Electrophysiological evidence for acidic, basic, and neutral amino acid olfactory receptor sites in the catfish.

Abstract

Electrophysiological experiments indicate that olfactory receptors of the channel catfish, Ictalurus punctatus, contain different receptor sites for the acidic (A), basic (B), and neutral amino acids ; further, at least two partially interacting neutral sites exist, one for the hydrophilic neutral amino acids containing short side chains (SCN), and the second for the hydrophobic amino acids containing long side chains (LCN) . The extent of cross-adaptation was determined by comparing the electro-olfactogram (EOG) responses to 20 "test" amino acids during continuous bathing of the olfactory mucosa with water only (control) to those during each of the eight "adapting" amino acid regimes. Both the adapting and test amino acids were adjusted in concentrations to provide approximately equal response magnitudes in the unadapted state . Under all eight adapting regimes, the test FOG responses were reduced from those obtained in the unadapted state, but substantial quantitative differences resulted, depending upon the molecular structure of the adapting stimulus . Analyses of the patterns of EOG responses to the test stimuli identified and characterized the respective "transduction processes," a term used to describe membrane events initiated by a particular subset of amino acid stimuli that are intricately linked to the origin of the olfactory receptor potential . Only when the stimulus compounds interact with different transduction processes are the stimuli assumed to bind to different membrane "sites." Four relatively independent L-a-amino acid transduction processes (and thus at least four binding sites) identified in this report include : (a) the A process for aspartic and glutamic acids ; (b) the B process for arginine and lysine ; (c) the SCN process for glycine, alanine, serine, glutamine, and possibly cysteine ; (d) the LCN process for methionine, ethionine, valine, norvaline, leucine, norleucine, glutamic acid-7-methyl ester, histidine, phenylalanine, and also possibly cysteine . The specificities of these olfactory transduction processes in the catfish are similar to those for the biochemically determined receptor sites for amino acids in other species of fishes and to amino acid transport specificities in tissues of a variety of organisms .Address reprint requests to Dr.

Olfactory morphology and physiology of elasmobranchs

“…Some interspecific variability in the relative effectiveness of the 20 amino acids tested at 10 -4.2 moll -1 was observed but the neutral amino acids, such as alanine, serine and methionine, were generally highly stimulatory (Table3). Neutral amino acids were previously demonstrated to be especially potent stimuli for a few elasmobranch species and for teleost fishes (Caprio and Byrd, 1984;Silver, 1979;Tricas et al, 2009;Zeiske et al, 1986). Tricas et al (Tricas et al, 2009) found that the response of scalloped hammerhead sharks to cysteine was about twice that for alanine; however, cysteine was a less effective stimulus for the five species we tested (44-75% of alanine), which included another sphyrnid species.…”

Evidence for partial overlap of male olfactory cues in lampreys

“…Responses were normalized by the response to L-arginine at 1×10 −5 mol l −1 (Siefkes and Li, 2004). The specificity with which P. marinus detected conspecific and heterospecific odours was determined using cross-adaptation experiments (Caprio and Byrd, 1984). Cross-adaptation experiments record the responses to a stimulus while the epithelium is saturated with a second stimulus (the adapting stimulus).…”

Olfactory sensitivity to steroid glucuronates in Mozambique tilapia suggests two distinct and specific receptors for pheromone detection

“…If the 'test' and 'adapting' odorant act through independent olfactory receptor sites, the response to the test odorant during adaptation should be unaffected, i.e. not greatly reduced, compared to the signal measured prior to adaptation (Caprio and Byrd, 1984;Cole and Stacey, 2006;Sorensen et al, 1995). In binary mixture tests, receptor sites are separate if the EOG response to a mixture of two odorants is approximately the sum of the responses to the individual odorants given alone.…”