Lefurgey Ann, Gannon Melissa, Blum Joseph, Ingram Peter
Durham Veterans Affairs Medical Center, Duke University Medical Center, Durham, NC 27705, USA.
J Eukaryot Microbiol. 2005 May-Jun;52(3):277-89. doi: 10.1111/j.1550-7408.2005.00030.x.
The protozoan parasite Leishmania donovani encounters large fluctuations in osmolality as it cycles between its insect vector and human host. The flagellated promastigote exhibits regulatory volume responses involving organic and inorganic osmolytes, but little is known about volume regulation in the clinically relevant amastigote that multiplies within the parasitophorous vacuoles of mammalian host cells. Using a combination of morphological, X-ray microanalytical, and biochemical approaches we determined that non-motile amastigotes respond to hypotonic stress with (1) an amino acid and l-alanine-mediated regulatory volume decrease, and (2) a parallel release of Na+, K+, P (presumably as negatively charged phosphates), and subsequently Cl- from cytoplasm and the cell as a whole. In addition P, Zn2+, and subsequently Ca2+ increase in acidocalcisomes as Cl- content declines in this compartment. This evidence is the first to document subcellular translocation of, and thus a potential role for, zinc in volume regulatory responses. These coordinated changes in organic and inorganic osmolytes demonstrate that amastigote subcellular compartments, particularly acidocalcisomes, function in maintaining ionic homeostasis in the response of Leishmania amastigotes to hypo-osmotic stress.
原生动物寄生虫杜氏利什曼原虫在其昆虫媒介和人类宿主之间循环时，会遇到渗透压的大幅波动。有鞭毛的前鞭毛体表现出涉及有机和无机渗透剂的调节性容积反应，但对于在哺乳动物宿主细胞的寄生泡内增殖的临床相关无鞭毛体的容积调节知之甚少。我们结合形态学、X射线微分析和生化方法确定，不活动的无鞭毛体对低渗应激的反应为：（1）由氨基酸和L-丙氨酸介导的调节性容积减小；（2）Na⁺、K⁺、P（可能以带负电荷的磷酸盐形式）以及随后Cl⁻从细胞质和整个细胞中平行释放。此外，随着酸性钙小体中Cl⁻含量下降，该细胞器中的P、Zn²⁺以及随后的Ca²⁺增加。这一证据首次证明了锌在容积调节反应中的亚细胞转运及其潜在作用。有机和无机渗透剂的这些协调变化表明，无鞭毛体的亚细胞区室，特别是酸性钙小体，在利什曼原虫无鞭毛体对低渗应激的反应中发挥维持离子稳态的作用。
