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The contractile vacuole

Studies carried out with several protozoa, especially free-living ones, have shown that the contractile vacuole plays a fundamental role in the regulation of osmotic processes. There have been few reports on the presence of such a structure in trypanosomes. The structure was reported to consist of several tubules connected to a central vacuole located close to the flagellar pocket.24 Aquaporin, a protein involved in water transport, was identified in T. cruzi epimastigotes and localized to both the acidocalcisomes and contractile vacuole.25 It was shown that the fusion of acidocalcisomes to the contractile vacuole takes place in a process mediated by cyclic AMP.26 Recently, the contractile vacuole has been shown to be important for the regulatory volume decrease that occurs after hypoosmotic stress27 and for cell shrinking after hyperosmotic stress.21 In addition, the contractile vacuole is also involved in the trafficking of glycosylphosphatidylinositol (GPI)-anchored proteins to the plasma membrane.28 Proteomic, bioinformatic, and ultrastructural analyses demonstrated that a number of proteins are involved in trafficking, such as SNARE 2.1 and SNARE 2.2, VAMP1 (an orthologue of mammalian VAMP7), AP180, and the small GTPases Rab11 and Rab32.29 It has been suggested that the contractile vacuole could be an evolutionary precursor to the recycling endosomal system in other eukaryotes.30,31 Recently, the participation of Rab32 (present in the contractile vacuole) in the biogenesis of the acidocalcisome was suggested.23 Evidence of acidocalcisome-contractile vacuole fusion was also observed25 and advances in ultrastructural techniques have allowed the observation of intimate contact between structures, such as the contractile vacuole, the acidocalcisome, and the spongiome (Fig. 18.8)23,32

D model of the contractile vacuole and flagellar pocket showing the interconnected spongiome connected to the contractile vacuole

Figure 18.8 3D model of the contractile vacuole and flagellar pocket showing the interconnected spongiome connected to the contractile vacuole (arrows) and concentrated in the anterior region of the contractile vacuole. Some vesicles were also connected to the spongiome (arrowheads).

Source: After Girard-Dias W, Alcantara CL, Cunha-e-Silva N, de Souza W, Miranda K. On the ultrastructural organization of Trypanosoma cruzi using cryopreparation methods and electron tomography. Histochem Cell Biol 2012;138(6):821—31.

 
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