Previously, we have detected the expression of 2 lipocalin genes (lp1 and lp2) in the olfactory epithelium of the Japanese newt Cynops pyrrhogaster. Recombinant proteins of these genes (Cp-Lip1 and Cp-Lip2, respectively) exhibited high affinities to various odorants, suggesting that they work like the odorant-binding proteins (OBPs). However, the physiological functions of OBP generally remain inconclusive. Here, we examined the effect of Cp-Lip1 on the electrophysiological responses of newt olfactory receptor cells. We observed that the electro-olfactogram induced by the vapor of an odorant with high affinity to Cp-Lip1 appeared to increase in amplitude when a tiny drop of Cp-Lip1 solution was dispersed over the olfactory epithelium. However, the analysis was difficult because of possible interference by intrinsic components in the nasal mucus. We subsequently adopted a mucus-free condition by using suction electrode recordings from isolated olfactory cells, in which impulses were generated by puffs of odorant solution. When various concentration (0-5 µM) of Cp-Lip1 was mixed with the stimulus solution of odorants highly affinitive to Cp-Lip1, the impulse frequency increased in a concentration-dependent manner. The increase by Cp-Lip1 was seen more evidently at lower concentration ranges of stimulus odorants. These results strongly suggest that Cp-Lip1 broadens the sensitivity of the olfactory cells toward the lower concentration of odorants, by which animals can detect very low concentration of odorants.

中文翻译：

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Lipocalin Cp-Lip1在New嗅觉受体细胞中增强嗅觉反应的电生理研究。

以前，我们已经检测到日本new Cynops pyrrhogaster的嗅上皮中2个lipocalin基因的表达（lp1和lp2）。这些基因的重组蛋白（分别为Cp-Lip1和Cp-Lip2）表现出对各种气味剂的高亲和力，表明它们像气味剂结合蛋白（OBPs）一样起作用。然而，OBP的生理功能通常仍然不确定。在这里，我们检查了Cp-Lip1对new嗅觉受体细胞电生理反应的影响。我们观察到，当一小滴Cp-Lip1溶液散布在嗅觉上皮细胞上时，由对Cp-Lip1具有高亲和力的增味剂的蒸汽诱导的电子嗅觉图似乎在幅度上有所增加。但是，由于鼻粘液中固有成分的干扰可能会造成分析困难。随后，我们通过使用来自分离的嗅觉细胞的抽吸电极记录来采用无粘液条件，其中的冲动是由一团气味溶液产生的。当将各种浓度（0-5 µM）的Cp-Lip1与高度亲和Cp-Lip1的增味剂刺激溶液混合时，脉冲频率会随浓度而增加。在较低的刺激性气味剂浓度范围内，Cp-Lip1的增加更为明显。这些结果强烈表明，Cp-Lip1扩大了嗅觉细胞对低浓度气味剂的敏感性，从而使动物可以检测到极低浓度的气味剂。当将各种浓度（0-5 µM）的Cp-Lip1与高度亲和Cp-Lip1的增味剂刺激溶液混合时，脉冲频率会随浓度而增加。在较低的刺激性气味剂浓度范围内，Cp-Lip1的增加更为明显。这些结果强烈表明，Cp-Lip1扩大了嗅觉细胞对低浓度气味剂的敏感性，从而使动物可以检测到极低浓度的气味剂。当将各种浓度（0-5 µM）的Cp-Lip1与高度亲和Cp-Lip1的增味剂刺激溶液混合时，脉冲频率会随浓度而增加。在较低的刺激性气味剂浓度范围内，Cp-Lip1的增加更为明显。这些结果强烈表明，Cp-Lip1扩大了嗅觉细胞对低浓度气味剂的敏感性，从而使动物可以检测到极低浓度的气味剂。