INVESTIGATION OF SALT CONCENTRATION IN THE AIRWAY SURFACE LIQUID USING X-RAY FLU

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. There is no cure for Cystic Fibrosis (CF), a lethal disease that affects 1 of every 3,000 live births in the U.S. In CF, mutations in the cystic fibrosis transmembrane conductance regulator (CFTR), a Cl ion channel found in the apical membranes of secretory epithelial cells, disrupt epithelial ion transport and result in the accumulation of viscous infected mucus in pulmonary airways which lead to respiratory failure. The degree of mucus hydration, which determines the mucus viscosity, is abnormal in CF, and a number of competing explanations have been proposed. The only way to discriminate between these different mechanisms is a measurement of the salt level in the airway surface liquid (ASL), a 10 micron thick layer of fluid covering airway epithelial cells, to see if it has been increased or decreased relative to normal levels. Although this is the most important open question in CF, it is extremely difficult to answer reliably. A number of approaches have been attempted, such as conductivity measurements, direct ASL removal, and fluorescent chelation compounds as ion concentration indicators, but the results vary over an order of magnitude. The principal difficulty lies in the fact that any contact measurement will induce a dramatic increase in fluid secretion and change the measured salt concentration. We propose a synchrotron-based non-contact measurement of the salt level in the ASL. We are the only group that has successfully cultured human airway epithelial cell lines both with and without the CF defect. These samples can be mounted on custom-made culture plates. Using GXF, grazing x-ray fluorescence, it will be possible to simultaneously monitor the concentrations of all the relevant ion species involved in the CF pathogenesis, and establish the sequence of molecular events which is responsible for the disease for the first time, as well as detailed pharmacological studies.