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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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Responses induced by caged Ca and caged cAMP. (A) Schema of caged Ca-induced current response. The response is caused by bypassing the receptor to CNG level. (B) Change in the current amplitude and prolongation of the falling phase after the establishment of WC recording configuration. The currents were obtained after WC in 2 (black), 3 (red), 4 (green), 5 (blue), 10 (light blue), and 15 (pink) min, respectively. Downward deflection of the upper trace indicates the timing and duration of the light stimulation. Vh = −50 mV. Light intensity was 0.48. (C) Change of the current amplitudes after WC. Plots indicate the mean, and the error bars show the SD. Numbers in parentheses indicate the number of examined cells. Red smooth line was drawn by the Hill fittings with Hill coefficient (nH) = 1.6, K1/2 = 4.4 min, and Imax = 101.6 pA. (D) Time course of the caged Ca-induced current response. Curve fitting was made with the single-exponential function (red, rising phase of the caged Ca-induced current was fitted by the Hill function [red] with nH of 1.6). Light stimulation was 0.48. (E) Responses induced by caged cAMP. Light stimulation was 0.48. (F) Comparison of response amplitudes induced by caged Ca and caged cAMP. There was a statistical significance with t test (P < 0.05). Numbers in parentheses indicate the numbers of cells examined. Vh = −50 mV.
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fig4: Responses induced by caged Ca and caged cAMP. (A) Schema of caged Ca-induced current response. The response is caused by bypassing the receptor to CNG level. (B) Change in the current amplitude and prolongation of the falling phase after the establishment of WC recording configuration. The currents were obtained after WC in 2 (black), 3 (red), 4 (green), 5 (blue), 10 (light blue), and 15 (pink) min, respectively. Downward deflection of the upper trace indicates the timing and duration of the light stimulation. Vh = −50 mV. Light intensity was 0.48. (C) Change of the current amplitudes after WC. Plots indicate the mean, and the error bars show the SD. Numbers in parentheses indicate the number of examined cells. Red smooth line was drawn by the Hill fittings with Hill coefficient (nH) = 1.6, K1/2 = 4.4 min, and Imax = 101.6 pA. (D) Time course of the caged Ca-induced current response. Curve fitting was made with the single-exponential function (red, rising phase of the caged Ca-induced current was fitted by the Hill function [red] with nH of 1.6). Light stimulation was 0.48. (E) Responses induced by caged cAMP. Light stimulation was 0.48. (F) Comparison of response amplitudes induced by caged Ca and caged cAMP. There was a statistical significance with t test (P < 0.05). Numbers in parentheses indicate the numbers of cells examined. Vh = −50 mV.

Mentions: Here, we examined 16 different volatile chemicals (Table I, for comparison with human tests) from an effect on the cAMP-induced response of single ORCs (Fig. 1 A). Fig. 1 (B and C) show cell responses induced by the increase of intraciliary cAMP by the UV photolysis of caged compound and the effects of chemicals on the cAMP-induced response. The current was monotonically inward at the holding membrane potential (Vh) of −50 mV. It has been shown that the cAMP-induced response in olfactory cilia is actually a mixture of currents through the CNG and Cl(Ca) channels (Kleene, 1993; Kurahashi and Yau, 1993; Lowe and Gold, 1993). When benzyl acetate was applied to the cell during the response, the current was almost completely abolished (Fig. 1 B). The time course of the response reduction was fast (<1 s, not depicted; see Fig. 4 of Chen et al., 2006), especially when compared with that obtained for CNG channels expressed in oocytes (Chen et al., 2006).


Mechanism of olfactory masking in the sensory cilia.

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

Responses induced by caged Ca and caged cAMP. (A) Schema of caged Ca-induced current response. The response is caused by bypassing the receptor to CNG level. (B) Change in the current amplitude and prolongation of the falling phase after the establishment of WC recording configuration. The currents were obtained after WC in 2 (black), 3 (red), 4 (green), 5 (blue), 10 (light blue), and 15 (pink) min, respectively. Downward deflection of the upper trace indicates the timing and duration of the light stimulation. Vh = −50 mV. Light intensity was 0.48. (C) Change of the current amplitudes after WC. Plots indicate the mean, and the error bars show the SD. Numbers in parentheses indicate the number of examined cells. Red smooth line was drawn by the Hill fittings with Hill coefficient (nH) = 1.6, K1/2 = 4.4 min, and Imax = 101.6 pA. (D) Time course of the caged Ca-induced current response. Curve fitting was made with the single-exponential function (red, rising phase of the caged Ca-induced current was fitted by the Hill function [red] with nH of 1.6). Light stimulation was 0.48. (E) Responses induced by caged cAMP. Light stimulation was 0.48. (F) Comparison of response amplitudes induced by caged Ca and caged cAMP. There was a statistical significance with t test (P < 0.05). Numbers in parentheses indicate the numbers of cells examined. Vh = −50 mV.
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fig4: Responses induced by caged Ca and caged cAMP. (A) Schema of caged Ca-induced current response. The response is caused by bypassing the receptor to CNG level. (B) Change in the current amplitude and prolongation of the falling phase after the establishment of WC recording configuration. The currents were obtained after WC in 2 (black), 3 (red), 4 (green), 5 (blue), 10 (light blue), and 15 (pink) min, respectively. Downward deflection of the upper trace indicates the timing and duration of the light stimulation. Vh = −50 mV. Light intensity was 0.48. (C) Change of the current amplitudes after WC. Plots indicate the mean, and the error bars show the SD. Numbers in parentheses indicate the number of examined cells. Red smooth line was drawn by the Hill fittings with Hill coefficient (nH) = 1.6, K1/2 = 4.4 min, and Imax = 101.6 pA. (D) Time course of the caged Ca-induced current response. Curve fitting was made with the single-exponential function (red, rising phase of the caged Ca-induced current was fitted by the Hill function [red] with nH of 1.6). Light stimulation was 0.48. (E) Responses induced by caged cAMP. Light stimulation was 0.48. (F) Comparison of response amplitudes induced by caged Ca and caged cAMP. There was a statistical significance with t test (P < 0.05). Numbers in parentheses indicate the numbers of cells examined. Vh = −50 mV.
Mentions: Here, we examined 16 different volatile chemicals (Table I, for comparison with human tests) from an effect on the cAMP-induced response of single ORCs (Fig. 1 A). Fig. 1 (B and C) show cell responses induced by the increase of intraciliary cAMP by the UV photolysis of caged compound and the effects of chemicals on the cAMP-induced response. The current was monotonically inward at the holding membrane potential (Vh) of −50 mV. It has been shown that the cAMP-induced response in olfactory cilia is actually a mixture of currents through the CNG and Cl(Ca) channels (Kleene, 1993; Kurahashi and Yau, 1993; Lowe and Gold, 1993). When benzyl acetate was applied to the cell during the response, the current was almost completely abolished (Fig. 1 B). The time course of the response reduction was fast (<1 s, not depicted; see Fig. 4 of Chen et al., 2006), especially when compared with that obtained for CNG channels expressed in oocytes (Chen et al., 2006).

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