Human Skin Can Taste Things, And Scientists Just Figured Out Why
Ever set off too many of the bitter taste receptors on your tongue? You probably spat out whatever it was in your mouth, and that's our best guess for why we even have them: to stop us from ingesting things that might be harmful.
Our skin cells have the same receptors, which serve a similar purpose on a cellular level: to detect bitter substances. New research led by Okayama University of Science biologists builds on our knowledge of the type-2 taste receptors (TAS2Rs) found in the skin's keratinocytes, finding their role is also to keep potentially harmful materials from sticking around and causing damage.
Once thought to be confined to the tongue, TAS2Rs are actually spread much further throughout the body. They line your colon, your stomach, and your upper airways.
A 2015 paper discovered them not just lurking but bristling with activity in the keratinized epithelial cells of human skin. The new research gets into the question of what exactly they are doing there.
Lab-grown human keratinocytes were fed the quintessential 'bitter pill,' phenylthiocarbamide (PTC), which has been used in all sorts of studies around the genetics of bitter taste.
On detecting and binding with the PTC, the receptors triggered production of a fleet of ABC transporters to shuttle the bitter compound across the membranes and back out of the cell.
To determine whether this newly-installed exit was functional, the team administered a visible tracer dye which could be rapidly excreted from the cell via a specific ABC transporter. When the team treated the cells with a substance called verapmil which is known to inhibit the transporter, the tracer had no way out, allowing it to accumulate.
The researchers think this chain of events set off by the TAS2Rs protects the cell from being damaged by potentially toxic bitter compounds, a premise that runs in line with theories about why we can taste 'bitter' at all.
When it comes to taste on the tongue, the jury is still out on whether bitterness actually helps us detect harmful substances. Studies have found this flavor profile may not be such a helpful indicator of toxicity as we once thought, with many popular foods and drinks featuring a bitter flavour profile, and many toxic substances lacking it.
But this latest study shows that among skin cells, at least, the receptors might have some benefit in surviving exposure to toxins. Cells that were given a toxic level of antihistamine had much better survival rates when their bitter receptors had been fired up prior.
"Activation of TAS2Rs by bitter compounds, such as PTC and saccharin, enhances ABCB1 production, leading to the prevention of diphenhydramin-induced cell death via excretion of these compounds," the authors report.
Verapamil also reversed this protective effect.
"Altogether, harmless activators of TAS2Rs may be promising drugs that enhance the excretion of toxic substances from the human skin," the authors suggest.
Coffee scrub, anyone?
This research was published in FASEB BioAdvances.
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