Kawai Fusao, Miyachi Ei-ichi
Department of Physiology, School of Medicine, Fujita Health University, Toyoake, Japan.
Nihon Shinkei Seishin Yakurigaku Zasshi. 2007 Nov;27(5-6):201-5.
The first step in olfactory sensation involves the binding of odorant molecules to specific receptor proteins on the ciliary surface of olfactory receptor cells (ORCs). Odorant receptors coupled to G-proteins activate adenylyl cyclase leading to the generation of cAMP, which directly gates a cyclic nucleotide-gated cationic channel in the ciliary membrane. This initial excitation causes a slow and graded depolarizing voltage change, which is encoded into a train of action potentials. Action potentials of ORCs are generated by voltage-gated Na- currents and T-type Ca2- currents in the somatic membrane. Isolated ORCs that have lost their cilia during the dissociation procedure are known to exhibit spike frequency accommodation by injecting the steady current. This raises the possibility that somatic ionic channels in ORCs may serve for odor adaptation at the level of spike encoding, although odor adaptation is mainly accomplished by the ciliary transduction machinery. This review discusses current knowledge concerning the mechanisms of spike generation in ORCs. It also reviews how neurotransmitters and hormones modulate ionic currents and action potentials in ORCs.
嗅觉感受的第一步涉及气味分子与嗅觉受体细胞（ORC）纤毛表面特定受体蛋白的结合。与G蛋白偶联的气味受体激活腺苷酸环化酶，导致cAMP的产生，cAMP直接开启纤毛膜中的环核苷酸门控阳离子通道。这种初始兴奋会引起缓慢且分级的去极化电压变化，该变化被编码为一串动作电位。ORC的动作电位由体细胞膜中的电压门控Na+电流和T型Ca2+电流产生。已知在解离过程中失去纤毛的分离ORC通过注入稳定电流表现出峰频率适应性。这增加了一种可能性，即ORC中的体细胞离子通道可能在峰编码水平上参与气味适应，尽管气味适应主要由纤毛转导机制完成。本文综述了关于ORC中峰产生机制的当前知识。它还回顾了神经递质和激素如何调节ORC中的离子电流和动作电位。
