The role of the sarcocyst surface apparatus in utilizing the host cell muscle structures

The participation of the sarcocyst surface apparatus (SSA) of two sarcosporidian species, Sarcocystis muris and S. ovifelis (Coccidia, Sporozoa, Apicomplexa), in degradation of disrupted host cell substances was investigated. After degradation, these substances are transported through the membrane of the SSA to the sarcocyst ground substance (GS), but this process cannot be regarded as endocytosis. At first, the transported substances were found in SSA pits in the form of fibrillar structures. Later on, these were seen as twisted up granules. In some cases, such granules restore their fibrillar shape, penetrate through the SSA membrane and appear in the sarcocyst GS. In other cases, the small granules may be released from SSA pits directly to the sarcocyst GS. Besides, two SSA primembrane layers were seen to disappear during the transportation of host cell substances. In addition, multimembrane structures (membranous whorls) were first demonstrated between the plasmalemma and inner membrane complex of the zoite pellicle. Multimembrane structures were found, in addition, in the zoite cytoplasm in connection with micronemes. These structures resembling chloroplast granae of thylakoids may presumably fill the gap in membrane pool of the SSA contributing to its renewal.