Department of Biology, University of Konstanz, P.O. Box 5560, 78457 Konstanz, Germany.
Cell Calcium. 2012 May;51(5):351-82. doi: 10.1016/j.ceca.2012.01.006. Epub 2012 Mar 3.
The importance of Ca2+-signaling for many subcellular processes is well established in higher eukaryotes, whereas information about protozoa is restricted. Recent genome analyses have stimulated such work also with Alveolates, such as ciliates (Paramecium, Tetrahymena) and their pathogenic close relatives, the Apicomplexa (Plasmodium, Toxoplasma). Here we compare Ca2+ signaling in the two closely related groups. Acidic Ca2+ stores have been characterized in detail in Apicomplexa, but hardly in ciliates. Two-pore channels engaged in Ca2+-release from acidic stores in higher eukaryotes have not been stingently characterized in either group. Both groups are endowed with plasma membrane- and endoplasmic reticulum-type Ca2+-ATPases (PMCA, SERCA), respectively. Only recently was it possible to identify in Paramecium a number of homologs of ryanodine and inositol 1,3,4-trisphosphate receptors (RyR, IP3R) and to localize them to widely different organelles participating in vesicle trafficking. For Apicomplexa, physiological experiments suggest the presence of related channels although their identity remains elusive. In Paramecium, IP3Rs are constitutively active in the contractile vacuole complex; RyR-related channels in alveolar sacs are activated during exocytosis stimulation, whereas in the parasites the homologous structure (inner membrane complex) may no longer function as a Ca2+ store. Scrutinized comparison of the two closely related protozoan phyla may stimulate further work and elucidate adaptation to parasitic life. See also "Conclusions" section.
在高等真核生物中，Ca2+信号对于许多亚细胞过程的重要性已得到充分证实，而关于原生动物的信息则较为有限。最近的基因组分析也刺激了对纤毛类（如草履虫、四膜虫）及其致病近亲——顶复门（疟原虫、弓形虫）等有孔虫的此类研究。在这里，我们比较了这两个密切相关的群体中的 Ca2+信号。在顶复门中，酸性 Ca2+库已被详细描述，但在纤毛类中几乎没有。在高等真核生物中参与从酸性库中释放 Ca2+的双孔通道在这两个群体中都没有被严格描述。这两个群体分别具有质膜型和内质网型 Ca2+-ATP 酶（PMCA、SERCA）。直到最近，才有可能在草履虫中鉴定出许多肌醇 1,4,5-三磷酸受体（IP3R）和 Ryanodine 受体（RyR）的同源物，并将它们定位到参与囊泡运输的广泛不同的细胞器中。对于顶复门，生理实验表明存在相关通道，尽管它们的身份仍难以捉摸。在草履虫中，IP3R 在伸缩泡复合物中持续活跃；肺泡囊中与 RyR 相关的通道在胞吐刺激时被激活，而在寄生虫中，同源结构（内膜复合物）可能不再作为 Ca2+库发挥作用。对这两个密切相关的原生动物门的仔细比较可能会刺激进一步的研究，并阐明对寄生生活的适应。另见“结论”部分。
