Japanese researchers have discovered that people feel the sour taste only when the saliva in the mouth washes out an acidic item off the tongue. Professor Makoto Tominaga and Research Assistant Professor Hitoshi Inada of the National Institute for Physiological Sciences at Okazaki have revealed that the receptor, PKD1L3-PKD2L1 channel complex, is key to sour taste feeling.
The researchers say that this receptor can be activated by an acid stimulus, but it produces the sour taste only after the removal of the stimulus.
Reporting their finding in the journal EMBO reports, they called such type of response as "off-response" of sour taste receptor.
During a study, the researchers investigated the PKD1L3-PKD2L1 channel activity stimulated by acid stimulus with calcium imaging method and electrophysiology.
The cultured cells expressing PKD1L3-PKD2L1 channels showed a significant increase in intracellular Ca2+ not during the acid stimulation, but only after the acid stimulus was washed out.
According to the researchers, the off-response property was also confirmed by whole cell patch-clamp configuration.
"The PKD1L3-PKD2L1 channels exist on the taste bud in the side and the inner part of tongue, where the salivary glands are close. Acidic things such as spoiled foods and harmful solutions are supposed to be dangerous to human body so that they should be quickly removed by saliva. The off-response of PKD1L3-PKD2L1 channels, we found here, helps human to keep sour taste sensation even after acid stimulus has been washed out," Prof. Tominaga and Dr. Inada said.