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Mechanism of olfactory masking in the sensory cilia.

Takeuchi H, Ishida H, Hikichi S, Kurahashi T - J. Gen. Physiol. (2009)

Bottom Line: It is interpreted, however, that in the natural odorant response the Cl(Ca) is affected by the reduction of Ca2+ influx through the CNG channels as a secondary effect.We conclude that odorants regulate CNG level to express masking, and Cl(Ca) in the cilia carries out the signal amplification and reduction evenly spanning the entire cilia.The present findings may serve possible molecular architectures to design effective masking agents, targeting olfactory manipulation at the nano-scale ciliary membrane.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Frontier Biosciences, Osaka University, Osaka 560-8531, Japan.

ABSTRACT
Olfactory masking has been used to erase the unpleasant sensation in human cultures for a long period of history. Here, we show a positive correlation between the human masking and the odorant suppression of the transduction current through the cyclic nucleotide-gated (CNG) and Ca2+-activated Cl- (Cl(Ca)) channels. Channels in the olfactory cilia were activated with the cytoplasmic photolysis of caged compounds, and their sensitiveness to odorant suppression was measured with the whole cell patch clamp. When 16 different types of chemicals were applied to cells, cyclic AMP (cAMP)-induced responses (a mixture of CNG and Cl(Ca) currents) were suppressed widely with these substances, but with different sensitivities. Using the same chemicals, in parallel, we measured human olfactory masking with 6-rate scoring tests and saw a correlation coefficient of 0.81 with the channel block. Ringer's solution that was just preexposed to the odorant-containing air affected the cAMP-induced current of the single cell, suggesting that odorant suppression occurs after the evaporation and air/water partition of the odorant chemicals at the olfactory mucus. To investigate the contribution of Cl(Ca), the current was exclusively activated by using the ultraviolet photolysis of caged Ca, DM-nitrophen. With chemical stimuli, it was confirmed that Cl(Ca) channels were less sensitive to the odorant suppression. It is interpreted, however, that in the natural odorant response the Cl(Ca) is affected by the reduction of Ca2+ influx through the CNG channels as a secondary effect. Because the signal transmission between CNG and Cl(Ca) channels includes nonlinear signal-boosting process, CNG channel blockage leads to an amplified reduction in the net current. In addition, we mapped the distribution of the Cl(Ca) channel in living olfactory single cilium using a submicron local [Ca2+]i elevation with the laser photolysis. Cl(Ca) channels are expressed broadly along the cilia. We conclude that odorants regulate CNG level to express masking, and Cl(Ca) in the cilia carries out the signal amplification and reduction evenly spanning the entire cilia. The present findings may serve possible molecular architectures to design effective masking agents, targeting olfactory manipulation at the nano-scale ciliary membrane.

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Human olfactory masking and correlation with the blockage of transduction current. (A) Human olfactory masking score. Data obtained with 16 chemical samples (see Table I) from 20 human subjects. Test odor used was iso-valeric acid, and sample numbers correspond to the numbers in Table I. Plots indicate means, and bars show SD. The higher masking scores indicate the greater masking effect. (B) Correlation between human olfactory masking score and ppm concentration. Note that both variables show no correlation (R = 0.17). (C) Correlation between human olfactory masking score and channel score. 0.1% nominal concentration. Note that both variables show positive correlation (R = 0.81). 16 data were obtained from Figs. 1 D and 2 A. (D) Correlation between human olfactory masking score and channel score. Data from 13 chemicals. Linear regression gave R of 0.62. 0.01% nominal concentration.
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fig2: Human olfactory masking and correlation with the blockage of transduction current. (A) Human olfactory masking score. Data obtained with 16 chemical samples (see Table I) from 20 human subjects. Test odor used was iso-valeric acid, and sample numbers correspond to the numbers in Table I. Plots indicate means, and bars show SD. The higher masking scores indicate the greater masking effect. (B) Correlation between human olfactory masking score and ppm concentration. Note that both variables show no correlation (R = 0.17). (C) Correlation between human olfactory masking score and channel score. 0.1% nominal concentration. Note that both variables show positive correlation (R = 0.81). 16 data were obtained from Figs. 1 D and 2 A. (D) Correlation between human olfactory masking score and channel score. Data from 13 chemicals. Linear regression gave R of 0.62. 0.01% nominal concentration.

Mentions: To investigate human masking with 16 chemicals used in cell experiments, we attempted to obtain masking scores (obtained by a 6-scale rating of 0–5) with psychophysical measurements from human subjects. To achieve this, the subjects were exposed to the “test vapor” (iso-valeric acid) under the presence of a variety of “masking vapors.” Because volatile chemicals usually express their intrinsic smells, the subjects had to extract the test smell exclusively, even under the different smell conditions. We used expert subjects who have expertise in extracting specific smells under different conditions. Fig. 2 A shows results obtained from 20 subjects. The data show that olfactory masking occurs with many types of volatiles and also indicate variations in the masking effects depending on the samples. For the 16 chemicals used in this work, the masking scores did not show statistical correlations with the real activities of substances in the testing container (Fig. 2 B). Therefore, it is interpreted that we could exclude a factor, the evaporation rate and/or the vapor pressure of the chemicals, which determines the access rate of volatile chemicals to the olfactory epithelium. In the cell experiments described above, such an access rate is not included in the experimental process.


Mechanism of olfactory masking in the sensory cilia.

Takeuchi H, Ishida H, Hikichi S, Kurahashi T - J. Gen. Physiol. (2009)

Human olfactory masking and correlation with the blockage of transduction current. (A) Human olfactory masking score. Data obtained with 16 chemical samples (see Table I) from 20 human subjects. Test odor used was iso-valeric acid, and sample numbers correspond to the numbers in Table I. Plots indicate means, and bars show SD. The higher masking scores indicate the greater masking effect. (B) Correlation between human olfactory masking score and ppm concentration. Note that both variables show no correlation (R = 0.17). (C) Correlation between human olfactory masking score and channel score. 0.1% nominal concentration. Note that both variables show positive correlation (R = 0.81). 16 data were obtained from Figs. 1 D and 2 A. (D) Correlation between human olfactory masking score and channel score. Data from 13 chemicals. Linear regression gave R of 0.62. 0.01% nominal concentration.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2713142&req=5

fig2: Human olfactory masking and correlation with the blockage of transduction current. (A) Human olfactory masking score. Data obtained with 16 chemical samples (see Table I) from 20 human subjects. Test odor used was iso-valeric acid, and sample numbers correspond to the numbers in Table I. Plots indicate means, and bars show SD. The higher masking scores indicate the greater masking effect. (B) Correlation between human olfactory masking score and ppm concentration. Note that both variables show no correlation (R = 0.17). (C) Correlation between human olfactory masking score and channel score. 0.1% nominal concentration. Note that both variables show positive correlation (R = 0.81). 16 data were obtained from Figs. 1 D and 2 A. (D) Correlation between human olfactory masking score and channel score. Data from 13 chemicals. Linear regression gave R of 0.62. 0.01% nominal concentration.
Mentions: To investigate human masking with 16 chemicals used in cell experiments, we attempted to obtain masking scores (obtained by a 6-scale rating of 0–5) with psychophysical measurements from human subjects. To achieve this, the subjects were exposed to the “test vapor” (iso-valeric acid) under the presence of a variety of “masking vapors.” Because volatile chemicals usually express their intrinsic smells, the subjects had to extract the test smell exclusively, even under the different smell conditions. We used expert subjects who have expertise in extracting specific smells under different conditions. Fig. 2 A shows results obtained from 20 subjects. The data show that olfactory masking occurs with many types of volatiles and also indicate variations in the masking effects depending on the samples. For the 16 chemicals used in this work, the masking scores did not show statistical correlations with the real activities of substances in the testing container (Fig. 2 B). Therefore, it is interpreted that we could exclude a factor, the evaporation rate and/or the vapor pressure of the chemicals, which determines the access rate of volatile chemicals to the olfactory epithelium. In the cell experiments described above, such an access rate is not included in the experimental process.

Bottom Line: It is interpreted, however, that in the natural odorant response the Cl(Ca) is affected by the reduction of Ca2+ influx through the CNG channels as a secondary effect.We conclude that odorants regulate CNG level to express masking, and Cl(Ca) in the cilia carries out the signal amplification and reduction evenly spanning the entire cilia.The present findings may serve possible molecular architectures to design effective masking agents, targeting olfactory manipulation at the nano-scale ciliary membrane.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Frontier Biosciences, Osaka University, Osaka 560-8531, Japan.

ABSTRACT
Olfactory masking has been used to erase the unpleasant sensation in human cultures for a long period of history. Here, we show a positive correlation between the human masking and the odorant suppression of the transduction current through the cyclic nucleotide-gated (CNG) and Ca2+-activated Cl- (Cl(Ca)) channels. Channels in the olfactory cilia were activated with the cytoplasmic photolysis of caged compounds, and their sensitiveness to odorant suppression was measured with the whole cell patch clamp. When 16 different types of chemicals were applied to cells, cyclic AMP (cAMP)-induced responses (a mixture of CNG and Cl(Ca) currents) were suppressed widely with these substances, but with different sensitivities. Using the same chemicals, in parallel, we measured human olfactory masking with 6-rate scoring tests and saw a correlation coefficient of 0.81 with the channel block. Ringer's solution that was just preexposed to the odorant-containing air affected the cAMP-induced current of the single cell, suggesting that odorant suppression occurs after the evaporation and air/water partition of the odorant chemicals at the olfactory mucus. To investigate the contribution of Cl(Ca), the current was exclusively activated by using the ultraviolet photolysis of caged Ca, DM-nitrophen. With chemical stimuli, it was confirmed that Cl(Ca) channels were less sensitive to the odorant suppression. It is interpreted, however, that in the natural odorant response the Cl(Ca) is affected by the reduction of Ca2+ influx through the CNG channels as a secondary effect. Because the signal transmission between CNG and Cl(Ca) channels includes nonlinear signal-boosting process, CNG channel blockage leads to an amplified reduction in the net current. In addition, we mapped the distribution of the Cl(Ca) channel in living olfactory single cilium using a submicron local [Ca2+]i elevation with the laser photolysis. Cl(Ca) channels are expressed broadly along the cilia. We conclude that odorants regulate CNG level to express masking, and Cl(Ca) in the cilia carries out the signal amplification and reduction evenly spanning the entire cilia. The present findings may serve possible molecular architectures to design effective masking agents, targeting olfactory manipulation at the nano-scale ciliary membrane.

Show MeSH
Related in: MedlinePlus