Desai S A, Bezrukov S M, Zimmerberg J
The Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Nature. 2000 Aug 31;406(6799):1001-5. doi: 10.1038/35023000.
Growth of the malaria parasite in human red blood cells (RBCs) is accompanied by an increased uptake of many solutes including anions, sugars, purines, amino acids and organic cations. Although the pharmacological properties and selectivity of this uptake suggest that a chloride channel is involved, the precise mechanism has not been identified. Moreover, the location of this uptake in the infected RBC is unknown because tracer studies are complicated by possible uptake through fluid-phase pinocytosis or membranous ducts. Here we have studied the permeability of infected RBCs using the whole-cell voltage-clamp method. With this method, uninfected RBCs had ohmic whole-cell conductances of less than 100 pS, consistent with their low tracer permeabilities. In contrast, trophozoite-infected RBCs exhibited voltage-dependent, non-saturating currents that were 150-fold larger, predominantly carried by anions and abruptly abolished by channel blockers. Patch-clamp measurements and spectral analysis confirmed that a small (< 10 pS) ion channel on the infected RBC surface, present at about 1,000 copies per cell, is responsible for these currents. Because its pharmacological properties and substrate selectivities match those seen with tracer studies, this channel accounts for the increased uptake of small solutes in infected RBCs. The surface location of this new channel and its permeability to organic solutes needed for parasite growth indicate that it may have a primary role in a sequential diffusive pathway for parasite nutrient acquisition.
疟原虫在人类红细胞（RBCs）内生长时，会伴随着许多溶质摄取量的增加，这些溶质包括阴离子、糖类、嘌呤、氨基酸和有机阳离子。尽管这种摄取的药理学特性和选择性表明涉及一种氯离子通道，但具体机制尚未明确。此外，由于示踪剂研究因可能通过液相胞饮作用或膜性管道摄取而变得复杂，所以这种摄取在受感染红细胞中的位置尚不清楚。在这里，我们使用全细胞膜片钳方法研究了受感染红细胞的通透性。使用这种方法，未受感染的红细胞具有小于100 pS的欧姆全细胞电导，这与其低示踪剂通透性一致。相比之下，滋养体感染的红细胞表现出电压依赖性、非饱和电流，其电流大150倍，主要由阴离子携带，并被通道阻滞剂突然阻断。膜片钳测量和光谱分析证实，受感染红细胞表面存在一个小的（<10 pS）离子通道，每个细胞约有1000个拷贝，是这些电流的原因。由于其药理学特性和底物选择性与示踪剂研究中观察到的相匹配，这个通道解释了受感染红细胞中小溶质摄取量的增加。这个新通道的表面位置及其对寄生虫生长所需有机溶质的通透性表明，它可能在寄生虫获取营养的连续扩散途径中起主要作用。
