Kurahashi T, Yau K W
Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Nature. 1993 May 6;363(6424):71-4. doi: 10.1038/363071a0.
Odorant stimulation leads to a depolarization of olfactory receptor neurons. A mechanism underlying this transduction, which occurs in the sensory cilia, involves a G-protein-mediated increase in adenylyl cyclase activity, and therefore a rise in internal cyclic AMP and consequent opening of a cAMP-gated cation channel on the plasma membrane. Another mechanism, not as well established, involves the opening of an inositol trisphosphate-activated cation channel on the plasma membrane as a result of phospholipase C activity. In both cases, an influx of cations is thought to generate the depolarizing receptor potential. We now report, however, that the mechanism is actually more complex. The odorant-induced current appears to contain an inward chloride component also, which is triggered by calcium influx through the cation-selective channel. This newly found chloride component can be as large as the cationic component. The co-existence of cationic and chloride components in the odorant response, possibly unique among sensory transduction mechanisms, may serve to reduce variations in the transduction current resulting from changes in external ionic concentrations around the olfactory cilia. Our finding can explain the long-standing puzzle of why removal of most mucosal cations still does not diminish the amplitude of the olfactory receptor cell response.
气味刺激会导致嗅觉受体神经元去极化。这种发生在感觉纤毛中的转导机制，涉及G蛋白介导的腺苷酸环化酶活性增加，进而导致细胞内环状AMP升高，随后质膜上的cAMP门控阳离子通道打开。另一种尚未完全明确的机制，是由于磷脂酶C的活性，导致质膜上的三磷酸肌醇激活阳离子通道打开。在这两种情况下，阳离子内流被认为会产生去极化受体电位。然而，我们现在报告，该机制实际上更为复杂。气味诱导的电流似乎还包含内向氯离子成分，它是由钙离子通过阳离子选择性通道内流触发的。这个新发现的氯离子成分可能与阳离子成分一样大。气味反应中阳离子和氯离子成分的共存，这在感觉转导机制中可能是独一无二的，可能有助于减少因嗅觉纤毛周围外部离子浓度变化而导致的转导电流变化。我们的发现可以解释一个长期存在的谜题，即为什么去除大多数黏膜阳离子仍然不会降低嗅觉受体细胞反应的幅度。
