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Peripheral sensitisation of nociceptors via G-protein-dependent potentiation of mechanotransduction currents.

Lechner SG, Lewin GR - J. Physiol. (Lond.) (2009)

Bottom Line: Here we show that the algogens UTP and ATP potentiate mechanosensitive RA currents in peptidergic nociceptive DRG neurons and reduce thresholds for mechanically induced action potential firing in these neurones.Pharmacological characterisation suggests that this effect is mediated by the Gq-coupled P2Y(2) nucleotide receptor.Together our findings suggest that UTP sensitises a subpopulation of cutaneous C-fibre nociceptors via a previously undescribed G-protein-dependent potentiation of mechanically activated RA-type currents.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Max-Delbrück-Center for Molecular Medicine, Robert Rössle Str. 10, 3125 Berlin, Germany.

ABSTRACT
Mechanical stimuli impinging on the skin are converted into electrical signals by mechanically gated ion channels located at the peripheral nerve endings of dorsal root ganglion (DRG) neurons. Under inflammatory conditions sensory neurons are commonly sensitised to mechanical stimuli; a putative mechanism that may contribute to such sensitisation of sensory neurons is enhanced responsiveness of mechanotransduction ion channels. Here we show that the algogens UTP and ATP potentiate mechanosensitive RA currents in peptidergic nociceptive DRG neurons and reduce thresholds for mechanically induced action potential firing in these neurones. Pharmacological characterisation suggests that this effect is mediated by the Gq-coupled P2Y(2) nucleotide receptor. Moreover, using the in vitro skin nerve technique, we show that UTP also increases action potential firing rates in response to mechanical stimuli in a subpopulation of skin C-fibre nociceptors. Together our findings suggest that UTP sensitises a subpopulation of cutaneous C-fibre nociceptors via a previously undescribed G-protein-dependent potentiation of mechanically activated RA-type currents.

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UTP reduces mechanical thresholds for action potentialsA, mechanical thresholds for action potentials under control conditions were determined by applying increasing mechanical stimuli (left side/before break). Thresholds in the presence of UTP were determined by applying series of decreasing subthreshold mechanical stimuli (threshold-1, -2 steps etc.; highlighted in red). UTP was present as indicated. B, comparison of mean mechanical AP thresholds determined as described in A, under control conditions (white bar) with those in the presence of UTP (n= 7, **P < 0.01, Students paired t test). C, bars show the mean resting membrane potentials measured before each mechanical stimulus under control conditions (white arrowheads, A) and in the presence of UTP (red arrowheads, A). D, inset shows the stimulation protocol used to determine electrical AP thresholds. Brief current injections of increasing amplitude (starting from 30 pA in increments of 20 pA) were applied. Mean membrane potentials measured 5–1 ms before the AP were considered as the AP threshold. Results are summarised in the bar graph.
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fig04: UTP reduces mechanical thresholds for action potentialsA, mechanical thresholds for action potentials under control conditions were determined by applying increasing mechanical stimuli (left side/before break). Thresholds in the presence of UTP were determined by applying series of decreasing subthreshold mechanical stimuli (threshold-1, -2 steps etc.; highlighted in red). UTP was present as indicated. B, comparison of mean mechanical AP thresholds determined as described in A, under control conditions (white bar) with those in the presence of UTP (n= 7, **P < 0.01, Students paired t test). C, bars show the mean resting membrane potentials measured before each mechanical stimulus under control conditions (white arrowheads, A) and in the presence of UTP (red arrowheads, A). D, inset shows the stimulation protocol used to determine electrical AP thresholds. Brief current injections of increasing amplitude (starting from 30 pA in increments of 20 pA) were applied. Mean membrane potentials measured 5–1 ms before the AP were considered as the AP threshold. Results are summarised in the bar graph.

Mentions: We next tested whether potentiation of RA currents by UTP was sufficient to significantly alter mechanical thresholds for action potential (AP) generation in nociceptors. Therefore, the mechanical threshold for AP generation was determined by applying increasing mechanical stimuli in increments of 350 nm (= 1 step) in current-clamp mode. The same cell was superfused with UTP and sub-threshold stimuli (threshold-1 step, -2 steps, etc.) were tested for their ability to evoke an AP (Fig. 4A). Strikingly, UTP significantly reduced mechanical thresholds by ∼25% from 2.68 ± 0.17 μm to 2.04 ± 0.11 μm (n= 6, P < 0.01, Student's paired t test; Fig. 4B). P2Y receptors are well known to modulate voltage-gated ion channels in many types of neurones (Lechner & Boehm, 2004), and thus we tested whether the effects of UTP could be explained by modulation of the electrical excitability of nociceptors. In rat DRG neurones, UTP was previously shown to produce a slow onset, slowly developing depolarisation of the membrane in a subpopulation of small diameter nociceptors (Molliver et al. 2002). However, during the short applications of UTP used here (≤10 s), we noted no significant change in the resting membrane potentials (measured directly before each mechanical stimulation, indicated by arrowheads, Fig. 4A and D). We also observed that during the time course of RA current sensitisation the magnitude of current injection required to evoke an AP was not changed in the presence of UTP (Fig. 4D).


Peripheral sensitisation of nociceptors via G-protein-dependent potentiation of mechanotransduction currents.

Lechner SG, Lewin GR - J. Physiol. (Lond.) (2009)

UTP reduces mechanical thresholds for action potentialsA, mechanical thresholds for action potentials under control conditions were determined by applying increasing mechanical stimuli (left side/before break). Thresholds in the presence of UTP were determined by applying series of decreasing subthreshold mechanical stimuli (threshold-1, -2 steps etc.; highlighted in red). UTP was present as indicated. B, comparison of mean mechanical AP thresholds determined as described in A, under control conditions (white bar) with those in the presence of UTP (n= 7, **P < 0.01, Students paired t test). C, bars show the mean resting membrane potentials measured before each mechanical stimulus under control conditions (white arrowheads, A) and in the presence of UTP (red arrowheads, A). D, inset shows the stimulation protocol used to determine electrical AP thresholds. Brief current injections of increasing amplitude (starting from 30 pA in increments of 20 pA) were applied. Mean membrane potentials measured 5–1 ms before the AP were considered as the AP threshold. Results are summarised in the bar graph.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2742277&req=5

fig04: UTP reduces mechanical thresholds for action potentialsA, mechanical thresholds for action potentials under control conditions were determined by applying increasing mechanical stimuli (left side/before break). Thresholds in the presence of UTP were determined by applying series of decreasing subthreshold mechanical stimuli (threshold-1, -2 steps etc.; highlighted in red). UTP was present as indicated. B, comparison of mean mechanical AP thresholds determined as described in A, under control conditions (white bar) with those in the presence of UTP (n= 7, **P < 0.01, Students paired t test). C, bars show the mean resting membrane potentials measured before each mechanical stimulus under control conditions (white arrowheads, A) and in the presence of UTP (red arrowheads, A). D, inset shows the stimulation protocol used to determine electrical AP thresholds. Brief current injections of increasing amplitude (starting from 30 pA in increments of 20 pA) were applied. Mean membrane potentials measured 5–1 ms before the AP were considered as the AP threshold. Results are summarised in the bar graph.
Mentions: We next tested whether potentiation of RA currents by UTP was sufficient to significantly alter mechanical thresholds for action potential (AP) generation in nociceptors. Therefore, the mechanical threshold for AP generation was determined by applying increasing mechanical stimuli in increments of 350 nm (= 1 step) in current-clamp mode. The same cell was superfused with UTP and sub-threshold stimuli (threshold-1 step, -2 steps, etc.) were tested for their ability to evoke an AP (Fig. 4A). Strikingly, UTP significantly reduced mechanical thresholds by ∼25% from 2.68 ± 0.17 μm to 2.04 ± 0.11 μm (n= 6, P < 0.01, Student's paired t test; Fig. 4B). P2Y receptors are well known to modulate voltage-gated ion channels in many types of neurones (Lechner & Boehm, 2004), and thus we tested whether the effects of UTP could be explained by modulation of the electrical excitability of nociceptors. In rat DRG neurones, UTP was previously shown to produce a slow onset, slowly developing depolarisation of the membrane in a subpopulation of small diameter nociceptors (Molliver et al. 2002). However, during the short applications of UTP used here (≤10 s), we noted no significant change in the resting membrane potentials (measured directly before each mechanical stimulation, indicated by arrowheads, Fig. 4A and D). We also observed that during the time course of RA current sensitisation the magnitude of current injection required to evoke an AP was not changed in the presence of UTP (Fig. 4D).

Bottom Line: Here we show that the algogens UTP and ATP potentiate mechanosensitive RA currents in peptidergic nociceptive DRG neurons and reduce thresholds for mechanically induced action potential firing in these neurones.Pharmacological characterisation suggests that this effect is mediated by the Gq-coupled P2Y(2) nucleotide receptor.Together our findings suggest that UTP sensitises a subpopulation of cutaneous C-fibre nociceptors via a previously undescribed G-protein-dependent potentiation of mechanically activated RA-type currents.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, Max-Delbrück-Center for Molecular Medicine, Robert Rössle Str. 10, 3125 Berlin, Germany.

ABSTRACT
Mechanical stimuli impinging on the skin are converted into electrical signals by mechanically gated ion channels located at the peripheral nerve endings of dorsal root ganglion (DRG) neurons. Under inflammatory conditions sensory neurons are commonly sensitised to mechanical stimuli; a putative mechanism that may contribute to such sensitisation of sensory neurons is enhanced responsiveness of mechanotransduction ion channels. Here we show that the algogens UTP and ATP potentiate mechanosensitive RA currents in peptidergic nociceptive DRG neurons and reduce thresholds for mechanically induced action potential firing in these neurones. Pharmacological characterisation suggests that this effect is mediated by the Gq-coupled P2Y(2) nucleotide receptor. Moreover, using the in vitro skin nerve technique, we show that UTP also increases action potential firing rates in response to mechanical stimuli in a subpopulation of skin C-fibre nociceptors. Together our findings suggest that UTP sensitises a subpopulation of cutaneous C-fibre nociceptors via a previously undescribed G-protein-dependent potentiation of mechanically activated RA-type currents.

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