Schwab J C, Beckers C J, Joiner K A
Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06510-8056.
Proc Natl Acad Sci U S A. 1994 Jan 18;91(2):509-13. doi: 10.1073/pnas.91.2.509.
The obligate intracellular protozoan parasite Toxoplasma gondii creates and enters into a unique membrane-bounded cytoplasmic compartment, the parasitophorous vacuole, when invading mammalian host cells. By microinjecting polar fluorescent molecules into individual T. gondii-infected fibroblasts, we show here that the parasitophorous vacuole membrane (PVM) surrounding the parasite functions as a molecular sieve. Lucifer yellow (457 Da) displayed free bidirectional flux across the PVM and distinctly outlined the parasites, which did not take up the dye, within the vacuole. This dye movement was not appreciably delayed by pretreatment of cells with 5 mM probenecid or chilling the monolayer to 5 degrees C, suggesting that dye movement was due to passive permeation through a membrane pore rather than active transport. Calcein, fluo-3, and a series of fluorescein isothiocyanate-labeled peptides up to 1291 Da crossed the PVM in a size-restricted fashion. A labeled peptide of 1926 Da and labeled dextrans and proteins (> or = 3000 Da) failed to transit the PVM. This putative channel in the PVM therefore allows exchange of molecules up to 1300-1900 Da between the host cell cytoplasm and the parasitophorous vacuolar space.
专性细胞内原生动物寄生虫刚地弓形虫在侵入哺乳动物宿主细胞时，会形成并进入一个独特的膜结合细胞质区室，即寄生泡。通过将极性荧光分子显微注射到单个刚地弓形虫感染的成纤维细胞中，我们在此表明，围绕寄生虫的寄生泡膜（PVM）起到分子筛的作用。荧光素黄（457道尔顿）在PVM上表现出自由的双向通量，并清晰勾勒出泡内未摄取染料的寄生虫轮廓。用5 mM丙磺舒预处理细胞或将单层细胞冷却至5℃，这种染料的移动并未明显延迟，这表明染料的移动是由于通过膜孔的被动渗透而非主动运输。钙黄绿素、氟钙素-3以及一系列分子量高达1291道尔顿的异硫氰酸荧光素标记肽以大小受限的方式穿过PVM。一个1926道尔顿的标记肽以及标记的葡聚糖和蛋白质（≥3000道尔顿）未能穿过PVM。因此，PVM中的这种假定通道允许分子量高达1300 - 1900道尔顿的分子在宿主细胞质和寄生泡空间之间交换。
