Motile Cilia of Human Airway Epithelia Are Chemosensory

Beat It Primary cilia are specialized organelles that serve important sensory functions in many different tissues and cells, and defects in their structure and function underlie a variety of genetic diseases. In contrast to primary cilia, motile cilia serve a mechanical function. For example, the cilia on airway epithelia remove inhaled material from the lung. Shah et al. (p. 1131, published online 23 July; see the cover; see the Perspective by Kinnamon and Reynolds) now show that these classic motile cilia are also chemosensory. The motile cilia on airway epithelia contain bitter-taste receptors and their associated signaling machinery. Moreover, application of bitter substances triggers an elevation of intracellular Ca2+ levels and increases cilia beat frequency. Thus, in airway epithelia, bitter-taste receptors may be able to detect noxious substances entering the airways and initiate an autonomous defensive mechanism designed to accelerate elimination of the offending compound. Airway epithelia directly sense and respond to noxious substances. Cilia are microscopic projections that extend from eukaryotic cells. There are two general types of cilia; primary cilia serve as sensory organelles, whereas motile cilia exert mechanical force. The motile cilia emerging from human airway epithelial cells propel harmful inhaled material out of the lung. We found that these cells express sensory bitter taste receptors, which localized on motile cilia. Bitter compounds increased the intracellular calcium ion concentration and stimulated ciliary beat frequency. Thus, airway epithelia contain a cell-autonomous system in which motile cilia both sense noxious substances entering airways and initiate a defensive mechanical mechanism to eliminate the offending compound. Hence, like primary cilia, classical motile cilia also contain sensors to detect the external environment.

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