An international team of researchers has revealed that ATP is the primary neurotransmitter behind our ability to taste three of the five basic tastes. The other two taste types, sour and salt, use different mechanisms to send taste information to the brain, say the US-based researchers.
Until now, the team explained, exactly how cells transmit taste information to the brain was pretty much a mystery. However, the new finding reveals that the calcium homeostasis modulator 1 (CALHM1) protein CALHM1 channel protein - which span a taste bud cell's outer membrane - releases ATP to make a neural taste connection.
Writing in Nature, Professor Kevin Foskett, from the University of Pennsylvania, along with colleagues from the Monell Chemical Senses Center, show that the CALHM1 protein is 'indispensable' for taste perception.
"This is an example of a bona fide ATP ion channel with a clear physiological function," said Foskett. "Now we can connect the molecular dots of sweet and other tastes to the brain."
The team revealed that mice in which CALHM1 proteins are absent have 'severely impaired' perceptions of sweet, bitter and umami compounds; whereas, their recognition of sour and salty tastes remains mostly normal.
Using the CALHM1 knockout mice, team members tested how their taste was affected.
"The mice are very unusual," said Dr Michael Tordoff from Monell. "Control mice, like humans, lick avidly for sucrose and other sweeteners, and avoid bitter compounds."
"However, the mice without CALHM1 treat sweeteners and bitter compounds as if they were water. They can't taste them at all."
In addition, they found that CALHM1 was also required for 'non-traditional' polycose, calcium, and aversive high-salt tastes. This, the authors said, implies a loss of all GPCR-mediated taste signals rather than simply sweet, bitter and umami taste.