I just read that most humans can taste CO2 - study put the subjects into a hyperbaric chamber and fed them flat coke and coke that did not fizz but was carbonated; everyone seemed to taste the fizz and were able to tell them apart.
Interesting observation: humans use CO2 to determine there is enough air to breath. I wonder if these are 2 separate genetic paths or does on piggyback on the other.
You taste the carbonation because CO2 dissolved in water creates carbonic acid, which gives the drink a slightly tart flavor. I doubt it has anything to do with breathing.
Acetazolamide, a carbonic anhydrase inhibitor used for (among other things) treating altitude sickness, affects the way the human body processes carbon dioxide. Without digging into how it works, it helps you adjust to lower partial pressure of CO[sub]2[/sub] due to increased respiration at high altitudes, or at least keeps it from screwing up the pH of your blood.
People taking acetazolamide generally find carbonated drinks unpleasant while under the effects of the medication. This ranges from reporting that they taste “flat” to my own somewhat colorful description of the drinks as tasting like demon bile. It’s possible the variation in responses is related to different levels of sensitivity to bitter flavors, but as far as I know, everyone experiences the effect to some degree. This study suggests that the sensation we associate with carbonated drinks is chemogenic, and affected by acetazolamide, while other acidic flavorings are not.
I suspect that supports a link, if not interdependence, between CO[sub]2[/sub] in a respiratory context and in the ability to taste/feel it in drinks.
Acidic liquids in general have a generally sour flavor.
Acid solutions consist of some hydrogen-containing ionic compound dissolved in water, in which the hydrogen ions separate from the rest of the molecule into the solution. So you have a soup of water and free-floating hydrogen ions, plus the other parts of those molecules. It’s those loose hydrogen ions that give acids all the properties commonly associated with acids: Sour taste and ability to dissolve other stuff.
I’m a bit curious about what the Aceta… reads back… zolamide does, or what in particular it treats.
I’m a diver and in a few occasions I had splitting migraines after a dive from, most probably, CO2 buildup.
I wonder if that drug or something similar, could be used to help with that, because Paracetamol had more or less the same effect as taking Tic-Tacs.
Bear in mind that I’m not an expert–I just read up on the stuff when I was taking it for a game at high altitude–but I think it would be counterproductive for a diver, if not actually dangerous. Here are the basics, as I understand them:
CO[sub]2[/sub] dissolved in your blood forms carbonic acid, lowering its pH. Blood pH is tightly regulated, however, and the body has a system for buffering the acid using bicarbonate, which is a base. (It buffers other acids as well, but it’s carbonic we’re concerned with.) At high altitudes, though, you breathe harder and the partial pressure of CO[sub]2[/sub] is lower, so you dump CO[sub]2[/sub] faster and have less in your blood. Until your body adjusts to this, you may have more bicarbonate in your blood than you need.
That’s where the drug comes in–as I said, it’s a carbonic anhydrase inhibitor. Carbonic anhydrases are enzymes that catalyze the conversion of CO[sub]2[/sub] into bicarbonate. Inhibiting them slows down the production of bicarbonate. The inhibitors also have diuretic effects, causing you to dump existing bicarbonate via your kidneys. Adjusting the level of bicarbonate helps you acclimatize to high altitude more quickly and prevents some altitude sickness symptoms in the meantime.
So, basically, acetazolamide is for use when you have too little CO[sub]2[/sub], not too much–the opposite of a diver’s usual situation.
In my experience, it also causes you to breathe harder at your accustomed air pressure. That’s anecdotal, but if it’s true for others, I think that would also be contraindicated for a diver.
On another note, since we’re discussing the chemical details–our sour-sensing taste buds express CA-IV, a carbonic anhydrase enzyme. It could be that it’s present to help maintain pH balance of the taste buds themselves, but I would speculate that it might have developed to help us detect fermentation (and thus, probable spoilage) in food and drink. (It also provides us with the fun factoid that taking a sip of soda makes our mouths synthesize something similar to Alka-Seltzer.)
So, we have a common mechanism, carbonic anhydrase enzymes, involved both in regulating breathing and in tasting CO[sub]2[/sub]. Their functions, however, seem to be highly divergent.
I participated in one of the drug studies - climbed Mt Rainier twice, once with and once w/o. It was difficult to do a double blind study that made all carbonated beverages taste like shit. I had more discomfort on the drug than on the placebo but that was due to the difference in coming down off the mountain w/regular gear and coming down with someone else’s rope - those ropes can drag a man down at the end of a long trek. sigh - all I got out of it was climbing Mt Rainier and a week of bad coke and beer.