According to a new study published online in the journal BMC Neuroscience, taste receptors of felines respond in a unique way to bitter compounds compared with humans.

The ability to detect bitter chemicals is thought to have evolved because of its utility in avoiding toxic compounds often found in plants.

All cats, from pets to wild tigers, are carnivores that consume little plant material. Domestic cats, however, may still encounter bitter flavors in food and medicines.

“Feline bitter taste has not been well studied. We applied our experience in studying membrane proteins, such as taste receptors, to enable this first glimpse into how domestic cats perceive bitterness in food at a molecular level,” said Dr Joseph Rucker from Integral Molecular Inc. in Philadelphia, PA, a co-author on the study.

Dr Rucker and his colleagues studied the behavior of two different cat bitter taste receptors – Tas2r38 and Tas2r43 – in cell-based experiments, investigating their responsiveness to bitter compounds, and comparing these to the human versions of these receptors.

“We were surprised to see that one of the cat taste receptors responded to a more limited range of bitter compounds compared to humans, suggesting that cats may be detecting a narrower, or at least a different, repertoire of bitter-tasting compounds,” Dr Rucker said.

TAS2R38 is a bitter taste receptor in humans of which some people have ‘supertaster’ variants that give them an extreme sensitivity to bitter compounds, explaining some people’s strong aversions to broccoli and Brussels sprouts.

Compared with the human TAS2R38 receptor, the cat version was tenfold less sensitive to a key bitter compound PTC and did not respond at all to another bitter compound PROP.

Like its human counterpart, the cat bitter taste receptor Tas2r43 was activated by bitter compounds aloin (found in the aloe plant) and denatonium (used to deter children and pets from consuming chemicals such as antifreeze) but responded differently to the compounds.

The cat receptor was less sensitive to aloin and more sensitive to denatonium than the human receptor.

It also differed from the human taste receptor by being insensitive to saccharin, an artificial sweetener that tends to have a bitter aftertaste in humans.

“We confront the challenge of ‘finicky cats’ every day. As such, it is exciting to find an unexpected receptor response to bitter compounds that has never been described in the literature to date for any other species,” said study co-author Dr Nancy Rawson of AFB International in St. Charles, MO.

“These insights and future discoveries will be invaluable in formulating appealing food for cats, as well as enhancing the acceptability of their medications.”

The scientists also found that probenecid, a known inhibitor of human bitter taste receptors, also worked on both cat taste receptors, preventing stimulation when in the presence of PTC, aloin and denatonium.

According to the team, these insights and further study could be instrumental in formulating appetizing food for household cats as well as designing masking agents to enhance the acceptability of medications.

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Michelle M Sandau et al. 2015. A functional comparison of the domestic cat bitter receptors Tas2r38 and Tas2r43 with their human orthologs. BMC Neuroscience 16: 33; doi: 10.1186/s12868-015-0170-6