Neuronal receptors biological roles

The tumor necrosis factor (TNF) receptor (TNFR) superfamily comprises more than 20 type-I transmembrane proteins that are structurally related in their extracellular domains and specifically activated by the corresponding superfamily of TNF-like ligands (Locksley et al, 2001). Members of this receptor superfamily are widely distributed and play important roles in many crucial biological processes such as lymphoid and neuronal development, innate and adaptive immunity, and maintenance of cellular homeostasis. Agents that manipulate the signaling of these receptors are being used or showing promise towards the treatment and prevention of many human diseases (Ashkenazi and Dixit, 1998 Leonen, 1998 Newton and Decicco, 1999). 

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. 

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