Mechanisms of sensory transduction

Nevertheless, there is good evidence that in all purely bluelight sensitive organisms, the photoreceptor is a flavin (flavoprotein) (Table 2), which appears to be bound to membranes (plasmalemma) in a highly dichroic manner. The mechanism of sensory transduction is probably correlated with light-induced redox reactions mediated by a flavin. This observation is consistent with the fact that nearly all physiolog-... 

Chemosensory neurons of the vomeronasal system are narrowly tuned to specific chemical cues, and utilize a unique mechanism of sensory transduction 824... 

FIGURE 50-6 A model for chemosensory transduction in vomeronasal sensory neurons. The individual steps are detailed in the text. In contrast to the transduction cascade in OSNs, the mechanism of vomeronasal transduction is less well characterized. Vomeronasal neurons express either V1R or V2R receptors and either Got. or Ga0, respectively. The TRPC2 channel subunit is expressed in all vomeronasal neurons, and may be part of a multimeric channel complex. Ca2+ions are represented as purple balls, Na+ ions as blue balls. VR, vomeronasal receptor (VlRorV2R) PIP2, phospha-tidylinositol 4,5-bishphosphate IP, inositol 1,4,5-trisphosphate DAG, diacylglycerol. 

Kimoto H, Haga S, Sato K, Touhara K (2005) Sex-specific peptides from exocrine glands stimulate mouse vomeronasal sensory neurons. Nature 437 898-901 Kinnamon SC, Margolskee RF (1996) Mechanisms of taste transduction. Curr Opin Neurobiol 6 506-513... 

Taste-active chemicals react with receptors on the surface of sensory cells in the papillae causing electrical depolarization, ie, drop in the voltage across the sensory cell membrane. The collection of biochemical events that are involved in this process is called transduction (15,16). Not all the chemical steps involved in transduction are known however, it is clear that different transduction mechanisms are involved in different taste quaUties different transduction mechanisms exist for the same chemical in different species (15). Thus the specificity of chemosensory processes, ie, taste and smell, to different chemicals is caused by differences in the sensory cell membrane, the transduction mechanisms, and the central nervous system (14). 

Scheme 3. Flavins are capable to undergo both 1 e and 2 e input/output redoxreactions as indicated. Since cytochrome b is a typical 1 e redox reagent, Hemmerich and Schmidt86) suggest a radical mechanism of the sensory transduction (assuming that the cyt b photoreduction is photo-tropically relevant). The nature and fate of the flavin-photosubstrate XH remains obsure. For the case X = cyt b the scheme represents a reversed respiration electron pathway...

Various information networks such as gene, intercellular, intracellular, sensory, and brain information networks are implemented in biological systems. The information transduction, conduction, and retreaval functions are integrated in these bioinformation networks. Every bioinformation network is totally consisted of organic molecules including protein. A keen interest has been focused on the molecular mechanisms of the information transduction by the biomolecular assemblies because of their excellent selectivity and sensitivity. This chapter concerns protein molecular... 

Villet R. H. (1978) Mechanism of insect sex-pheromone sensory transduction role of adenyl cyclase. Comp. Biochem. Physiol. 61C, 389-394. 

Breer H., Boekhoff I., Krieger J., Raming K., Strotmann J. and Tareilus E. (1992) Molecular mechanism of olfactory signal transduction. In Sensory Transduction, eds D. P. Corey and S. D., Roper, pp. 94-108. The Rockfeller University Press, New York. 

Do these diverse compounds give rise to a common perception of sweetness or to qualitatively different sensations Sweetness does indeed appear to be a unitary percept (Breslin et al. 1994,1996). However, some sweeteners may be discriminable on the basis of their activation of other sensory transduction mechanisms or differences in the temporal properties of their sensory action. For example, the sweetener sodium saccharin activates bitter receptors in some people (Kuhn et al. 2004 Pronin et al. 2007), and also inhibits sweet taste at high concentrations (Galindo-Cuspinera et al. 2006). Sweet proteins such as thaumatin and monellin can have a slow onset or evoke a prolonged sweetness compared with sugars (Faus 2000), likely owing to a relatively high affinity for the sweet taste receptor. 

How do our sensory systems work How are the initial stimuli detected How are these initial biochemical events transformed into perceptions and experiences We have already encountered systems that sense and respond to chemical signals—namely, receptors that bind to growth factors and hormones. Our knowledge of these receptors and their associated signal-transduction pathways provides us with concepts and tools for unraveling some of the workings of sensory systems. For example, 7TM receptors (seven-transmembrane receptors. Section 14.1) play key roles in olfaction, taste, and vision. Ion channels that are sensitive to mechanical stress are essential for hearing and touch. 

---