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It?s Not the Taste Buds
http://www.fiery-foods.com/dave/quest.html
By Dave DeWitt

I admit it, I was completely wrong. But I have an excuse: I was misled by 
published articles. For years I have written that the sensitivity in the 
mouth for capsaicin was controlled by the number of taste buds, and that 
super-tasters, people with a higher concentration of taste buds, couldn?t 
take the hot stuff as well as the non-tasters, who had a genetically-linked 
lesser number of them in their mouths. Sometime in 2002, I received an email 
from a reader telling me I was wrong and that taste buds could only detect 
sour, sweet, bitter, salty, and umami flavors. (Umami is the flavor of 
monosodium glutamate, or MSG.) He wrote that capsaicin is not detected by the 
taste buds because it does not fall into any of those five categories. This 
person promised to forward links to prove me wrong, but he never did, so I 
forgot about it.

Taste Buds Illustration by Lois Lyles

But in May, 2003, the proof was, well, in the spicy pudding. Scientists 
Elizabeth D. Prescott and David Julius of the University of California, San 
Francisco, announced they had identified a lipid molecule called PIP2 that 
plays a crucial role in controlling the strength of the burning sensation 
caused by capsaicin. A lipid molecule is a fatty molecule, insoluble in 
water, but soluble in fat solvents and alcohol?just like capsaicin. In the 
mouth, there is a capsaicin receptor called TRPV1 and the lipid molecule PIP2 
is bound to it. In the presence of capsaicin, the PIP2 molecule separates 
from the receptor, causing a painful sensation. Here?s the scientific 
description: "In this process, the capsaicin receptor (TRPV1) is sensitized 
by phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis following 
phospholipase C activation." That?s quite a mouthful.

Now, what governs the degree of pain? The strength of the binding of the 
molecule to the receptor, say the scientists?the stronger the binding, the 
more powerful the pain sensation when the capsaicin causes the separation. 
And what determines the strength of the binding? To quote the researchers: 
"Thus, modification of this PIP2 regulatory domain by genetic, biochemical, 
or pharmacological mechanisms may have profound effects on sensitivity of 
primary afferent nerve fibers to chemical and thermal stimuli under normal or 
pathological conditions."

Now I?m no scientist, but it seems to me that they are saying that the 
sensitivity to capsaicin is determined by genetics?some people?s lipid 
molecules have a stronger bond with the capsaicin receptors than others. But 
by stating that biochemical and pharmacological mechanisms can also play a 
role, this could explain why some people become desensitized to capsaicin and 
can take more and more heat.

I?m certain that further study will reveal even more information regarding 
this process, so stay tuned. And by the way, if you are worried about 
capsaicin destroying your five to ten thousand taste buds, you should know 
that all of them are replaced every two weeks, anyway. So forget about your 
taste buds and concentrate on the binding of your lipid molecules!