The end result of both pathways in OSNs is to open calcium channels, I'd be surprised if there was discrimination of enantiomers associated with either pathway. In addition, I've always understood that individual OSNs only have one type of messenger pathway. Therefore, if there is differential activation of secondary messenger pathways by enantiomers the activated pathway is not the source of the difference in reaction to the cue, but an indication of which class of OSNs reacts to the cue. 

Hi Mar,

The mechanisms of the olfactory recognition of enantiomers (in general –isomers) are one of the most intriguing areas in olfaction! Thus well-known pheromone 2,5-dimethylpyrazine (2,5-DMP) which suppresses reproductive function in female mice (e.g. M. Novotny et al., Science, 1986, V. 231, P. 722-724) and influences on spermatogenesis binds odorant-binding protein (OBP) (e.g. J. Pevsner et al., 1985, V. 82, P. 3050-3054). Concerning modern views different OBPs with different binding capabilities to the panel of odorants take significant role in detection, recognition and maybe (?!) further transduction of olfactory cues. However, experimentally was shown that two other DMP isomers (2,3-DMP and 2,6-DMP) have significantly less binding ability (e.g. K.C. Persaud et al., abstract No 112, XVIIIth ECRO Congress, Sept. 3-7, 2008).

Welcome to my RG page.

Good luck,

Sergey

Hi Sergey,

Thank you very much for your answer. I agree that peripheral olfactory events could play an important role in olfactory enantioselectivity. My question was about the further transduction of olfactory signals, i.e. if two enantiomers bind a same receptor (which is known that some enantiomers can do) can they elicit two different signaling cascades? I'm having trouble to find bibliography, as William suggested previously, that one olfactory receptor neuron only express one signalling pathway (the fact that one cascade is found in a neuron does not eliminate the possibility of expression of additional signaling pathways) . 

It's a really interesting question, Mar. I've always viewed perception of olfactory cues as a summation of signals from multiple OSNs, not just one. My assumption, then, would be that differential recognition of enantiomers would be due to each molecule binding to olfactory receptors in multiple OSNs with different affinities specific to each enantiomer/olfactory receptor combination. 

The other thing to consider is the literature (based on what is reviewed in Zielinski and Hara's 2006 chapter "Olfaction") shows that ciliated and microvillous OSNs have different olfactory receptors. Ciliated have G(olf) while microvillous have G(o) receptors. The G(olf) receptors have been demonstrated to activate adenylate cyclase, while G(o) are associated with PLC. Therefore I would consider it unlikely (but not impossible) that there would be differential activation of pathways based on discrimination at the level of receptor binding as each of the pathways are activated by different receptors. That being said, there really hasn't been much done in this area and your hypothesis could very well be correct.