18 HHMI BULLETIN | February 2007 Axel: Matthew Septimus Dulac: Matt Kalinowski roasted coffee and takes it black, with sugar, “There is a reward associated with coffee and beer.” For another, “We like to live on the edge and have new sensory experi-ences.” Of course, individuals vary in their taste for bitter substances, causing some people to steer away from strong ales and to dose their coffee with cream and sugar. Not long after the bitter-receptor discovery, Zuker and Ryba functionally characterized the receptors and cells for sweet and umami tastes; in the fall of 2006, the scientists reported that sour taste is detected by a completely separate popula-tion of taste cells expressing an ion channel protein called PKD2L1. The receptor for salt has still not been found. Zuker concludes that taste coding in the tongue and mouth is conﬁgured with “elegant simplicity.” He writes: “It is now clear that distinct cell types, expressing unique receptors, are tuned to detect each of the ﬁve basic tastes. And while certain areas of the tongue are more sensitive to
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