title: [The structural and functional analysis of the surface apparatus in four species of Sarcocystis (Sporozoa, Apicomplexa)].
abstract: The comparable ultrastructural analysis of the sarcocyst surface apparatus (SSA) was made for four species of Sarcocystis: Sarcocystis muris, S. fusiformis, S. medusiformis, and Sarcocystis sp. from buffalo heart muscles. In all these species, SSA contains a surface membrane, overmembrane complex with glycocalyx, and submembrane complex made of two glycoprotein SSA primembrane layers. SSA makes numerous primary vesicle-like protrusions and pits in between. Some vesicles containing two layers, PM1 and PM2, are pinching off from the totally formed protrusions. Then these vesicles are directed into infected host cell to participate in its degradation. In the SSA pits neither over-, nor submembrane complex is present, the pits being made of the surface membrane only. It is important that fibrillar structures penetrate through the SSA membrane into pits from the host cell. Besides, SSA forms secondary protrusions with different structures in various species of Sarcocystis. They increase the sarcocyst surface and transport different substances along intermediate filaments from the SSA pits membrane to the sarcocyst body. At the same time, deep invaginations are found in the SSA of old sarcocysts. We thought that these structures increased the sarcocyst surface and thus promote to intensify metabolism. This study-defined presence of membranous vesicles in secondary protrusions. According to their structure and localization, the membranous vesicles may be involved in the building of the sarcocyst surface membrane.
authors.forename: A I
authors.initials: AI
authors.lastname: Radchenko
authors.forename: T V
authors.initials: TV
authors.lastname: Beĭer
mesh_terms: D000818:Animals; D002020:Buffaloes / Q000469:parasitology; D006321:Heart / Q000469:parasitology; D008018:Life Cycle Stages; D012522:Sarcocystis / Q000378:metabolism / Q000648:ultrastructure*