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When it comes to food, the world abounds with people who pride themselves on having discriminating taste. Scientific assessments of our gustatory sensibilities, however, have proved less certain of that notion. A study conducted last year, for example, led researchers to conclude that, as far as our taste cells are concerned, all bitter flavors are the same. Now new findings, reported Friday in the journal Science, are calling that theory into question. Our taste buds, the researchers argue, are actually spectacularly sensitive to different bitter compounds.
When a taste receptor detects a bitter stimulus, it induces an increase in calcium concentrations in the cell. This prompts the cell to release a neurotransmitter. So in order to study the effects of different bitter compounds on taste cells, biologists Alejandro Caicedo and Stephen Roper of the University of Miami injected a fluorescent marker of calcium activity into taste cells procured from a rat's tongue. They then exposed the cells to five common bitter compounds, one by one, monitoring the cells' fluorescence levels.
The results were striking. Some 65 percent of the bitter-sensitive cells responded to only a single compound; 26 percent responded to two compounds; and 7 percent responded to more than two compounds. "It appears that different taste cells are tuned to different bitter compounds," Roper told Science. "These cells are not generalists, as some suggest." Although distinctions appear to be made at the cellular level, the authors note that whether or not bitter compounds can be discriminated behaviorally remains to be determined.
