Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States of America ; Applied Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania, United States of America.
PLoS One. 2013 Sep 2;8(9):e72271. doi: 10.1371/journal.pone.0072271. eCollection 2013.
The odorant partition coefficient is a physicochemical property that has been shown to dramatically influence odorant deposition patterns in the mammalian nose, leading to a chromatographic separation of odorants along the sensory epithelium. It is unknown whether a similar phenomenon occurs in fish. Here we utilize molecular dynamics simulations, based on a simplified molecular model of olfactory mucus, to calculate water/mucus partition coefficients for amino acid odorants (alanine, glycine, cysteine, and valine) that are known to elicit feeding behavior in fish. Both fresh water and salt water environments are considered. In fresh water, all four amino acids prefer the olfactory mucus phase to water, and the partition coefficient is shown to correlate with amino acid hydrophobicity. In salt water, a reversal in odorant partitioning is found, where each of the feeding stimulants (except glycine) prefer the water phase to olfactory mucus. This is due to the interactions between the salt ions and the odorant molecules (in the water phase), and between the salt and simplified mucin (in the olfactory mucus phase). Thus, slightly different odorant deposition patterns may occur in the fish olfactory organ in fresh and salt water environments. However, in both underwater environments we found that the variation of the water/mucus odorant partition coefficient is approximately one order of magnitude, in stark contrast to air/mucus odorant partition coefficients that can span up to six orders of magnitude. We therefore anticipate relatively similar deposition patterns for most amino acid odorants in the fish olfactory chamber. Thus, in contrast to terrestrial species, living in an underwater environment may preclude appreciable chromatographic odorant separation that may be used for spatial coding of odor identity across the olfactory epithelium. This is consistent with the reported lack of spatial organization of olfactory receptor neurons in the fish olfactory epithelium.
气味分配系数是一种物理化学性质，已被证明会极大地影响哺乳动物鼻子中气味剂的沉积模式，导致气味剂沿着感觉上皮呈色谱分离。目前尚不清楚这种类似的现象是否会在鱼类中发生。在这里，我们利用基于嗅觉粘液简化分子模型的分子动力学模拟，计算出已知会引起鱼类摄食行为的氨基酸气味剂（丙氨酸、甘氨酸、半胱氨酸和缬氨酸）在水/粘液中的分配系数。同时考虑了淡水和盐水环境。在淡水中，所有四种氨基酸都优先选择嗅觉粘液相而不是水相，并且分配系数与氨基酸疏水性相关。在盐水中，发现气味剂分配发生逆转，除了甘氨酸之外，所有的摄食刺激剂（except glycine）都优先选择水相而不是嗅觉粘液相。这是由于盐离子与气味剂分子（在水相）之间以及盐与简化粘蛋白（在嗅觉粘液相）之间的相互作用所致。因此，在淡水和盐水环境中，鱼类嗅觉器官中可能会出现略微不同的气味剂沉积模式。然而，在这两种水下环境中，我们发现水/粘液气味剂分配系数的变化约为一个数量级，与空气/粘液气味剂分配系数形成鲜明对比，后者可以跨越多达六个数量级。因此，我们预计在鱼类嗅觉腔内，大多数氨基酸气味剂的沉积模式会相对相似。因此，与陆地物种不同，生活在水下环境中可能会排除可能用于跨嗅觉上皮对气味身份进行空间编码的明显色谱气味分离。这与鱼类嗅觉上皮中嗅觉受体神经元缺乏空间组织的报道一致。
