Taste second messengers

Taste receptor cells are organized into taste buds 825 Sensory afferents within three cranial nerves innervate the taste buds 826 Information coding of taste is not strictly according to a labeled line 826 Taste cells have multiple types of ion channels 826 Salts and acids are transduced by direct interaction with ion channels 826 Taste cells contain receptors, G proteins and second-messenger-effector enzymes 827... 

Sweet, bitter and umami taste involve receptor-coupled second-messenger pathways that are differentially expressed across the gustatory epithelium 827... 

The salty taste is primarily due to sodium ions acting directly on ion channels. Amiloride specifically blocks sodium channels however, it does not block all responses to salt, in cating more than one mechanism for salty sensation. A different compound, 4-aminopyridine, blocks potassium channels but not sodium. This suggests that receptor proteins and second messengers are not uired, and that these stimuli act directly on ion membrane channels. The physiology of the response of cells to salt has been reviewed (7). 

Bruch, R. C. and Teeter, I. H., Second-messenger signaling mechanisms in olfaction, in Receptor Events and Transduction in Taste and Olfaction, Brand, I. G., Teeter, J. H., Cagan, R., and Kare, M. R., Eds., Marcel Dekker, New York, 1988, 283. 

In taste studies, sucrose is usually taken as a reference standard in the sensory evaluation of sweetness and caffeine is generally used as the reference material for bitterness. However, sour and salty tastants modulate taste-receptor function by direct effect on specific ion channels in the membrane, while sweet and bitter tasting compounds seem to bind to closely located receptors which are coupled to a guanidine-nucleotide binding protein (G-protein). The perception of their tastes proceeds through a transduction mechanism involving G-protein and a second messenger system (Kinnamon, 1988). 

Sour and salty taste responses result from the direct action of hydrogen ions or sodium ions on channels these responses therefore have the potential for very rapid time resolution. Taste responses (bitter and sweet) that are likely to require 7TM receptors and second messengers will exhibit slower time resolution. 

Spielman, A.I., H. Nagai, G. Sunavala, M. Dasso, H. Breer, I. Boekhoff, T. Huque, G. Whithey, J.G. Brand, Rapid kinetics of second messenger production in bitter taste, Amer. J. Cell Physiol., 1996(270) p. 926. 

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