托福阅读材料：人的味觉系统

　　托福考试阅读材料：

　　Take a deep breath. Taste anything? Actually， your lungs may. Because scientists have discovered that the same receptors that exist on the tongue to taste bitter substances are also found on the smooth muscle of the lungs.

　　Researchers were studying the receptors on smooth lung muscles that regulate contraction and relaxation of theairways. That’s when they made the discovery—which was so unexpected that the researchers themselves were skeptical.

　　Finally， they became convinced that the receptors were really there， though not clustered in taste buds as they are on the tongue. The scientists then exposed human and mouse airways to various bitter compounds to gauge the effects.

　　Many toxic compounds are bitter， so the researchers expected the lung muscle to tense up and contract—to compel the breather to move away from whatever was bitter and perhaps toxic. But， in a second surprise， bitter compounds relaxed and opened airways better than any existing asthma drug. The study is in the journal Nature Medicine. [Deepak Deshpande et al.， “Bitter taste receptors on airway smooth muscle bronchodilate by localized calcium signaling and reverse obstruction”]

　　Researchers will continue to search for the role of the receptors. Meanwhile， the work represents a surprising new lead in the search for drugs to treat asthma， emphysema or chronic bronchitis.

　　—Cynthia Graber