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The chemokine CXCL1/growth related oncogene increases sodium currents and neuronal excitability in small diameter sensory neurons.

Wang JG, Strong JA, Xie W, Yang RH, Coyle DE, Wick DM, Dorsey ED, Zhang JM - Mol Pain (2008)

Bottom Line: These effects required long exposures, and were completely blocked by co-incubation with protein synthesis inhibitor cycloheximide.Many studies on the role of chemokines in pain conditions have focused on their rapid and indirect effects on neurons, via release of inflammatory mediators from immune and glial cells.Our study suggests that GRO/KC may also have important pro-nociceptive effects via its direct actions on sensory neurons, and may induce long-term changes that involve protein synthesis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anesthesiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0531, USA. jungang.wang@uchsc.edu

ABSTRACT

Background: Altered Na+ channel expression, enhanced excitability, and spontaneous activity occur in nerve-injury and inflammatory models of pathological pain, through poorly understood mechanisms. The cytokine GRO/KC (growth related oncogene; CXCL1) shows strong, rapid upregulation in dorsal root ganglion in both nerve injury and inflammatory models. Neurons and glia express its receptor (CXCR2). CXCL1 has well-known effects on immune cells, but little is known about its direct effects on neurons.

Results: We report that GRO/KC incubation (1.5 nM, overnight) caused marked upregulation of Na+ currents in acutely isolated small diameter rat (adult) sensory neurons in vitro. In both IB4-positive and IB4-negative sensory neurons, TTX-resistant and TTX-sensitive currents increased 2- to 4 fold, without altered voltage dependence or kinetic changes. These effects required long exposures, and were completely blocked by co-incubation with protein synthesis inhibitor cycloheximide. Amplification of cDNA from the neuronal cultures showed that 3 Na channel isoforms were predominant both before and after GRO/KC treatment (Nav 1.1, 1.7, and 1.8). TTX-sensitive isoforms 1.1 and 1.7 significantly increased 2 - 3 fold after GRO/KC incubation, while 1.8 showed a trend towards increased expression. Current clamp experiments showed that GRO/KC caused a marked increase in excitability, including resting potential depolarization, decreased rheobase, and lower action potential threshold. Neurons acquired a striking ability to fire repetitively; IB4-positive cells also showed marked broadening of action potentials. Immunohistochemical labelling confirmed that the CXCR2 receptor was present in most neurons both in dissociated cells and in DRG sections, as previously shown for neurons in the CNS.

Conclusion: Many studies on the role of chemokines in pain conditions have focused on their rapid and indirect effects on neurons, via release of inflammatory mediators from immune and glial cells. Our study suggests that GRO/KC may also have important pro-nociceptive effects via its direct actions on sensory neurons, and may induce long-term changes that involve protein synthesis.

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Small diameter neurons acquire the ability to fire repetitively after GRO/KC incubation. A, Examples of the voltage response to a 90 pA 1 second current injection in a control IB4-negative neuron (top) and in an IB4-negative neuron incubated overnight in GRO/KC (1.5 nM) (bottom). B. Examples of the voltage response to a 50 pA current injection in control (top) and GRO/KC incubated (bottom) IB4-positive neurons. Same scale as A. C, D: Average number of action potentials during a 1 second current injection as a function of current amplitude in IB4-negative (C) and IB4-positive (D) cells. *, significant difference between GRO/KC and control cells at the indicated current value (two-way RM ANOVA with Holm-Sidak post test). N = 8 to 14 cells per group; data combined from 3 different cultures.
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Figure 7: Small diameter neurons acquire the ability to fire repetitively after GRO/KC incubation. A, Examples of the voltage response to a 90 pA 1 second current injection in a control IB4-negative neuron (top) and in an IB4-negative neuron incubated overnight in GRO/KC (1.5 nM) (bottom). B. Examples of the voltage response to a 50 pA current injection in control (top) and GRO/KC incubated (bottom) IB4-positive neurons. Same scale as A. C, D: Average number of action potentials during a 1 second current injection as a function of current amplitude in IB4-negative (C) and IB4-positive (D) cells. *, significant difference between GRO/KC and control cells at the indicated current value (two-way RM ANOVA with Holm-Sidak post test). N = 8 to 14 cells per group; data combined from 3 different cultures.

Mentions: Initially, the experiments shown in Table 2 were conducted by injecting short-duration (80 msec) current pulses, and it was evident that after GRO/KC incubation many cells fired action potentials for the entire duration of these short depolarizing pulses. In order to examine this effect in more detail, subsequent experiments were conducted using much longer (1 s) current pulses. As shown in Figure 7, such long pulses demonstrated a striking ability for repetitive firing that developed after GRO/KC incubation. In IB4-negative cells, multiple action potentials (up to 27) could be observed during the 1 second current injection, and these lasted throughout the entire pulse. IB4-positive cells also acquired the ability to fire throughout the 1 second current injection after GRO/KC incubation. In this case the number of action potentials per pulse did not increase as dramatically; rather, the action potentials tended to become very broad (Figure 7B and Table 2), though still continuing until the end of the 1 second current injection. The significant increase in action potential width (68%) seen in IB4-positive cells in Table 2 may be a conservative estimate, because those measurements are from the first evoked action potential and action potentials tended to broaden even more during the course of a long depolarizing pulse (Figure 7B).


The chemokine CXCL1/growth related oncogene increases sodium currents and neuronal excitability in small diameter sensory neurons.

Wang JG, Strong JA, Xie W, Yang RH, Coyle DE, Wick DM, Dorsey ED, Zhang JM - Mol Pain (2008)

Small diameter neurons acquire the ability to fire repetitively after GRO/KC incubation. A, Examples of the voltage response to a 90 pA 1 second current injection in a control IB4-negative neuron (top) and in an IB4-negative neuron incubated overnight in GRO/KC (1.5 nM) (bottom). B. Examples of the voltage response to a 50 pA current injection in control (top) and GRO/KC incubated (bottom) IB4-positive neurons. Same scale as A. C, D: Average number of action potentials during a 1 second current injection as a function of current amplitude in IB4-negative (C) and IB4-positive (D) cells. *, significant difference between GRO/KC and control cells at the indicated current value (two-way RM ANOVA with Holm-Sidak post test). N = 8 to 14 cells per group; data combined from 3 different cultures.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2562993&req=5

Figure 7: Small diameter neurons acquire the ability to fire repetitively after GRO/KC incubation. A, Examples of the voltage response to a 90 pA 1 second current injection in a control IB4-negative neuron (top) and in an IB4-negative neuron incubated overnight in GRO/KC (1.5 nM) (bottom). B. Examples of the voltage response to a 50 pA current injection in control (top) and GRO/KC incubated (bottom) IB4-positive neurons. Same scale as A. C, D: Average number of action potentials during a 1 second current injection as a function of current amplitude in IB4-negative (C) and IB4-positive (D) cells. *, significant difference between GRO/KC and control cells at the indicated current value (two-way RM ANOVA with Holm-Sidak post test). N = 8 to 14 cells per group; data combined from 3 different cultures.
Mentions: Initially, the experiments shown in Table 2 were conducted by injecting short-duration (80 msec) current pulses, and it was evident that after GRO/KC incubation many cells fired action potentials for the entire duration of these short depolarizing pulses. In order to examine this effect in more detail, subsequent experiments were conducted using much longer (1 s) current pulses. As shown in Figure 7, such long pulses demonstrated a striking ability for repetitive firing that developed after GRO/KC incubation. In IB4-negative cells, multiple action potentials (up to 27) could be observed during the 1 second current injection, and these lasted throughout the entire pulse. IB4-positive cells also acquired the ability to fire throughout the 1 second current injection after GRO/KC incubation. In this case the number of action potentials per pulse did not increase as dramatically; rather, the action potentials tended to become very broad (Figure 7B and Table 2), though still continuing until the end of the 1 second current injection. The significant increase in action potential width (68%) seen in IB4-positive cells in Table 2 may be a conservative estimate, because those measurements are from the first evoked action potential and action potentials tended to broaden even more during the course of a long depolarizing pulse (Figure 7B).

Bottom Line: These effects required long exposures, and were completely blocked by co-incubation with protein synthesis inhibitor cycloheximide.Many studies on the role of chemokines in pain conditions have focused on their rapid and indirect effects on neurons, via release of inflammatory mediators from immune and glial cells.Our study suggests that GRO/KC may also have important pro-nociceptive effects via its direct actions on sensory neurons, and may induce long-term changes that involve protein synthesis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anesthesiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0531, USA. jungang.wang@uchsc.edu

ABSTRACT

Background: Altered Na+ channel expression, enhanced excitability, and spontaneous activity occur in nerve-injury and inflammatory models of pathological pain, through poorly understood mechanisms. The cytokine GRO/KC (growth related oncogene; CXCL1) shows strong, rapid upregulation in dorsal root ganglion in both nerve injury and inflammatory models. Neurons and glia express its receptor (CXCR2). CXCL1 has well-known effects on immune cells, but little is known about its direct effects on neurons.

Results: We report that GRO/KC incubation (1.5 nM, overnight) caused marked upregulation of Na+ currents in acutely isolated small diameter rat (adult) sensory neurons in vitro. In both IB4-positive and IB4-negative sensory neurons, TTX-resistant and TTX-sensitive currents increased 2- to 4 fold, without altered voltage dependence or kinetic changes. These effects required long exposures, and were completely blocked by co-incubation with protein synthesis inhibitor cycloheximide. Amplification of cDNA from the neuronal cultures showed that 3 Na channel isoforms were predominant both before and after GRO/KC treatment (Nav 1.1, 1.7, and 1.8). TTX-sensitive isoforms 1.1 and 1.7 significantly increased 2 - 3 fold after GRO/KC incubation, while 1.8 showed a trend towards increased expression. Current clamp experiments showed that GRO/KC caused a marked increase in excitability, including resting potential depolarization, decreased rheobase, and lower action potential threshold. Neurons acquired a striking ability to fire repetitively; IB4-positive cells also showed marked broadening of action potentials. Immunohistochemical labelling confirmed that the CXCR2 receptor was present in most neurons both in dissociated cells and in DRG sections, as previously shown for neurons in the CNS.

Conclusion: Many studies on the role of chemokines in pain conditions have focused on their rapid and indirect effects on neurons, via release of inflammatory mediators from immune and glial cells. Our study suggests that GRO/KC may also have important pro-nociceptive effects via its direct actions on sensory neurons, and may induce long-term changes that involve protein synthesis.

Show MeSH
Related in: MedlinePlus