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

Abstract

1Taste receptor cells use multiple signaling pathways to detect chemicals in 2 potential food items. These cells are functionally grouped into different types: Type I 3 cells act as support cells and have glial-like properties; Type II cells detect bitter, sweet, 4 and umami taste stimuli; and Type III cells detect sour and salty stimuli. We have 5 identified a new population of taste cells that are broadly tuned to multiple taste stimuli 6 including bitter, sweet, sour and umami. The goal of this study was to characterize 7 these broadly tuned (BR) taste cells. We used an IP3R3-KO mouse (does not release 8 calcium (Ca 2+ ) from Type II cells when stimulated with bitter, sweet or umami stimuli) to 9 characterize the BR cells without any potentially confounding input from Type II cells.

First evidence for the presence of amino acid sensing mechanisms in the fish gastrointestinal tract

“…In mammals, while the PLCβ2-mediated pathway is the most widely accepted signal transduction pathway involved in sweet, bitter, and umami taste detection in taste bud cells, it has been demonstrated that other alternative pathways independent of PLCβ2 and TRPM5 are also activated in response to these compounds. This evidence is based on genetic studies showing that the deletion of signaling proteins, including PLCβ2, ITPR3 and TRPM5, diminishes but does not completely abolish the detection of all bitter, sweet and umami stimuli 44 , 49 – 52 . Among the alternative signaling molecules described so far as being involved in taste transduction are PLCβ3 49 , 53 and inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) 53 .…”

“…This evidence is based on genetic studies showing that the deletion of signaling proteins, including PLCβ2, ITPR3 and TRPM5, diminishes but does not completely abolish the detection of all bitter, sweet and umami stimuli 44 , 49 – 52 . Among the alternative signaling molecules described so far as being involved in taste transduction are PLCβ3 49 , 53 and inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) 53 . Present results showing the activation of plcb3 and plcb4 mRNAs in the rainbow trout GIT in response to the luminal presence of amino acids are in accordance with these observations in mammals, and point towards PLCβ3 and 4 being the main PLC subtypes involved in taste transduction pathways in the gut of this species.…”

First evidence for the presence of amino acid sensing mechanisms in the fish gastrointestinal tract

“…In mammals, while the PLCβ2-mediated pathway is the most widely accepted signal transduction pathway involved in sweet, bitter, and umami taste detection in taste bud cells, it has been demonstrated that other alternative pathways independent of PLCβ2 and TRPM5 are also activated in response to these compounds. This evidence is based on genetic studies showing that the deletion of signaling proteins, including PLCβ2, ITPR3 and TRPM5, diminishes but does not completely abolish the detection of all bitter, sweet and umami stimuli 44 , 49 – 52 . Among the alternative signaling molecules described so far as being involved in taste transduction are PLCβ3 49 , 53 and inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) 53 .…”

“…This evidence is based on genetic studies showing that the deletion of signaling proteins, including PLCβ2, ITPR3 and TRPM5, diminishes but does not completely abolish the detection of all bitter, sweet and umami stimuli 44 , 49 – 52 . Among the alternative signaling molecules described so far as being involved in taste transduction are PLCβ3 49 , 53 and inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) 53 . Present results showing the activation of plcb3 and plcb4 mRNAs in the rainbow trout GIT in response to the luminal presence of amino acids are in accordance with these observations in mammals, and point towards PLCβ3 and 4 being the main PLC subtypes involved in taste transduction pathways in the gut of this species.…”

Bitter taste receptors

“…Recent research also postulates the existence of a broadly tuned subset of Type III cells using a PLCβ3 signaling pathway to respond to umami, sweet, and bitter stimuli ( Banik et al 2020 ). Another kind of cell found in taste buds is the Type IV cells.…”

Critically evaluating sweet taste receptor expression and signaling through a molecular pharmacology lens

“…Upon ligand binding, heterotrimeric G proteins consisting of an a (green), b (blue) and c (pink) subunit are activated by the TAS1R2 subunit of the STR. [41,42]. However, this is still an indirect measure.…”

First evidence for the presence of amino acid sensing mechanisms in the fish gastrointestinal tract

“…In mammals, while the PLCβ2-mediated pathway is the most widely accepted signal transduction pathway involved in sweet, bitter, and umami taste detection in taste bud cells, it has been demonstrated that other alternative pathways independent of PLCβ2 and TRPM5 are also activated in response to these compounds. This evidence is based on genetic studies showing that the deletion of signaling proteins, including PLCβ2, ITPR3 and TRPM5, diminishes but does not completely abolish the detection of all bitter, sweet and umami stimuli 44 , 49 – 52 . Among the alternative signaling molecules described so far as being involved in taste transduction are PLCβ3 49 , 53 and inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) 53 .…”

“…This evidence is based on genetic studies showing that the deletion of signaling proteins, including PLCβ2, ITPR3 and TRPM5, diminishes but does not completely abolish the detection of all bitter, sweet and umami stimuli 44 , 49 – 52 . Among the alternative signaling molecules described so far as being involved in taste transduction are PLCβ3 49 , 53 and inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) 53 . Present results showing the activation of plcb3 and plcb4 mRNAs in the rainbow trout GIT in response to the luminal presence of amino acids are in accordance with these observations in mammals, and point towards PLCβ3 and 4 being the main PLC subtypes involved in taste transduction pathways in the gut of this species.…”

Bitter taste receptors

“…Recent research also postulates the existence of a broadly tuned subset of Type III cells using a PLCβ3 signaling pathway to respond to umami, sweet, and bitter stimuli ( Banik et al 2020 ). Another kind of cell found in taste buds is the Type IV cells.…”

Critically evaluating sweet taste receptor expression and signaling through a molecular pharmacology lens

“…Upon ligand binding, heterotrimeric G proteins consisting of an a (green), b (blue) and c (pink) subunit are activated by the TAS1R2 subunit of the STR. [41,42]. However, this is still an indirect measure.…”

First evidence for the presence of amino acid sensing mechanisms in the fish gastrointestinal tract

“…In mammals, while the PLCβ2-mediated pathway is the most widely accepted signal transduction pathway involved in sweet, bitter, and umami taste detection in taste bud cells, it has been demonstrated that other alternative pathways independent of PLCβ2 and TRPM5 are also activated in response to these compounds. This evidence is based on genetic studies showing that the deletion of signaling proteins, including PLCβ2, ITPR3 and TRPM5, diminishes but does not completely abolish the detection of all bitter, sweet and umami stimuli 44 , 49 – 52 . Among the alternative signaling molecules described so far as being involved in taste transduction are PLCβ3 49 , 53 and inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) 53 .…”

“…This evidence is based on genetic studies showing that the deletion of signaling proteins, including PLCβ2, ITPR3 and TRPM5, diminishes but does not completely abolish the detection of all bitter, sweet and umami stimuli 44 , 49 – 52 . Among the alternative signaling molecules described so far as being involved in taste transduction are PLCβ3 49 , 53 and inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) 53 . Present results showing the activation of plcb3 and plcb4 mRNAs in the rainbow trout GIT in response to the luminal presence of amino acids are in accordance with these observations in mammals, and point towards PLCβ3 and 4 being the main PLC subtypes involved in taste transduction pathways in the gut of this species.…”

Bitter taste receptors

“…Recent research also postulates the existence of a broadly tuned subset of Type III cells using a PLCβ3 signaling pathway to respond to umami, sweet, and bitter stimuli ( Banik et al 2020 ). Another kind of cell found in taste buds is the Type IV cells.…”

Critically evaluating sweet taste receptor expression and signaling through a molecular pharmacology lens

“…Upon ligand binding, heterotrimeric G proteins consisting of an a (green), b (blue) and c (pink) subunit are activated by the TAS1R2 subunit of the STR. [41,42]. However, this is still an indirect measure.…”