Decrease in rat taste receptor cell intracellular pH is the proximate stimulus in sour taste transduction

Abstract

Taste receptor cells (TRCs) respond to acid stimulation, initiating perception of sour taste. Paradoxically, the pH of weak acidic stimuli correlates poorly with the perception of their sourness. A fundamental issue surrounding sour taste reception is the identity of the sour stimulus. We tested the hypothesis that acids induce sour taste perception by penetrating plasma membranes as H(+) ions or as undissociated molecules and decreasing the intracellular pH (pH(i)) of TRCs. Our data suggest that taste nerve responses to weak acids (acetic acid and CO(2)) are independent of stimulus pH but strongly correlate with the intracellular acidification of polarized TRCs. Taste nerve responses to CO(2) were voltage sensitive and were blocked with MK-417, a specific blocker of carbonic anhydrase. Strong acids (HCl) decrease pH(i) in a subset of TRCs that contain a pathway for H(+) entry. Both the apical membrane and the paracellular shunt pathway restrict H(+) entry such that a large decrease in apical pH is translated into a relatively small change in TRC pH(i) within the physiological range. We conclude that a decrease in TRC pH(i) is the proximate stimulus in rat sour taste transduction.

Hydrocolloid sour taste control in pasteurized rice

“…Previous psychophysical and animal physiological studies reported that for a given pH, the sour gustatory stimuli of weak acids like acetic and citric acids were similarly found to be more sour than stronger acids (Ugawa et al 1998;Ogiso et al 2000;Lyall et al 2001;Richter et al 2003;Lugaz et al 2005). Weak acids tend to acidify taste cells of the tongue to a greater extent than stronger acids .…”

Temperature Influences Chorda Tympani Nerve Responses to Sweet, Salty, Sour, Umami, and Bitter Stimuli in Mice

“…We chose to examine the influence of temperature on an equimolar concentration (0.05 M) of HCl, citric acid, and acetic acid, as these acids are effective sour stimuli at these concentrations at our temperature range (Horio et al 2011), but are quite different from another in terms of solution pH (HCl = 1.3, citric acid = 2.24, and acetic acid = 3.03). Importantly, acid responses from the rat CT neurons are not directly correlated to solution pH, because weak acids are more effective stimuli than their pH would suggest (Lyall et al 2001;Breza and Contreras 2012a). A decrease in the intracellular pH appears to be the proximate stimulus in sour taste transduction (Lyall et al 2001), but weak acids, such as acetic acid and carbonic acid, are more effective (at the same solution pH) at decreasing intracellular pH than HCl, a strong mineral acid (Lyall et al 2001).…”

“…Importantly, acid responses from the rat CT neurons are not directly correlated to solution pH, because weak acids are more effective stimuli than their pH would suggest (Lyall et al 2001;Breza and Contreras 2012a). A decrease in the intracellular pH appears to be the proximate stimulus in sour taste transduction (Lyall et al 2001), but weak acids, such as acetic acid and carbonic acid, are more effective (at the same solution pH) at decreasing intracellular pH than HCl, a strong mineral acid (Lyall et al 2001).…”

“…This may imply that the effects of temperature may have intracellular and extracellular sites of action or multiple receptor mechanisms, and warrants future investigation. It could also imply that the mechanisms of sour-taste transduction in rats and mice differ, since responses to acids in whole nerve and single cell recordings (Lyall et al 2001;Breza and Contreras 2012a) of rats are similar when matched for concentrations, despite differences in solution pH.…”

The sour taste of a proton current

“…In their protonated, electrically neutral form, the weak acids can cross the plasma membrane and enter taste cells, where they acidify the cytosol. Indeed, such induced cytosolic acidification is believed to contribute directly to the sour taste of weak acids (11,12).…”