Hot or cold? Debate on protein heats up.The pungency of wasabi, horseradish horseradish Hardy perennial plant (Armoracia lapathifolia) of the mustard family, native to Mediterranean lands and grown throughout the temperate zones. Its hotly pungent, fleshy root is used as a condiment and is traditionally considered medicinal. , brussels sprouts Brussels sprouts, variety (gemmifera) of cabbage producing small edible heads (sprouts) along the stem. It is cultivated like cabbage and was first developed in Belgium and France in the 18th cent. , and mustards comes from compounds called isothiocyanates. Applying those same compounds to a person's skin can cause pain and inflammation. Isothiocyanates activate pain-signaling neurons by triggering a cell-surface protein that lets ions into cells, David Julius of University of California, San Francisco and his colleagues report in an upcoming Nature. Julius' group had previously shown that capsaicin capsaicin /cap·sa·i·cin/ (kap-sa´i-sin) an alkaloid irritating to the skin and mucous membranes, the active ingredient of capsicum; used as a topical counterirritant and analgesic. cap·sa·i·cin n. , the compound that gives chili peppers their spicy kick, activates a different but related ion channel ion channel n. See channel. (SN: 11/8/97, p. 297). Curiously, the active ingredient in marijuana triggers the same ion channel that the isothiocyanates do, the researchers found. In another twist, Julius and his colleagues tried but failed to confirm another group's claim that this protein also enables some nerve cells to respond to painfully cold temperatures (SN: 5/10/03, p. 301). "We don't really know why our results differ," Julius says. Studies of sensory nerves from mice genetically engineered to lack the protein may resolve its roles, he adds.--J.T. |
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