Salt receptor

There is controversy about the nature of the salt receptor. In one theory, Na" " ions enter the sensory cells through a sodium channel (this is distinct from the sodium channels of nerve andmuscle cells), causing membrane depolarization, entry of Ca " ", and generation of an action potential. We sense salty. Acids create the sensation of sour think about lemon juice or vinegar. In one mechanism, and there may be more than one, the H+ ions derived from acids block K+ channels. Blockage of these channels, basically responsible for maintaining the membrane potential, leads to membrane depolarization, Ca + entry, and so on. We sense sour. 

Scheme 2. Two-step process for extraction of salt, M+A, using a salt receptor R. Aqueous/organic extraction (eq 1) and solid/organic extraction (eq 2). (Reprinted with permission from ref. 23. Copyright 2004 American Chemical Society.)...

Figure 16. Mono and di-crown appended amido pyrrole salt receptors.

Figure 17. Contact ion-pair salt receptor schematic and crystallographic representation (X-ray structure shows receptor with methanol and water bound. Non-acidic receptor hydrogen atoms removed for clarity).

Michel WC (1999) Cyclic nucleotide-gated channel activation is not required for activity-dependent labeling of zebrafish olfactory receptor neurons by amino adds. Biol Signals Recept 8 338-347 Michel WC, Derbidge DS (1997) Evidence of distinct amino acid and bile salt receptors in the olfactory system of the zebrafish, Danio rerio. Brain Res 764 179-187 Michel WC, Sanderson MJ, Olson JK, Lipschitz DL (2003) Evidence of a novel transduction pathway mediating detection of polyamines by the zebrafish olfactory system. J Exp Biiol 206 1697-1706... 

Chart 3 Compounds 12-15 are recent examples of salt receptors. Compounds 16-18 are examples of salt recognition as a method of supramolecular self-assembly. 

Michel, W. C., and Derbidge, D. S. (1997), Evidence Of Distinct Amino Acid and Bile Salt Receptors In the Olfactory System Of the Zebrafish, Danio Rerio. Brain Research, 764, 179-187. 

The bark of Scutia buxifolia (Rhamnaceae) contains scut-ianine A, B (20), C, D, F (21), and G (22). Similar compounds have been isolated from the roots of Melochia tomen-tosa (23 and 24). A number of 14-membered-ring peptide alkaloids have been isolated from members of the genus Zizyphus (Rhamnaceae) (Fig. 37.8). An alkaloid from diis family, ziziphin (25), blocks activity of the sugar (but not the salt) receptors of flies (Stiidler, 1984). 

A special type of deterrent effect was shown by Ma (1977b). A sesquiterpene dialdehyde isolated from the warburgia plant blocks the sugar receptor cell of S. exempta for 10-20 min after two contacts of 3 min. This inhibitory effect on the sensory neuron has been correlated with a suppression of the feeding response to sucrose. Similarly, Kennedy and Halpern (1980) showed that ziziphin, a cyclic peptide alkaloid of Rhamnaceae, also temporarily inhibits the fly sugar (but not the salt) receptor. 

Fredman, S. M. (1975) Peripheral and central interactions between sugar, water, and salt receptors of the blowfly, Phormia regina. J. Insect Physiol., 21, 265-80. 

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