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A new study from the University of Iowa found that pulmonary ionocytes, which are rare lung cells, aid in the absorption of water and salt from the airway surface. This cell behaviour is the polar opposite of what was expected, and it could have implications for cystic fibrosis (CF) lung disease.
Scientists discovered ionocytes, a type of cell seen in fish gills and frog skin, in the lining of human lungs and airways five years ago. These pulmonary ionocytes piqued the interest of cystic fibrosis researchers because, despite accounting for only about 1% of all cells in the airway lining, they carry around half of the total amount of CFTR, the protein that is faulty in cystic fibrosis. CFTR channels that are present in airway secretory cells are known to secrete chloride ions out of the cell and into the thin layer of liquid that covers the airway surface. This airway surface liquid plays a vital role in defending the lungs against harmful germs and particles. Because water "follows" salt, the outflow of chloride ions promotes hydration of the airway surface. In contrast, the new study found that CFTR channels in ionocytes do the opposite; they absorb chloride ions and promote moisture absorption. "The key feature that allows ionocytes to absorb chloride is the ionocyte-specific barttin chloride channel on the opposite membrane of the cell from the CFTR channel," says Ian Thornell, PhD, UI research assistant professor of internal medicine and senior author of the new study published in the Oct 16 issue of The Journal of Clinical Investigation. "Together, these two channels form a conduit for chloride through the ionocyte that helps drain the liquid lining the airways into the body." (ANI)
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