Substances that give some foods their bitter flavor also act to reverse the contraction of airway cells,paving way for treatment of airway obstructive diseases such as asthma,scientists say.
Researchers at the University of Massachusetts Medical found that substances responsible for bitter flavor in foods reverse the contraction of airway cells,a process known as bronchodilation.
This effect may one day be harnessed to provide improved treatments for airway obstructive diseases such as asthma and chronic obstructive pulmonary disease. A hallmark of an asthma attack is excessive contraction of smooth muscle cells,which causes narrowing of the airways and subsequent breathing difficulties.
The fact that bitter substances can relax these smooth muscle cells suggests that they may have the potential to halt asthma attacks and in fact could even be an improvement over current treatments since the relaxation effects are quite fast,researchers said.
“I am excited that someday,with more research,there may be a new class of bronchodilators which are able to reverse an asthma attack quicker and with fewer side effects than is currently available to patients,” said Ronghua ZhuGe,senior author of the study.
However,the mechanisms by which bitter taste receptor activation causes a cell to relax were unknown. To help unravel these mechanisms,ZhuGe and colleagues examined the effect of bitter substances on the contraction of airways and in single isolated cells.
During an asthma attack,channels on the membrane of smooth muscle cells in the airways open. This allows calcium to flow into the cell,causing it to contract. When the cells contract,the airway becomes narrower and makes breathing more difficult.
The team determined that bitter substances act by shutting down these calcium channels,allowing bronchodilation. Bitter taste receptors,like most receptors,span the plasma membrane of the cell. Part of the receptor is outside the cell,able to bind (and hence “sense”) bitter substances outside the cell. When a bitter compound binds to a bitter taste receptor,the receptor releases a G-protein,which then splits into two parts: a G alpha subunit and G beta-gamma dimer.
“It is the G beta-gamma dimer that likely acts to close the calcium channels on the plasma membrane,” said Kevin Fogarty,co-author of the study. “Once the channels are closed,the calcium level returns to normal and the cell relaxes. This ends the asthma attack,” he added. The study was published in the journal PLOS Biology.