Kolosov Dennis, O'Donnell Michael J
Department of Biological Sciences, California State University San Marcos, 333 S Twin Oaks Valley Road, San Marcos, CA 92096, USA.
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada, L8S 4K1.
J Exp Biol. 2022 Feb 15;225(Suppl1). doi: 10.1242/jeb.243293. Epub 2022 Feb 4.
This Review addresses the means by which epithelia change the direction of vectorial ion transport. Recent studies have revealed that insect Malpighian (renal) tubules can switch from secreting to reabsorbing K+. When the gut of larval lepidopterans is empty (during the moult cycle) or when the larvae are reared on K+-deficient diet, the distal ileac plexus segment of the tubule secretes K+ from the haemolymph into the tubule lumen. By contrast, in larvae reared on K+-rich diet, ions and fluid are reabsorbed from the rectal lumen into the perinephric space surrounding the cryptonephridial tubules of the rectal complex. Ions and fluid are then transported from the perinephric space into the lumen of the cryptonephridial tubules, thus supplying the free segments of the tubule downstream. Under these conditions, some of the K+ and water in the tubule lumen is reabsorbed across the cells of the distal ileac plexus, allowing for expansion of haemolymph volume in the rapidly growing larvae, as well as recycling of K+ and base equivalents. RNA sequencing data reveal large-scale changes in gene transcription that are associated with the switch between ion secretion and ion reabsorption by the distal ileac plexus. An unexpected finding is the presence of voltage-gated, ligand-gated and mechanosensitive ion channels, normally seen in excitable cells, in Malpighian tubules. Transcriptomic surveys indicate that these types of channels are also present in multiple other types of vertebrate and invertebrate epithelia, suggesting that they may play novel roles in epithelial cell signalling and regulation of epithelial ion transport.
本综述探讨上皮细胞改变矢量离子转运方向的方式。最近的研究表明，昆虫马氏（肾）管可以从分泌钾离子转变为重吸收钾离子。当鳞翅目幼虫的肠道为空（在蜕皮周期中）或幼虫以低钾饮食饲养时，马氏管的远端回肠丛段会将血淋巴中的钾离子分泌到管腔中。相比之下，在以高钾饮食饲养的幼虫中，离子和液体从直肠腔被重吸收到围绕直肠复合体隐肾管的围肾空间。然后离子和液体从围肾空间被转运到隐肾管腔，从而为下游的游离管段提供物质。在这些条件下，管腔中的一些钾离子和水会通过远端回肠丛的细胞被重吸收，这有助于快速生长的幼虫血淋巴体积的增加，以及钾离子和碱基当量的循环利用。RNA测序数据揭示了与远端回肠丛离子分泌和离子重吸收转换相关的大规模基因转录变化。一个意外的发现是在马氏管中存在通常在可兴奋细胞中见到的电压门控、配体门控和机械敏感离子通道。转录组学调查表明，这些类型的通道也存在于多种其他类型的脊椎动物和无脊椎动物上皮中，这表明它们可能在上皮细胞信号传导和上皮离子转运调节中发挥新的作用。
