| MadSci Network: Chemistry |
Hi Tara! What a hot question! I'm going to answer a slightly more general question - - what makes all types of pepper seem "hot," and how does your body react to that information? Chili peppers contain a molecule called capsaicin -- that's what makes them "hot." Different types of peppers contain varying amounts of capsaicin -- the really spicy orange habanero peppers contain lots of capsaicin, while mild green and red chilis contain less. Capsaicin is a member of the vanilloid class of molecules, which are generally non-polar (greasy). Nerve cells (also known as neurons) in your body have receptor molecules for capsaicin. These receptors are protein channels which sit on the surface of neurons, under the skin. They are known as vanilloid receptor-1 (VR!) channels. When the receptors come in contact with capsaicin, the channels open, allowing positive ions to enter the neuron. This inward electrical current (current = moving ions) causes the neurons to signal to other cells in the body, which eventually interpret the stimulus as "pain" or "irritation." That is, unless you're a fan of spicy food. In that case, your brain interprets the activation of capsaicin-sensing neurons in your mouth as "delicious!". What about capsaicin sensors in the nose? Your brain interprets their activation as an unpleasant sensation. In order to rid your nose of the offending substance, you sneeze. Similarly, if you get pepper in your eyes, tears form to wash away the capsaicin. When capsaicin is rubbed into the skin, it causes an inflammatory response -- local redness, swelling, and some tenderness. Recently, capsaicin cremes have been found useful for treating arthritis and other painful joint problems. It sounds paradoxical to treat pain by rubbing an irritating substance on the painful spot, but the treatment probably works by temporarily inactivating the pain-sensing neurons. Here are some more good references on capsaicin and its receptor: http://chemistry.about.com/science/chemistry/library/weekly/ aa091100a.htm Includes pictures of vanilloids and good links http:// www.ucsf.edu/neurosc/faculty/neuro_julius.html The Julius lab first discovered VR1. This site describes some of VR1's other interesting properties, like the ability to sense heat and pH. Hope this helps! Amanda Kahn amandak@phy.ucsf.edu
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