Malpighian Tubule Transport Physiology: Mechanism and Regulation

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This proposal aims to bring genetics, molecular biology and classical physiology to bear on questions of epithelial transport in Malpighian tubules, the kidneys of insects. Studies of adult mosquito Malpighian tubules in the lab of the principal investigator Beyenbach have uncovered new transport phenomena that stimulate research of epithelial transport in biological systems beyond insects. For example, his finding in Malpighian tubules of a) the energizing of diverse epithelial transport systems with the V-type H+ ATPase and not the Na/K ATPase, b) the channel-like behavior of septate (tight) junctions, and c) the rapid regulation of paracellular permeability in the astonishing time domain of seconds, are motivating searches for similar phenomena in vertebrate tissues. The present proposal is a logical extension of the above findings. Hypothesis-driven experiments promise to discover new transport systems while exploring new ideas in transport physiology. In Aim 1, the functional characterization of NHE8 (a Na-H transport protein) he has already cloned in Aedes Malpighian tubules may uncover the first electrogenic Na/H exchanger in any tissue, vertebrate or invertebrate. Aim 2 applies proteomics and highly sensitive mass spec methods with the promise of identifying not only NHE8 but also new proteins, and potentially important new transporters in the apical membrane of the adult Malpighian tubule. In Aim 3 he seeks to a) identify gap junctions, b) determine size and charge selectivity, c) explore the role of gap junctions in cell-to-cell transmission of Ca2+ waves that may mediate the signal transduction of leucokinin, and d) test the novel idea of the metabolic regulation of gap junctions. Three collaborators with an international reputation in molecular biology (Wieczorek), intracellular Ca2+ imaging (Walz), and proteomics (Schooley) have committed their labs to the success of this project. What has motivated this collaboration is the deep understanding that derives from illuminating important research questions from diverse perspectives. Broader Impact. The PI is an enthusiastic teacher and mentor whose lab attracts some of the most gifted and motivated undergraduates. Many make a lifetime commitment to research. As many as 46 undergraduates have been trained in his lab alongside graduate students and post-docs; 19 undergraduates share authorship in refereed journals. Many undergraduates have been accepted in MD-PhD programs, and some have now their own research laboratories. Wanting to know is a powerful drive, perhaps the strongest motivation of the PI and his students. The PI teaches a popular elective Biology course on campus- Mammalian Physiology -to seniors and graduate students. He serves as Director of the Cornell program of study Undergraduate Physiology. The PI is active in international education, helping US students secure summer research positions in Germany, and assisting German students find research opportunities or clinical rotations in the US. The PI is a founding member of the Alexander von Humboldt Association of America (www.avhaa.org). He has received the highest German civilian award, the Bundesverdienstkreuz, for fostering international cooperation in education and research.