Caprio J, Byrd R P
J Gen Physiol. 1984 Sep;84(3):403-22. doi: 10.1085/jgp.84.3.403.
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 EOG 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-alpha-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-gamma-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.
电生理实验表明，斑点叉尾鮰的嗅觉感受器含有针对酸性（A）、碱性（B）和中性氨基酸的不同受体位点；此外，至少存在两个部分相互作用的中性位点，一个针对含有短侧链的亲水性中性氨基酸（SCN），另一个针对含有长侧链的疏水性氨基酸（LCN）。交叉适应的程度是通过比较在仅用水持续冲洗嗅觉黏膜（对照）期间和在八种“适应”氨基酸处理的每一种期间，对20种“测试”氨基酸的电嗅觉图（EOG）反应来确定的。适应和测试氨基酸的浓度都进行了调整，以在未适应状态下提供大致相等的反应幅度。在所有八种适应处理下，测试EOG反应都比未适应状态下获得的反应有所降低，但根据适应刺激的分子结构，产生了显著的数量差异。对测试刺激的EOG反应模式的分析确定并表征了各自的“转导过程”，该术语用于描述由特定氨基酸刺激子集引发的膜事件，这些事件与嗅觉感受器电位的起源密切相关。只有当刺激化合物与不同的转导过程相互作用时，才假定刺激与不同的膜“位点”结合。本报告中确定的四个相对独立的L-α-氨基酸转导过程（因此至少有四个结合位点）包括：（a）天冬氨酸和谷氨酸的A过程；（b）精氨酸和赖氨酸的B过程；（c）甘氨酸、丙氨酸、丝氨酸、谷氨酰胺以及可能的半胱氨酸的SCN过程；（d）甲硫氨酸、乙硫氨酸、缬氨酸、正缬氨酸、亮氨酸、正亮氨酸、γ-甲基谷氨酸酯、组氨酸、苯丙氨酸以及也可能的半胱氨酸的LCN过程。鲶鱼中这些嗅觉转导过程的特异性与其他鱼类中通过生化方法确定的氨基酸受体位点的特异性以及多种生物体组织中的氨基酸转运特异性相似。
