Tastant receptors

There are some hundred different 7TM receptors involved in perception of bitter tastants. The bitter taste receptors also couple through the G protein gustducin yielding the activated Gag-GTP which can thence activate C.AMP/C.GMP phosphodiesterase, thus lowering cAMP and cGMP concentration. Bitter tastant receptors can also act via pertussis... 

Here are the bare essentials of taste bud structure. At the top of the taste bud, there is a small pore opening into the bud. Tastants get access to the taste bud molecular machinery through this pore. The body of the taste bud is composed of 30-100 individual neuroepithelial cells, of three types. The key cell type is the sensory cell in whose membrane is embedded the receptors for tastants. The afferent taste nerve... 

Taste bud a structure in the mouth housing receptors for tastants. 

After the saliva has carried the tastants into the taste bud, they interact with the taste receptors on the surface of the cells, or with ion channels, which are pore-like proteins. Salty and sour tastants act through ion channels, and sweet and bitter sensations are mediated by surface receptors. The different taste submodalities rely on specific mechanisms Na+ flux through Na+... 

An important goal toward understanding sensation at the molecular level is the characterization of receptor proteins which bind a specific odorant or tastant Two approaches have been taken direct binding studies of stimulant with a receptor preparation, and identification of genes that code for receptor proteins. The weak reversible interactions make it difficult to stabilize such a complex for isolation and... 

Gustatory neurons have serpentine receptors that respond to tastants by altering [cAMP], which in turn changes Vm by gating ion channels. 

Abietane diterpenes (C61C61C6 with varying degrees of unsaturation) include the 5-LOX inhibitor abietane, the GABA(A) receptor antagonist taxodione and the bitter tastant carnosol. 

Floriano WB, Hall S, Vaidehi N, Kim U, Drayna D, Goddard WA 3rd. Modeling the human PTC bitter-taste receptor interactions with bitter tastants. J. Mol. Model. 2006 12 931-941. 

Tastants are detected by specialized structures called taste buds, which contain approximately 150 cells, including sensory neurons Figure 32.12). Fingerlike projections called microvilli, which are rich in taste receptors, project from one end of each sensory neuron to the surface of the tongue. Nerve fibers at the opposite end of each neuron carry electrical impulses to the brain in response to stimultation by tastants. Structures called taste papillae contain numerous taste buds. 

Importantly, each taste receptor cell expresses many different members of the T2R family. This pattern of expression stands in sharp contrast to the pattern of one receptor type per cell that characterizes the olfactory system (Figure 32.16). The difference in expression patterns accounts for the much greater specificity of our perceptions of smells compared with tastes. We are able to distinguish among subtly different odors because each odorant stimulates a unique pattern of neurons. In contrast, many tastants stimulate the same neurons. Thus, we perceive only "bitter" without the ability to discriminate cycloheximide from quinine. 

Salty tastants are not detected by 7TM receptors. Rather, they are detected directly by their passage through ion channels expressed on the surface of cells in the tongue. Evidence for the role of these ion channels comes from examining known properties of sodium channels characterized in other biological contexts. One class of channels, characterized first for their role in salt reabsorption, are thought to be important in salt taste detection because they are sensitive to the compound amiloride, which mutes the taste of salt and significantly lowers sensory neuron activation in response to sodium. 

Spadaccini R, Trabucco F, Saviano G, Picone D, Crescenzi O, Tancredi T, Temussi PA (2003) The mechanism of interaction of sweet proteins with the T1R2-T1R3 receptor evidence from the solution structure of G16A-MNEI. J Mol Biol 328 683-692 Spillane WJ, Kelly DP, Curran PJ, Feeney BG (2006) Structure-taste relationships for disubsti-tuted phenylsulfamate tastants using classification and regression tree (CART) analysis. J Agric Food Chem 54 5996-6004... 

A central question in bitter taste research is if bitter taste receptor cells are broadly tuned sensors for most, if not all, bitter tastants, or if bitter taste receptor cells are rather heterogeneous, thus providing a potential cellular basis for a discrimination... 

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