Limits...
In situ tip-recordings found no evidence for an Orco-based ionotropic mechanism of pheromone-transduction in Manduca sexta.

Nolte A, Funk NW, Mukunda L, Gawalek P, Werckenthin A, Hansson BS, Wicher D, Stengl M - PLoS ONE (2013)

Bottom Line: Here, in tip-recordings from intact pheromone-sensitive sensilla, perfusion with the Orco agonist VUAA1 did not increase pheromone-responses within the first 1000 ms.We conclude that we find no evidence for an Orco-dependent ionotropic pheromone transduction cascade in M. sexta.Instead, in M. sexta Orco appears to be a slower, second messenger-dependent pacemaker channel which affects kinetics and threshold of pheromone-detection via changes of intracellular Ca(2+) baseline concentrations.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Physiology, University of Kassel, Kassel, Germany.

ABSTRACT
The mechanisms of insect odor transduction are still controversial. Insect odorant receptors (ORs) are 7TM receptors with inverted membrane topology. They colocalize with a conserved coreceptor (Orco) with chaperone and ion channel function. Some studies suggest that insects employ exclusively ionotropic odor transduction via OR-Orco heteromers. Other studies provide evidence for different metabotropic odor transduction cascades, which employ second messenger-gated ion channel families for odor transduction. The hawkmoth Manduca sexta is an established model organism for studies of insect olfaction, also due to the availability of the hawkmoth-specific pheromone blend with its main component bombykal. Previous patch-clamp studies on primary cell cultures of M. sexta olfactory receptor neurons provided evidence for a pheromone-dependent activation of a phospholipase Cβ. Pheromone application elicited a sequence of one rapid, apparently IP3-dependent, transient and two slower Ca(2+)-dependent inward currents. It remains unknown whether additionally an ionotropic pheromone-transduction mechanism is employed. If indeed an OR-Orco ion channel complex underlies an ionotropic mechanism, then Orco agonist-dependent opening of the OR-Orco channel pore should add up to pheromone-dependent opening of the pore. Here, in tip-recordings from intact pheromone-sensitive sensilla, perfusion with the Orco agonist VUAA1 did not increase pheromone-responses within the first 1000 ms. However, VUAA1 increased spontaneous activity of olfactory receptor neurons Zeitgebertime- and dose-dependently. We conclude that we find no evidence for an Orco-dependent ionotropic pheromone transduction cascade in M. sexta. Instead, in M. sexta Orco appears to be a slower, second messenger-dependent pacemaker channel which affects kinetics and threshold of pheromone-detection via changes of intracellular Ca(2+) baseline concentrations.

Show MeSH
VUAA1-dependent MsexOrco activation affects bursting pattern of background activity.Comparison of the beginning (0–20 min) and end (100–120 min) of long term recordings showed a decrease of the number of action potentials (APs) per burst (A,B) as well as the percentage of APs in bursts (C,D) in the presence of 100 µM VUAA1. Furthermore, MsexOrco-dependent effects were mostly Zeitgebertime-dependent. Significant differences are indicated by asterisks (n.s. = not significant; *P<0.05, **P<0.01, ***P<0.001; Mann-Whitney test).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3643954&req=5

pone-0062648-g005: VUAA1-dependent MsexOrco activation affects bursting pattern of background activity.Comparison of the beginning (0–20 min) and end (100–120 min) of long term recordings showed a decrease of the number of action potentials (APs) per burst (A,B) as well as the percentage of APs in bursts (C,D) in the presence of 100 µM VUAA1. Furthermore, MsexOrco-dependent effects were mostly Zeitgebertime-dependent. Significant differences are indicated by asterisks (n.s. = not significant; *P<0.05, **P<0.01, ***P<0.001; Mann-Whitney test).

Mentions: Additionally, we analyzed whether VUAA1 affects the bursting pattern in the background activity of the BAL-sensitive ORN. The percentage of APs belonging to bursts and the number of APs per burst were calculated (Fig. 5). In the beginning of the recordings both VUAA1 concentrations decreased the number of APs per burst except for 100 µM VUAA1 at rest. The percentage of APs in bursts was always decreased by VUAA1. Addition of 100 µM VUAA1 significantly decreased the number of APs per bursts as well as the percentage of APs in bursts over the time course.


In situ tip-recordings found no evidence for an Orco-based ionotropic mechanism of pheromone-transduction in Manduca sexta.

Nolte A, Funk NW, Mukunda L, Gawalek P, Werckenthin A, Hansson BS, Wicher D, Stengl M - PLoS ONE (2013)

VUAA1-dependent MsexOrco activation affects bursting pattern of background activity.Comparison of the beginning (0–20 min) and end (100–120 min) of long term recordings showed a decrease of the number of action potentials (APs) per burst (A,B) as well as the percentage of APs in bursts (C,D) in the presence of 100 µM VUAA1. Furthermore, MsexOrco-dependent effects were mostly Zeitgebertime-dependent. Significant differences are indicated by asterisks (n.s. = not significant; *P<0.05, **P<0.01, ***P<0.001; Mann-Whitney test).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3643954&req=5

pone-0062648-g005: VUAA1-dependent MsexOrco activation affects bursting pattern of background activity.Comparison of the beginning (0–20 min) and end (100–120 min) of long term recordings showed a decrease of the number of action potentials (APs) per burst (A,B) as well as the percentage of APs in bursts (C,D) in the presence of 100 µM VUAA1. Furthermore, MsexOrco-dependent effects were mostly Zeitgebertime-dependent. Significant differences are indicated by asterisks (n.s. = not significant; *P<0.05, **P<0.01, ***P<0.001; Mann-Whitney test).
Mentions: Additionally, we analyzed whether VUAA1 affects the bursting pattern in the background activity of the BAL-sensitive ORN. The percentage of APs belonging to bursts and the number of APs per burst were calculated (Fig. 5). In the beginning of the recordings both VUAA1 concentrations decreased the number of APs per burst except for 100 µM VUAA1 at rest. The percentage of APs in bursts was always decreased by VUAA1. Addition of 100 µM VUAA1 significantly decreased the number of APs per bursts as well as the percentage of APs in bursts over the time course.

Bottom Line: Here, in tip-recordings from intact pheromone-sensitive sensilla, perfusion with the Orco agonist VUAA1 did not increase pheromone-responses within the first 1000 ms.We conclude that we find no evidence for an Orco-dependent ionotropic pheromone transduction cascade in M. sexta.Instead, in M. sexta Orco appears to be a slower, second messenger-dependent pacemaker channel which affects kinetics and threshold of pheromone-detection via changes of intracellular Ca(2+) baseline concentrations.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Physiology, University of Kassel, Kassel, Germany.

ABSTRACT
The mechanisms of insect odor transduction are still controversial. Insect odorant receptors (ORs) are 7TM receptors with inverted membrane topology. They colocalize with a conserved coreceptor (Orco) with chaperone and ion channel function. Some studies suggest that insects employ exclusively ionotropic odor transduction via OR-Orco heteromers. Other studies provide evidence for different metabotropic odor transduction cascades, which employ second messenger-gated ion channel families for odor transduction. The hawkmoth Manduca sexta is an established model organism for studies of insect olfaction, also due to the availability of the hawkmoth-specific pheromone blend with its main component bombykal. Previous patch-clamp studies on primary cell cultures of M. sexta olfactory receptor neurons provided evidence for a pheromone-dependent activation of a phospholipase Cβ. Pheromone application elicited a sequence of one rapid, apparently IP3-dependent, transient and two slower Ca(2+)-dependent inward currents. It remains unknown whether additionally an ionotropic pheromone-transduction mechanism is employed. If indeed an OR-Orco ion channel complex underlies an ionotropic mechanism, then Orco agonist-dependent opening of the OR-Orco channel pore should add up to pheromone-dependent opening of the pore. Here, in tip-recordings from intact pheromone-sensitive sensilla, perfusion with the Orco agonist VUAA1 did not increase pheromone-responses within the first 1000 ms. However, VUAA1 increased spontaneous activity of olfactory receptor neurons Zeitgebertime- and dose-dependently. We conclude that we find no evidence for an Orco-dependent ionotropic pheromone transduction cascade in M. sexta. Instead, in M. sexta Orco appears to be a slower, second messenger-dependent pacemaker channel which affects kinetics and threshold of pheromone-detection via changes of intracellular Ca(2+) baseline concentrations.

Show MeSH