Lungs with taste buds? You'd bitter believe it - Scientists have discovered that it's not just the tongue that's endowed with taste buds - cells lining the lung have them too. Writing in Science, University of Iowa researcher Alok Shah and his colleagues explain how they initially suspected that lung cells might be able to detect the presence of harmful substances within inhaled air and that this might trigger enhanced self-cleaning measures such as the production of more mucus.
To test the theory the team used in vitro genetic techniques to study which genes were being turned on in the cells lining the airways. Remarkably they found that thin hair-like extensions called cilia, which are on the airway cells' surfaces and make beating movements to move mucus out of the lungs, are equipped with the same family of chemical receptors that enable the tongue to taste bitter flavours. Only the cilia carry these receptors but the team found that when they are activated by adding bitter-flavoured chemicals the levels of calcium in the cilia-bearing cells shoots up.
This acts as a signal that the cells then pass amongst themselves via connections between adjacent cells called gap junctions. In this way the lining of the airway is able to orchestrate a response to the presence of potential toxins, inhaled chemicals and infections. The team also point out that certain bacteria, including Pseudomonas aeruginosa which is a major problem in cystic fibrosis patients, produce chemical signalling molecules called lactones, which can also activate these receptors. At the same time the discovery might also account for some of the damaging effects of cigarette smoking.
Nicotine is a characteristically bitter-tasting alkaloid and smoking frequently leads to cilia loss, which in turns hampers lung defenses. It could be that both of these effects are consequences of over-stimulation of these receptors and that perhaps blocking them can help to mitigate or reverse the damage. The next step will now be to study how this system functions in vivo to keep lungs clean and how it might be manipulated.