Real-time In Vitro Monitoring of Odorant Receptor Activation by an Odorant in the Vapor Phase

Roles of sensory receptors in non-sensory organs: the kidney and beyond

Olfactory receptors (ORs), taste receptors and opsins are well-known for their pivotal roles in mediating the senses of smell, taste and sight, respectively. However, in the past two decades, research has shown that these sensory receptors also regulate physiological processes in a variety of non-sensory tissues. Although ORs, taste receptors and opsins have all been shown to have physiological roles beyond their traditional locations, most work in the kidney has focused on ORs. To date, renal ORs have been shown to have roles in blood pressure regulation (OLFR78 and OLFR558) and glucose homeostasis (OLFR1393). However, sensory receptors remain drastically understudied outside of traditional sensory systems, in part because of inherent challenges in studying these receptors. Increased knowledge of the physiological and pathophysiological roles of sensory receptors has the potential to substantially improve understanding of the function of numerous organs and systems, including the kidney. In addition, most sensory receptors are G protein-coupled receptors, which are considered to be the most druggable class of proteins, and thus could potentially be exploited as future therapeutic targets.

Antagonistic interactions between odorants alter human odor perception

The olfactory system uses hundreds of odorant receptors (ORs), the largest group of the G-protein-coupled receptor (GPCR) superfamily, to detect a vast array of odorants. Each OR is activated by specific odorous ligands, and like other GPCRs, antagonism can block activation of ORs. Recent studies suggest that odorant antagonisms in mixtures influence olfactory neuron activities, but it is unclear how this affects perception of odor mixtures. In this study, we identified a set of human ORs activated by methanethiol and hydrogen sulfide, two potent volatile sulfur malodors, through large-scale heterologous expression. Screening odorants that block OR activation in heterologous cells identified a set of antagonists, including β-ionone. Sensory evaluation in humans revealed that β-ionone reduced the odor intensity and unpleasantness of methanethiol. Additionally, suppression was not observed when methanethiol and β-ionone were introduced simultaneously to different nostrils. Our study supports the hypothesis that odor sensation is altered through antagonistic interactions at the OR level.

The Luminescence Hypothesis of Olfaction

A new hypothesis for the mechanism of olfaction is presented. It begins with an odorant molecule binding to an olfactory receptor. This is followed by the quantum biology event of inelastic electron tunneling as has been suggested with both the vibration and swipe card theories. It is novel in that it is not concerned with the possible effects of the tunneled electrons as has been discussed with the previous theories. Instead, the high energy state of the odorant molecule in the receptor following inelastic electron tunneling is considered. The hypothesis is that, as the high energy state decays, there is fluorescence luminescence with radiative emission of multiple photons. These photons pass through the supporting sustentacular cells and activate a set of olfactory neurons in near-simultaneous timing, which provides the temporal basis for the brain to interpret the required complex combinatorial coding as an odor. The Luminescence Hypothesis of Olfaction is the first to present the necessity of or mechanism for a 1:3 correspondence of odorant molecule to olfactory nerve activations. The mechanism provides for a consistent and reproducible time-based activation of sets of olfactory nerves correlated to an odor. The hypothesis has a biological precedent: an energy feasibility assessment is included, explaining the anosmia seen with COVID-19, and can be confirmed with existing laboratory techniques.