A Selective PMCA Inhibitor Does Not Prolong the Electroolfactogram in Mouse

Within the cilia of vertebrate olfactory receptor neurons, Ca(2+) accumulates during odor transduction. Termination of the odor response requires removal of this Ca(2+), and prior evidence suggests that both Na(+)/Ca(2+) exchange and plasma membrane Ca(2+)-ATPase (PMCA) contribute to this removal.In intact mouse olfactory epithelium, we measured the time course of termination of the odor-induced field potential. Replacement of mucosal Na(+) with Li(+), which reduces the ability of Na(+)/Ca(2+) exchange to expel Ca(2+), prolonged the termination as expected. However, treating the epithelium with the specific PMCA inhibitor caloxin 1b1 caused no significant increase in the time course of response termination.Under these experimental conditions, PMCA does not contribute detectably to the termination of the odor response

A Framework for Exploring Functional Variability in Olfactory Receptor Genes

BACKGROUND: Olfactory receptors (ORs) are the largest gene family in mammalian genomes. Since nearly all OR genes are orphan receptors, inference of functional similarity or differences between odorant receptors typically relies on sequence comparisons. Based on the alignment of entire coding region sequence, OR genes are classified into families and subfamilies, a classification that is believed to be a proxy for OR gene functional variability. However, the assumption that overall protein sequence diversity is a good proxy for functional properties is untested. METHODOLOGY: Here, we propose an alternative sequence-based approach to infer the similarities and differences in OR binding capacity. Our approach is based on similarities and differences in the predicted binding pockets of OR genes, rather than on the entire OR coding region. CONCLUSIONS: Interestingly, our approach yields markedly different results compared to the analysis based on the entire OR coding-regions. While neither approach can be tested at this time, the discrepancy between the two calls into question the assumption that the current classification reliably reflects OR gene functional variability

Co-regulation of a large and rapidly evolving repertoire of odorant receptor genes

The olfactory system meets niche- and species-specific demands by an accelerated evolution of its odorant receptor repertoires. In this review, we describe evolutionary processes that have shaped olfactory and vomeronasal receptor gene families in vertebrate genomes. We emphasize three important periods in the evolution of the olfactory system evident by comparative genomics: the adaptation to land in amphibian ancestors, the decline of olfaction in primates, and the delineation of putative pheromone receptors concurrent with rodent speciation. The rapid evolution of odorant receptor genes, the sheer size of the repertoire, as well as their wide distribution in the genome, presents a developmental challenge: how are these ever-changing odorant receptor repertoires coordinated within the olfactory system? A central organizing principle in olfaction is the specialization of sensory neurons resulting from each sensory neuron expressing only ~one odorant receptor allele. In this review, we also discuss this mutually exclusive expression of odorant receptor genes. We have considered several models to account for co-regulation of odorant receptor repertoires, as well as discussed a new hypothesis that invokes important epigenetic properties of the system

Effects of Li⁺ and caloxin on termination of the odor response.

<p>For each experiment we show the amplitude (amp) in mV and the time constant τ of the recovery from the EOG minimum in ms. The data in the rows marked with an * are included in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0037148#pone-0037148-g002" target="_blank">Figure 2</a>.</p

Control EOG.

<p>(A) At the first arrow, a 100-ms stimulus of unodorized air was applied to the turbinate. At the second arrow, a 100-ms stimulus of isoamyl acetate was applied. The amplitude was 4.4 mV. (B) The first 4500 ms of the recovery from the minimum of the EOG in A are plotted (green) along with a regression curve (black; y = A<i>e</i>^−t/τ+c). The R² for the fit was 0.993 and the time constant of the recovery, τ, was 617 ms.</p

EOG changes over time.

<p>The EOG was recorded before and after each of several treatments. Each treatment consisted of applying solution to the tissue for about 5 min (horizontal bars). The amplitudes of the EOG (X's) and the time constants (filled circles) were measured and plotted. (A) 3 repeated treatments with control Ringer (R). The EOG amplitudes transiently decreased after each treatment while the time constant changed little. (B) The EOG was recorded before and after a Ringer treatment (R), then treatment with a Li⁺-replaced Ringer (L), and then after rinsing the tissue with Ringer and a Ringer treatment (R). The Li⁺-replaced Ringer caused an increase in the time constant. (C) The EOG was recorded after a Ringer treatment (R), then treatment with Ringer containing 100 µM caloxin (C), and then after rinsing the tissue with Ringer and a subsequent Ringer treatment (R). The time constant changed little after caloxin treatment.</p