Figure 4.

Proposed models for salt perception. Two models are proposed for sensing low and high concentration of salts in food. (a,b) In the 2 cells model, one general-salt cell is tuned to a broad spectrum of salt concentrations and the other only responds to high salt levels, the high-salt cell. At low salt levels (a), the general-salt cell triggers a feeding message. At high-salt levels (b), the NO/sGC/cGMP cascade is activated in the high-salt cell resulting in a “no feeding” message to the brain, which overwhelms the “feeding” message produced by the general-salt cell. (c,d) In the 1 cell model, only one salt-receptor cell is enough for salt concentration discrimination. At low salt, the NO/sGC/cGMP cascade is inactive, and this salt detector produces a “feeding” signal upon low salt levels. At high salt, the NO/sGC/cGMP cascade is activated within this cell and the feeding message turns to “no feeding”. Putative sodium receptors are drawn as square boxes.