Division of Nephrology and Hypertension, Department of Medicine, University of Florida-Jacksonville, Jacksonville, FL 32206, USA.
J Insect Physiol. 2012 Apr;58(4):570-9. doi: 10.1016/j.jinsphys.2011.12.009. Epub 2011 Dec 21.
The newly identified metazoan Na(+)/H(+) antiporter (NHA) family is represented by two paralogues, AgNHA1 and AgNHA2, in the genome of the African malaria mosquito, Anopheles gambiae. Both antiporters are postulated to be electrophoretic i.e. voltage-driven. AgNHA1 was first cloned from An. gambiae larvae and immunolocalized with respect to the H(+) V-ATPase by the Harvey laboratory. Little is known about the properties of NHA1s; attempts to characterize AgNHA1 in Na(+)/H(+) exchanger (NHE)-lacking Chinese hamster ovary cells and in yeast cells or frog oocytes were unsuccessful. Even less is known about AgNHA2. It is predicted to have a relative molecular mass of ∼60 kDa and shares 30.5% amino acid identity with AgNHA1. Immunolocalization images show AgNHA2 on the apical plasma membrane of stellate cells in Malpighian tubules of An. gambiae larvae and adults. When heterologously expressed in a mutant strain of the yeast, Saccharomyces cerevisiae, which lacks endogenous cation/proton antiporters and pumps, AgNHA2 enhanced repression of growth by the alkali metal cations, Li(+), Na(+), or K(+) and enhanced Li(+) accumulation. The yeast growth studies invite the speculation that AgNHA2 is an electrophoretic antiporter with a stoichiometry of nNa(+) to 1H(+) with n > 1. Immunolocalization images provide direct evidence that H(+) V-ATPase is co-localized with AgNHA1 on the apical membrane of principal cells but it is not present in the stellate cells where AgNHA2 is localized apically. These results are consistent with the notion that the outside positive voltage that the H(+) V-ATPase generates across the apical membrane of principal cells appears with but little attenuation across the apical membrane of stellate cells. This immunolocalization pattern is consistent with the hypothesis that the voltage acts via AgNHA1 to drive nH(+) into the principal cells and Na(+) out to the lumen and acts via AgNHA2 to drive nNa(+) into the stellate cells and H(+) out to the lumen. Precious Na(+) is then retained by ejection into the blood via a basal Na(+)/K(+)-ATPase. Localizations of anion transporters and their functions in stellate and principal cells are described by Linser, Romero and associates in this volume. The role that the electrogenic H(+) V-ATPase and the electrophoretic cationic and anionic transporters play in ion homeostasis is incorporated into a model for Malpighian tubule cells of larval mosquitoes.
新鉴定的后生动物 Na(+)/H(+) 反向转运蛋白 (NHA) 家族在非洲疟蚊 Anopheles gambiae 的基因组中由两个旁系同源物 AgNHA1 和 AgNHA2 代表。这两种反向转运蛋白都被假定为电泳的，即电压驱动的。AgNHA1 最初是从 An. gambiae 幼虫中克隆出来的，并由 Harvey 实验室通过免疫荧光定位到 H(+) V-ATPase。关于 NHA1s 的特性知之甚少；试图在缺乏 Na(+)/H(+) 交换器 (NHE) 的中国仓鼠卵巢细胞和酵母细胞或蛙卵母细胞中表征 AgNHA1 的尝试均未成功。关于 AgNHA2 知之甚少。它预计具有相对分子质量约 60 kDa，并与 AgNHA1 共享 30.5%的氨基酸同一性。免疫荧光定位图像显示 AgNHA2 位于 An. gambiae 幼虫和成虫的星状细胞的顶质膜上。当在缺乏内源性阳离子/质子反向转运体和泵的酵母突变株 Saccharomyces cerevisiae 中异源表达时，AgNHA2 增强了碱金属阳离子 Li(+)、Na(+)或 K(+)的生长抑制作用，并增强了 Li(+)的积累。酵母生长研究引发了这样的推测，即 AgNHA2 是一种电泳反向转运体，具有 nNa(+) 对 1H(+) 的化学计量比，其中 n > 1。免疫荧光定位图像提供了直接证据，表明 H(+) V-ATPase 与主细胞的顶质膜上的 AgNHA1 共定位，但不存在于星状细胞中，AgNHA2 位于顶质膜的顶端。这些结果与这样的观点一致，即 H(+) V-ATPase 在主细胞顶质膜上产生的外部正电压几乎没有衰减地穿过星状细胞的顶质膜。这种免疫定位模式与假设一致，即电压通过 AgNHA1 将 nH(+) 驱动到主细胞中，将 Na(+) 驱动到腔中，并通过 AgNHA2 将 nNa(+) 驱动到星状细胞中，并将 H(+) 驱动到腔中。然后通过基底 Na(+)/K(+)-ATPase 将宝贵的 Na(+) 排出到血液中。阴离子转运体的定位及其在星状细胞和主细胞中的功能由 Linser、Romero 及其同事在本卷中描述。电致的 H(+) V-ATPase 和电泳阳离子和阴离子转运体在离子稳态中的作用被纳入到幼虫蚊子的马氏管细胞模型中。
