastigotes and extracellular amastigotes using high-resolution tridimensional electron microscopy techniques. We compared the endocytic ability of intracellular amastigotes, obtained through host cell lysis, with that of extracellular amastigotes. Intracellular amastigotes showed a cytostome-cytopharynx complex similar to epimastigotes'. However, after isolation, the complex undergoes ultrastructural modifications that progressively took to an impairment of endocytosis. Extracellular amastigotes do not possess a cytostome-cytopharynx complex nor the ability to endocytose. Those observations highlight morpho functional differences between intra and extracellular amastigotes regarding an important structure related to cell metabolism.

中文翻译：

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克氏锥虫细胞内和细胞外无鞭毛体的细胞口-细胞咽复合体表现出结构和功能差异

克氏锥虫的内吞作用主要通过称为细胞口-细胞咽复合物的特殊膜结构域进行。其内吞作用的超微结构和动力学在上鞭毛体中得到很好的表征，在缺乏内吞活性的锥体鞭毛体中不存在。细胞内无鞭毛体也具有细胞口 - 细胞咽，但参与这些形式的内吞作用尚不清楚。细胞外无鞭毛体可以从感染细胞的上清液或体外无鞭毛发生中获得。这些无鞭毛体与细胞内无鞭毛体具有共同的生化和形态特征，但保留了锥体鞭毛体建立感染的能力。我们使用高分辨率三维电子显微镜技术分析和比较了细胞内无鞭毛体和细胞外无鞭毛体的细胞口-细胞咽复合物的超微结构。我们比较了通过宿主细胞裂解获得的胞内无鞭毛体与胞外无鞭毛体的内吞能力。细胞内的无鞭毛体表现出与上鞭毛体相似的细胞口-细胞咽复合体。然而，在分离后，复合物经历了超微结构修饰，逐渐导致内吞作用受损。细胞外无鞭毛体不具有细胞口-细胞咽复合体，也不具有内吞能力。这些观察结果突出了细胞内和细胞外无鞭毛体之间关于与细胞代谢相关的重要结构的形态功能差异。然而，在分离后，复合物经历了超微结构修饰，逐渐导致内吞作用受损。细胞外无鞭毛体不具有细胞口-细胞咽复合体，也不具有内吞能力。这些观察结果突出了细胞内和细胞外无鞭毛体之间关于与细胞代谢相关的重要结构的形态功能差异。然而，在分离后，复合物经历了超微结构修饰，逐渐导致内吞作用受损。细胞外无鞭毛体不具有细胞口-细胞咽复合体，也不具有内吞能力。这些观察结果突出了细胞内和细胞外无鞭毛体之间关于与细胞代谢相关的重要结构的形态功能差异。