Do Acids get on Your Nerves?

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Gerard Lairesse’s rendering of Cleopatra’s Banquet.

Egypt, Circa 30 B.C.

Cleopatra and Mark Anthony were discussing their love for each other. Anthony was certain he loved Cleopatra more than she loved him. After all he had left his wife and country behind for her. But the last queen of Egypt was not about to give up so easily. After two forced incestuous marriages, she had found love. So she made a wager that she will arrange a single meal worth 10000000 sesterces ($ 30 million) for Anthony. The Roman nobleman accepted the bet, surely Cleopatra was bluffing right? Wrong. Next day, an exquisite and enormous meal was arranged in the honor of Anthony but it was not worth anywhere near the promised amount. Just when Anthony thought he had won the bet, the servants brought a toast glass full of vinegar and put it in front of Cleopatra. She took off one of her pearl earrings, made of the biggest pearl in the history of the world, dissolved it in the glass full of vinegar and drank to the health of her beloved. The legend goes, she was about to dissolve her other earring also, when the referee of the bet interjected that the meal is already worth more than 10000000 sesterces. (The most expensive bottle of champagne I could find on the internet costs a little over 1 million per bottle…)

Besides being the tale of extravagant love, the story tells us that ancient Egyptians had an understanding of acids and bases. The glass full of vinegar was a concentrated solution of acetic acid, which if drank straight up would have killed Cleopatra. However, dissolving the pearl (made of Calcium carbonate) neutralized the acid and made it suitable to drink. It was important to know about acids because acidic and basic balance in our body is highly regulated. Any disruption of that balance causes pain, inflammation or death. But how do our body sense the change in acid levels?

Cut to 1981 when Dr. Oleg Krishtal of Bogomoletz Institute of Physiology, Ukraine discovered the acid sensing ion channels or ASICs. These are proton (hydrogen ion) receptors found mainly in the neurons of dorsal root ganglion in the spinal cord and brain regions like amygdala, cerebellum and cerebral cortex. As all receptors, these are pores made up of proteins that are located in the cell membrane. In the cell membrane ASICS look like closed fists that can sense the level of acidity (by sensing amount of protons) near the cell. Before the discovery of ASICs, physiologists struggled to find the reason as to why during any injury the injured and inflamed site became acidic? Now they found an answer, these ASIC channels were sensing the change in acidity and helping in pain signaling. Indeed, mice reared without this channel experienced less pain during any injury. This has opened up a whole new field of pain therapeutics – from migraine to arthritic pain, a lot of which is still left unexplored. There was another surprising finding in these no ASIC mice, they seemed to have impaired learning ability. This suggests that at least in the hippocampus (the seat of memory in the brain) ASICs play a role in transferring information across two neurons.

Acids indeed remain mystical – from a witness of seductive love to a harbinger of new biomedical frontiers.

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