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Abstract Background Extracellular nucleotides have long been known to play neuromodulatory roles and to be involved in intercellular signalling. In the olfactory system, ATP is released by olfactory neurons, and exogenous ATP can evoke an increase in intracellular calcium concentration in sustentacular cells, the nonneuronal supporting cells of the olfactory epithelium. Here we investigate the hypothesis that olfactory neurons communicate with sustentacular cells via extracellular ATP and purinergic receptor activation. Results Here we show that exposure of mice to a mixture of odorants induced a significant increase in the levels of the transcription factor CREB phosphorylated at Ser-133 in the nuclei of both olfactory sensory neurons and sustentacular cells. This activation was dependent on adenylyl cyclase III-mediated olfactory signaling and on activation of P2Y purinergic receptors on sustentacular cells. Purinergic receptor antagonists inhibited odorant-dependent CREB phosphorylation specifically in the nuclei of the sustentacular cells. Conclusion Our results point to a possible role for extracellular nucleotides in mediating intercellular communication between the neurons and sustentacular cells of the olfactory epithelium in response to odorant exposure. Maintenance of extracellular ionic gradients and metabolism of noxious chemicals by sustentacular cells may therefore be regulated in an odorant-dependent manner by olfactory sensory neurons.

The olfactory signal transduction cascade transforms odor information into electrical signals by a cAMP-based amplification mechanism. The mechanisms underlying the very precise temporal and spatial organization of the relevant signaling components remains poorly understood. Here, we identify, using co-immunoprecipitation experiments, a macromolecular assembly of signal transduction components in mouse olfactory neurons, organized through MUPP1. Disruption of the PDZ signaling complex, through use of an inhibitory peptide, strongly impaired odor responses and changed the activation kinetics of olfactory sensory neurons. In addition, our experiments demonstrate that termination of the response is dependent on PDZ-based scaffolding. These findings provide new insights into the functional organization, and regulation, of olfactory signal transduction. [ABSTRACT FROM AUTHOR]

Despite increasing knowledge about dimerization of G-protein-coupled receptors, nothing is known about dimerization in the largest subfamily, odorant receptors. Using a combination of biochemical and electrophysiological approaches, we demonstrate here that odorant receptors can dimerize. DOR83b, an odorant receptor that is ubiquitously expressed in olfactory neurons from Drosophila melanogaster and highly conserved among insect species, forms heterodimeric complexes with other odorant-receptor proteins, which strongly increases their functionality. [ABSTRACT FROM AUTHOR]

The mechanism of CF 3 transfer from R 3 SiCF 3 (R = Me, Et, iPr) to ketones and aldehydes, initiated by M + X - (<0.004 to 10 mol %), has been investigated by analysis of kinetics (variable-ratio stopped-flow NMR and IR), 13 C/ 2 H KIEs, LFER, addition of ligands (18-c-6, crypt-222), and density functional theory calculations. The kinetics, reaction orders, and selectivity vary substantially with reagent (R 3 SiCF 3 ) and initiator (M + X - ). Traces of exogenous inhibitors present in the R 3 SiCF 3 reagents, which vary substantially in proportion and identity between batches and suppliers, also affect the kinetics. Some reactions are complete in milliseconds, others take hours, and others stall before completion. Despite these differences, a general mechanism has been elucidated in which the product alkoxide and CF 3 - anion act as chain carriers in an anionic chain reaction. Silyl enol ether generation competes with 1,2-addition and involves protonation of CF 3 - by the α-C-H of the ketone and the OH of the enol. The overarching mechanism for trifluoromethylation by R 3 SiCF 3 , in which pentacoordinate siliconate intermediates are unable to directly transfer CF 3 - as a nucleophile or base, rationalizes why the turnover rate (per M + X - initiator) depends on the initial concentration (but not identity) of X - , the identity (but not concentration) of M + , the identity of the R 3 SiCF 3 reagent, and the carbonyl/R 3 SiCF 3 ratio. It also rationalizes which R 3 SiCF 3 reagent effects the most rapid trifluoromethylation, for a specific M + X - initiator.