Inhibition of taurine and 5?AMP olfactory receptor sites of the spiny lobster Panulirus argus by odorant compounds and mixtures

Abstract

1. The effects of the odorant compounds adenosine-5'-monophosphate (5'AMP), ammonium, betaine, L-cysteine, L-glutamate, DL-succinate, and taurine and of mixtures of these compounds on binding of taurine and 5'AMP to dendritic membrane from the olfactory organ of spiny lobsters (Panulirus argus) were quantified to evaluate the contribution of inhibition of odorant-receptor binding to the generation of physiological responses to mixtures. 2. Taurine binding sites belong to two affinity classes, while 5'AMP binding sites belong to a single affinity class. Binding of either taurine or 5'AMP was partially inhibited in an apparently noncompetitive, concentration dependent fashion by most odorant compounds, with 25-40% inhibition by 1 mM of odorant. Mixtures of two or more odorant compounds also inhibited binding of taurine or 5'AMP to its sites. However, the inhibition by mixtures was often significantly less than expected from the inhibition produced by a mixture's components assuming either a noncompetitive or competitive mechanism. 3. By including this binding inhibition between compounds into models for predicting physiological responses to mixtures from the responses to the components, the predictive power of the models is significantly improved. This result strongly suggests that binding inhibition can influence the physiological responsiveness of chemoreceptor cells to mixtures.

Symmetry, Stereotypy, and Topography of Odorant Representations in Mouse Olfactory Bulbs

“…How then are they represented within the olfactory bulb? Electrophysiological and psychophysical studies in several species reveal various types of nonlinear interactions that occur in response to odorant mixtures (Derby et al, 1991a,b;Getz and Akers, 1995;Olson and Derby, 1995). These interactions may underlie behavioral observations, such as odor masking and overshadowing (Laing et al, 1989;Derby et al, 1996;Linster and Smith, 1997;Pelz et al, 1997).…”

Regulation of Connexin Channels by pH

“…The affinities of these transporters for taurine range from 4 to 40 M, and there are several regions of potentially significant homology with connexins. An invertebrate odorant receptor has been recently shown to have two high affinity binding sites for taurine (K d values of 18 pM and 6 M), but the amino acid sequence has not yet been determined (56).…”

Responses of olfactory receptor neurons in the spiny lobster to binary mixtures are predictable using a noncompetitive model that incorporates excitatory and inhibitory transduction pathways

“…We have an elementary understanding of the number and specificity of transduction processes from electrophysiological studies of response specificity (Derby et al 1991a) and of cross-adaptation between odorant chemicals , biochemical studies of binding kinetics of radiolabeled odorant compounds (Olson et al 1992;Michel et al 1993;Burgess et al 1994;Olson and Derby 1995), biochemical studies of odor-stimulated production of second messengers (Boekhoff et al 1994), and patch clamp electrophysiological studies of odor-activated conductances and ion channel activity (Michel et al 1991;Michel and Ache 1992;Fadool and Ache 1992;Fadool et al 1993;Ache 1994;Hatt and Ache 1994;Fadool and Ache 1994a&b;Michel and Ache 1994;Simon and Derby 1995). For example, we know that members of the ORN population have different and narrowly tuned excitatory response spectra, including ORNs narrowly tuned to either taurine, L-glutamate, adenosine-5-monophosphate, L-cysteine, or ammonium.…”

“…In addition, there are mechanisms by which these excitatory transduction pathways can be modulated. First, the ability of a receptor to bind an odorant can be inhibited by other compounds in what seems to be a largely noncompetitive manner (Burgess et al 1994;Olson and Derby 1995). In effect, inhibitory compounds act as noncompetitive antagonists by binding to the receptor molecule at a site other than the binding site for the excitatory odorant, which results in a decrease in the binding site affinity.…”