A subset of broadly responsive Type III taste cells contribute to the detection of bitter, sweet and umami stimuli

Abstract

Taste receptor cells use multiple signaling pathways to detect chemicals in potential food items. These cells are functionally grouped into different types: Type I cells act as support cells and have glial-like properties; Type II cells detect bitter, sweet, and umami taste stimuli; and Type III cells detect sour and salty stimuli. We have identified a new population of taste cells that are broadly tuned to multiple taste stimuli including bitter, sweet, sour, and umami. The goal of this study was to characterize these broadly responsive (BR) taste cells. We used an IP 3 R3-KO mouse (does not release calcium (Ca 2+) from internal stores in Type II cells when stimulated with bitter, sweet, or umami stimuli) to characterize the BR cells without any potentially confounding input from Type II cells. Using live cell Ca 2+ imaging in isolated taste cells from the IP 3 R3-KO mouse, we found that BR cells are a subset of Type III cells that respond to sour stimuli but also use a PLCβ signaling pathway to respond to bitter, sweet, and umami stimuli. Unlike Type II cells, individual BR cells are broadly tuned and respond to multiple stimuli across different taste modalities. Live cell imaging in a PLCβ3-KO mouse confirmed that BR cells use this signaling pathway to respond to bitter, sweet, and umami stimuli. Short term behavioral assays revealed that BR cells make significant contributions to taste driven behaviors and found that loss of either PLCβ3 in BR cells or IP 3 R3 in Type II cells caused similar behavioral deficits to bitter, sweet, and umami stimuli. Analysis of c-Fos activity in the nucleus of the solitary tract (NTS) also demonstrated that functional Type II and BR cells are required for normal stimulus induced expression.

Narrowly and Broadly Tuned Peripheral Gustatory Neurons Cooperate to Encode Three Behaviorally Relevant Stimulus Categories

“…This residual response has been shown to be mediated by TRPM4, such that only the combined deletion of both TRPM4 and TRPM5 results in a complete loss of sensitivity to these stimuli ( Dutta Banik et al, 2018 ). Furthermore, consistent with our findings, TRPM4 is expressed in Type III cells ( Dutta Banik et al, 2018 ), and some Type III cells are broadly tuned ( Tomchik et al, 2007 ) and have been shown to transduce these three stimuli ( Dutta Banik et al, 2020 ; Dutta Banik and Medler, 2023 ). Here we show that in the absence of Type II cells, sucrose responses are significantly reduced while bitter responses are not.…”

“…There was no difference between the two genotypes in responses to NaCl ( U = 5771, n = 144, 90, p = 0.16) or bitter mix ( U = 5687, n = 144, 90, p < 0.12). These two stimuli are likely transduced by a combination of Type II and Type III cells ( Lewandowski et al, 2016 ; Dutta Banik et al, 2020 ).…”

Narrowly and Broadly Tuned Peripheral Gustatory Neurons Cooperate to Encode Three Behaviorally Relevant Stimulus Categories

“…This residual response has been shown to be mediated by TRPM4, such that only the combined deletion of both TRPM4 and TRPM5 results in a complete loss of sensitivity to these stimuli ( Dutta Banik et al, 2018 ). Furthermore, consistent with our findings, TRPM4 is expressed in Type III cells ( Dutta Banik et al, 2018 ), and some Type III cells are broadly tuned ( Tomchik et al, 2007 ) and have been shown to transduce these three stimuli ( Dutta Banik et al, 2020 ; Dutta Banik and Medler, 2023 ). Here we show that in the absence of Type II cells, sucrose responses are significantly reduced while bitter responses are not.…”

“…There was no difference between the two genotypes in responses to NaCl ( U = 5771, n = 144, 90, p = 0.16) or bitter mix ( U = 5687, n = 144, 90, p < 0.12). These two stimuli are likely transduced by a combination of Type II and Type III cells ( Lewandowski et al, 2016 ; Dutta Banik et al, 2020 ).…”

Exogenous oral application of PYY and exendin-4 impacts upon taste-related behavior and taste perception in wild-type mice

“…Since QHCl is not amenable to Fura-2 calcium imaging (it produces a background fluorescence that interferes with cell fluorescence readings), we selected another potent and well-studied bitter compound, denatonium benzoate, to use in these experiments. Previous studies have found that the maximal calcium response to denatonium can be elicited in the low millimolar concentration range (i.e., 1 - 10 mM; Dutta Banik et al, 2020 ; Dutta Banik et al, 2018 ; Dutta Banik and Medler, 2023 ; Huang and Wu, 2018 ; Rodriguez et al, 2021 ; Yoshida et al, 2018 ), and work in our lab has corroborated these findings. We chose to focus on the higher end of the response range to observe the potential suppressive effects of PYY 3-36 under robust stimulation.…”

Physiology of Taste Processing in the Tongue, Gut, and Brain

“…Importantly, the loss of either PLC‐β3 (in BR cells) or IP3R3 (in type II cells) significantly impaired both behavioral responses and rNTS taste evoked activity. As noted by Banik et al (10),…”

Narrowly and Broadly Tuned Peripheral Gustatory Neurons Cooperate to Encode Three Behaviorally Relevant Stimulus Categories

“…This residual response has been shown to be mediated by TRPM4, such that only the combined deletion of both TRPM4 and TRPM5 results in a complete loss of sensitivity to these stimuli ( Dutta Banik et al, 2018 ). Furthermore, consistent with our findings, TRPM4 is expressed in Type III cells ( Dutta Banik et al, 2018 ), and some Type III cells are broadly tuned ( Tomchik et al, 2007 ) and have been shown to transduce these three stimuli ( Dutta Banik et al, 2020 ; Dutta Banik and Medler, 2023 ). Here we show that in the absence of Type II cells, sucrose responses are significantly reduced while bitter responses are not.…”

“…There was no difference between the two genotypes in responses to NaCl ( U = 5771, n = 144, 90, p = 0.16) or bitter mix ( U = 5687, n = 144, 90, p < 0.12). These two stimuli are likely transduced by a combination of Type II and Type III cells ( Lewandowski et al, 2016 ; Dutta Banik et al, 2020 ).…”

Exogenous oral application of PYY and exendin-4 impacts upon taste-related behavior and taste perception in wild-type mice

“…Since QHCl is not amenable to Fura-2 calcium imaging (it produces a background fluorescence that interferes with cell fluorescence readings), we selected another potent and well-studied bitter compound, denatonium benzoate, to use in these experiments. Previous studies have found that the maximal calcium response to denatonium can be elicited in the low millimolar concentration range (i.e., 1 - 10 mM; Dutta Banik et al, 2020 ; Dutta Banik et al, 2018 ; Dutta Banik and Medler, 2023 ; Huang and Wu, 2018 ; Rodriguez et al, 2021 ; Yoshida et al, 2018 ), and work in our lab has corroborated these findings. We chose to focus on the higher end of the response range to observe the potential suppressive effects of PYY 3-36 under robust stimulation.…”

Physiology of Taste Processing in the Tongue, Gut, and Brain

“…Importantly, the loss of either PLC‐β3 (in BR cells) or IP3R3 (in type II cells) significantly impaired both behavioral responses and rNTS taste evoked activity. As noted by Banik et al (10),…”

Narrowly and Broadly Tuned Peripheral Gustatory Neurons Cooperate to Encode Three Behaviorally Relevant Stimulus Categories

“…This residual response has been shown to be mediated by TRPM4, such that only the combined deletion of both TRPM4 and TRPM5 results in a complete loss of sensitivity to these stimuli ( Dutta Banik et al, 2018 ). Furthermore, consistent with our findings, TRPM4 is expressed in Type III cells ( Dutta Banik et al, 2018 ), and some Type III cells are broadly tuned ( Tomchik et al, 2007 ) and have been shown to transduce these three stimuli ( Dutta Banik et al, 2020 ; Dutta Banik and Medler, 2023 ). Here we show that in the absence of Type II cells, sucrose responses are significantly reduced while bitter responses are not.…”

“…There was no difference between the two genotypes in responses to NaCl ( U = 5771, n = 144, 90, p = 0.16) or bitter mix ( U = 5687, n = 144, 90, p < 0.12). These two stimuli are likely transduced by a combination of Type II and Type III cells ( Lewandowski et al, 2016 ; Dutta Banik et al, 2020 ).…”

Exogenous oral application of PYY and exendin-4 impacts upon taste-related behavior and taste perception in wild-type mice

“…Since QHCl is not amenable to Fura-2 calcium imaging (it produces a background fluorescence that interferes with cell fluorescence readings), we selected another potent and well-studied bitter compound, denatonium benzoate, to use in these experiments. Previous studies have found that the maximal calcium response to denatonium can be elicited in the low millimolar concentration range (i.e., 1 - 10 mM; Dutta Banik et al, 2020 ; Dutta Banik et al, 2018 ; Dutta Banik and Medler, 2023 ; Huang and Wu, 2018 ; Rodriguez et al, 2021 ; Yoshida et al, 2018 ), and work in our lab has corroborated these findings. We chose to focus on the higher end of the response range to observe the potential suppressive effects of PYY 3-36 under robust stimulation.…”

Physiology of Taste Processing in the Tongue, Gut, and Brain

“…Importantly, the loss of either PLC‐β3 (in BR cells) or IP3R3 (in type II cells) significantly impaired both behavioral responses and rNTS taste evoked activity. As noted by Banik et al (10),…”