It's well-known that human tongues can taste five sensations – sweet, salt, bitter,sour and the mysterious umami. This is due to different molecular receptors in our tastebuds. But research from scientists in the US has shown that bitter taste receptors actually play a role in our lungs as well as our tongues – and it could lead to new ways to treat asthma and other lung diseases that affect around 300 million people around the world, including me!
This work builds on a discovery we covered on the show back in 2009, where researchers first discovered that the same receptors that detect bitter tastes on our tongues could also be found in our lungs, lurking on special hairy cells that line the airways. It's thought that they're there to detect nasty stuff in the air we breathe, and stimulate the lungs to get rid of them, for example by producing more phlegm. Now Stephen Liggett and his team at the University of Maryland have published a paper in the journal Nature Medicine showing that the same bitter receptors can be found in airway muscle cells too.
The researchers thought that stimulating these bitter receptors with bitter chemicals might cause muscle cells to contract, narrowing the airways and causing coughing, helping to avoid inhaling any nasty stuff. But in fact they found the opposite – bitter chemicals caused a massive spike in calcium within the muscle cells, making them relax, and making airways become more open. And this isn't just a small effect – it was three times larger than the effect they saw with chemicals called beta-adrenergic receptor agonists – molecules that are commonly used to relieve the airway constriction caused by asthma and other lung diseases.
The scientists think that stimulating these bitter receptors could be a powerful way to treat asthma or other diseases such as chronic obstructive pulmonary disease, or COPD. There are thousands of naturally-produced and man-made bitter chemicals in the world, so at least one – and probably more – might turn out to be suitable as a drug. And the lab research suggests that combining bitter receptor activators with current asthma treatments - such as the beta-adrenergic receptor agonists I mentioned earlier - might pack even more of a punch, as the drugs work in different ways on the lungs. But it might mean that your asthma inhaler tastes pretty nasty!