Harvey W R, Cioffi M, Dow J A, Wolfersberger M G
J Exp Biol. 1983 Sep;106:91-117. doi: 10.1242/jeb.106.1.91.
K+ transport by the epithelia of midgut, salivary glands, Malpighian tubules, sensory sensilla, possibly rectum, and other organs of certain insects appears to use a unique K+ ATPase. Ouabain inhibition of transport-related events has not been demonstrated in these epithelia. The K+ pump is unlike the Na-K;ump but resembles the H;ump of phosphorylating membranes in its transport orientation, efficient thermodynamics, speculated two K+ per one MgATP2- stoichiometry, electrogenicity, and structure. Older electrochemical, tracer flux, and conductance evidence suggested that the K+ pump was on the apical plasma membrane of transporting cells in these epithelia. New X-ray microanalytical studies (XMA), reveal that the K+ concentration in all cells is more than 100 mM. Together with new microelectrode data these XMA results confirm the apical K+ pump location, resolve the K+ transport sport route, and suggest that the goblet cell cavity facilitates the generation of a large apical PD which may be used in nutrient absorption and pH regulation. K+ portasomes, which resemble F1-Fo ATPase particles, stud these K+ transporting apical membranes and are though to be the unit of active K+ transport. We have suggested a K+ transport mechanism in which two cations (2K+) are abandoned in an isolated domain of the portasomes during ATP2-hydrolysis and are repelled to the opposite membrane side via a K+ channel. Small peptides hydrolysed from the delta-endotoxin of Bacillus thuringiensis inhibit the K+ transport and may be useful as K+ pump inhibitors, apical membrane probes and insecticides. Goblet cell apical membrane fragments (GCAM) as well as fragments from columnar cell apical membrane (CCAM), lateral membrane (LM) and basal membranes (BM) were isolated as clean fractions using ultrasound, aspiration, and both differential and density gradient centrifugation; purification was monitored by electron microscopy. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE) reveals that GCAM, CCAM, LM and BM have very different protein compositions. Preliminary enzymology is consistent with the K+ ATPase being on the apical plasma membrane of the goblet cells of midgut and enveloping cells of sensilla.
某些昆虫的中肠、唾液腺、马氏管、感觉器、可能还有直肠及其他器官的上皮细胞对钾离子的转运似乎利用了一种独特的钾离子ATP酶。哇巴因对这些上皮细胞中与转运相关事件的抑制作用尚未得到证实。钾离子泵与钠钾泵不同，但在转运方向、有效热力学、推测的每一个MgATP2-对应两个钾离子的化学计量、电生性及结构方面，类似于磷酸化膜的氢离子泵。早期的电化学、示踪剂通量及电导证据表明，钾离子泵位于这些上皮细胞中进行转运的细胞的顶端质膜上。新的X射线微分析研究（XMA）显示，所有细胞中的钾离子浓度均超过100 mM。这些XMA结果与新的微电极数据一起，证实了顶端钾离子泵的位置，解析了钾离子转运途径，并表明杯状细胞腔有助于产生较大的顶端跨膜电位差，这可能用于营养物质吸收和pH调节。类似于F1-Fo ATP酶颗粒的钾离子孔体密布于这些进行钾离子转运的顶端膜上，被认为是钾离子主动转运的单位。我们提出了一种钾离子转运机制，即在ATP2水解过程中，两个阳离子（2K+）在孔体的一个孤立区域被释放，并通过一个钾离子通道被排斥到相对的膜侧。从苏云金芽孢杆菌的δ-内毒素水解得到的小肽可抑制钾离子转运，可能用作钾离子泵抑制剂、顶端膜探针和杀虫剂。利用超声、抽吸以及差速离心和密度梯度离心，将杯状细胞顶端膜片段（GCAM）以及柱状细胞顶端膜（CCAM）、侧膜（LM）和基底膜（BM）的片段分离为纯净组分；通过电子显微镜监测纯化过程。十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS PAGE）显示，GCAM、CCAM、LM和BM具有非常不同的蛋白质组成。初步酶学研究结果与钾离子ATP酶位于中肠杯状细胞和感觉器包被细胞的顶端质膜上这一观点一致。
