Lecture 1 : the mammalian taste system - Difference between classic taste receptors and channel o Classic · Sweet, umami, bitter . These are GPCR o Salty, sourness o Bitter · X GPCR, these are transmembrane channels · 25 receptors o Calcium Taste sensory cells - 3 types of taste sensory cells o Type 1 : X taste cells . Support cell o Type 2 : EXAM " True sensory cells · Expressing the GPCRs " The taste receptors that are sent through GPCR · 3 taste types · Sweet · Umami · Bitter Classically are the taste sensory cells o Type 3 : . Sour taste - Sub types Taste transduction cascade - Allows us to identify taste sensory cell outside the oral cavity o Use these genes as biomarkers - Stimulation of the taste receptors will engage gustducin o Gustducin · Primer composed of 3 · Alpha · Beta · Gamma · Intracellular already · Activation of the alpha subunit of gustducin
. Will convert PLC will activate PLCB2 into DAG and IP3 o IP3 Fundamental in stimulating receptor in ER that liberates calcium store . Calcium is fundamental for the activation of cells Now release of calcium -> end up depolarising and sending signal to brain . Calcium will activate sodium channel 3.5 which then that leads to depolarising " So voltage dependent sodium channels get further activated with more sodium coming in . And that burst of AP will then change the confirmation of ATP channel, Who is who in the taste sensory cells : EXAM - Taste receptor for bitterness: T2R - Taste receptor for sweetness and umami: X co expressed T1R2 (sweet) and tlr3 (umami) : X overlap o So type 2 cells but need to focus on subtypes for non- bitterness " Tells us that the transient receptor potential, calmodulin is expressed every taste sensory receptor · Essential taste transduction · Different gene expressions for different taste types
Lecture 2 - GPCR driven taste mainly 4 o Sweet o Umami o Fatty acid o Bitter taste - Sour and salty : not driven by GPCR o Transmembrane channel 5 main taste types ENaC Epithelial Na channel CLASS C T1Rs, CaSR, amino acids receptors CLASS B Orthosteric agonist/antagonist OTOPETRIN-1 (OTOP1) Proton channel CLASS A T2Rs, ORs, Fatty acids receptors. M2 (Muscarinic). 90 7 Allosteric agonist/antagonist GTPase domain of the G, a-subunit & y-subunit B-subunit Epithelial Na channel - Salty taste - X GPCR o Transmembrane channel " Letting ions go through directly the intracellular domain · Ex · Decreasing pH -> cause the sense of sourness through type 3 taste sensory cells · Epithelial Na channel o Through the flow of Na ions that will activate that cell and give the sensation of salt o High salt -> bitter taste receptor activation as well GPCR · Need intracellular G protein · 2 different classes for taste · Class A