Zhuang Z, Linser P J, Harvey W R
The Whitney Laboratory, University of Florida, St Augustine, FL 32086, USA.
J Exp Biol. 1999 Sep;202(Pt 18):2449-60. doi: 10.1242/jeb.202.18.2449.
The pH profile, gross structure, ultrastructure and immunolabeling of the mosquito (Aedes aegypti) larval midgut are described as a first step in analyzing the role of plasma membrane H(+ )V-ATPase in the alkalization of the gut, nutrient uptake and ionic regulation. Binding of an antibody to H(+ )V-ATPase subunit E colocalizes with 'portasomes' (approximately 10 nm in diameter), which are thought to correspond to the V(1) part of the H(+) V-ATPase. In gastric caeca (pH 8), both antibody-binding sites and portasomes are located apically; in the anterior midgut (pH 10-11), they are located basally; and in the posterior midgut (pH approximately equal to 8) they are again located apically. The hypothesis that the energization of alkalization is mediated by an H(+) V-ATPase is supported by the inability of larvae to maintain the high pH after 72 h in 10 (micro)M bafilomycin B1. Confirming earlier reports, the two principal epithelial cell types are designated as 'columnar' and 'cuboidal' cells. The apical plasma membranes (microvilli) of epithelial cells in the gastric caeca and basal infoldings of anterior midgut are invaded by mitochondria that lie within approximately 20 nm of the portasome-studded plasma membranes. The colocalization of V-ATPase-immunolabeling sites and portasomes to specific plasma membranes within so-called 'mitochondria-rich' cells of gastric caeca and anterior midgut suggests that midgut alkalization in mosquitoes is achieved by molecular mechanisms similar to those that have been described in caterpillars, even though the gross structure of the midgut and the localization of the V-ATPase are dissimilar in the two species. In caterpillars, the high alkalinity is thought to break down dietary tannins, which block nutrient absorption; it may play a similar role in plant-detritus-feeding mosquito larvae. The colocalization of immunolabeling sites and portasomes, together with the presence of long, 'absorptive-type' microvilli in the posterior midgut, suggest that the V-ATPase energizes nutrient uptake there.
描述了埃及伊蚊幼虫中肠的pH分布、大体结构、超微结构和免疫标记，作为分析质膜H(+)V - ATP酶在肠道碱化、营养吸收和离子调节中作用的第一步。抗H(+)V - ATP酶亚基E抗体的结合与“孔体”（直径约10纳米）共定位，孔体被认为对应于H(+)V - ATP酶的V(1)部分。在胃盲囊（pH 8）中，抗体结合位点和孔体都位于顶端；在前肠中部（pH 10 - 11），它们位于基部；而在后肠中部（pH约等于8），它们又位于顶端。幼虫在10（微）摩尔巴弗洛霉素B1中72小时后无法维持高pH值，这支持了碱化的能量供应由H(+)V - ATP酶介导的假说。证实早期报告，两种主要上皮细胞类型被指定为“柱状”和“立方”细胞。胃盲囊中上皮细胞的顶端质膜（微绒毛）和前肠中部的基部内褶被线粒体侵入，线粒体位于布满孔体的质膜约20纳米范围内。胃盲囊和前肠中部所谓“富含线粒体”细胞内V - ATP酶免疫标记位点和孔体与特定质膜的共定位表明，蚊子中肠碱化是通过与毛虫中描述的类似分子机制实现的，尽管中肠的大体结构和V - ATP酶的定位在这两个物种中不同。在毛虫中，高碱度被认为可分解阻碍营养吸收的膳食单宁；它可能在以植物碎屑为食的蚊子幼虫中起类似作用。免疫标记位点和孔体的共定位，以及后肠中部存在长的“吸收型”微绒毛，表明V - ATP酶为那里的营养吸收提供能量。
