Department of Physiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Department of Physiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
Am J Physiol Regul Integr Comp Physiol. 2014 Oct 1;307(7):R828-36. doi: 10.1152/ajpregu.00561.2013. Epub 2014 Jul 9.
Rhodnius prolixus is a hematophagous insect vector of Chagas disease capable of ingesting up to 10 times its unfed body weight in blood in a single meal. The excess water and ions ingested with the meal are expelled through a rapid postprandial diuresis driven by the Malpighian tubules. Diuresis is triggered by at least two diuretic hormones, a CRF-related peptide and serotonin, which were traditionally believed to trigger cAMP as an intracellular second messenger. Recently, calcium has been suggested to act as a second messenger in serotonin-stimulated Malpighian tubules. Thus, we tested the role of calcium in serotonin-stimulated Malpighian tubules from R. prolixus. Our results show that serotonin triggers cAMP-mediated intracellular Ca(2+) waves that were blocked by incubation in Ca(2+)-free saline containing the cell membrane-permeant Ca(2+) chelator BAPTA-AM, or the PKA blocker H-89. Treatment with 8-Br-cAMP triggered Ca(2+) waves that were blocked by H-89 and BAPTA-AM. Analysis of the secreted fluid in BAPTA-AM-treated tubules showed a 75% reduction in fluid secretion rate with increased K(+) concentration, reduced Na(+) concentration. Taken together, the results indicate that serotonin triggers cAMP and PKA-mediated Ca(2+) waves that are required for maximal ion transport rate.
吸血昆虫传播恰加斯病的罗得西亚锥虫能够在单次进食中摄入相当于其未进食体重 10 倍的血液量。进食过程中摄入的多余水分和离子通过马尔皮基氏管（Malpighian tubules）驱动的餐后快速利尿作用排出体外。至少有两种利尿激素（一种与 CRF 相关的肽和血清素）触发了利尿作用，它们传统上被认为通过细胞内第二信使 cAMP 发挥作用。最近，有人提出钙作为血清素刺激的马尔皮基氏管中的第二信使发挥作用。因此，我们测试了钙在罗得西亚锥虫的血清素刺激的马尔皮基氏管中的作用。我们的结果表明，血清素触发 cAMP 介导的细胞内 Ca(2+)波，该波被在含有细胞膜通透型 Ca(2+)螯合剂 BAPTA-AM 的无钙盐水中孵育或 PKA 抑制剂 H-89 阻断。8-Br-cAMP 的处理引发了 Ca(2+)波，该波被 H-89 和 BAPTA-AM 阻断。在 BAPTA-AM 处理的管腔中分泌的液体分析显示，随着 K(+)浓度的增加和 Na(+)浓度的降低，分泌速率降低了 75%。综上所述，结果表明，血清素触发 cAMP 和 PKA 介导的 Ca(2+)波，这是最大离子转运速率所必需的。
