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Istituto di Cibernetica e Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy.
Biophys Chem. 1995 Aug;55(3):185-96. doi: 10.1016/0301-4622(94)00153-b.
Rod and cone photoreceptors are the light detectors in the visual system whereas olfactory receptor cells are the odorant detectors in the olfactory system. Despite the two very different types of stimuli, light in photoreceptors, and odorant molecules in olfactory receptor cells, the mechanisms of visual and olfactory transduction appear to have many homologies. Both stimuli trigger a chain of enzymatic events that terminates in a change in the concentration of a cyclic nucleotide: a decrease in the concentration of cGMP in photoreceptors, and an increase in the concentration of cAMP in olfactory receptor cells. These cyclic nucleotides directly gate cation channels and therefore a change in their concentration induced by the external stimulus is converted into an electrical signal. The analysis of the ionic selectivity properties of cyclic nucleotidegated channels in retinal rods, cones and in olfactory receptor cells shows that there are many similarities between these channels. They do not appreciably select between alkali monovalent cations and can be permeated and blocked by divalent cations. Their ionic permeation properties are consistent with the presence of a cation-binding site of high-field strength in the pore.
视杆和视锥光感受器是视觉系统中的光探测器，而嗅觉受体细胞是嗅觉系统中的气味探测器。尽管光感受器所接收的光刺激和嗅觉受体细胞所接收的气味分子刺激这两种刺激类型截然不同，但视觉和嗅觉转导机制似乎有许多同源性。两种刺激都引发一系列酶促事件，最终导致环核苷酸浓度发生变化：光感受器中cGMP浓度降低，嗅觉受体细胞中cAMP浓度升高。这些环核苷酸直接控制阳离子通道，因此由外部刺激引起的其浓度变化会转化为电信号。对视网膜视杆、视锥以及嗅觉受体细胞中环核苷酸门控通道的离子选择性特性分析表明，这些通道之间存在许多相似之处。它们对单价碱金属阳离子没有明显的选择性，并且可以被二价阳离子通透和阻断。它们的离子通透特性与孔中存在高场强阳离子结合位点一致。
