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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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Lower doses of GRO/KC do not increase Na+ current density. Current densities were measured as in Figure 1, after overnight exposure to the indicated concentration of GRO/KC. For each concentration tested, data have been normalized to the control values obtained in cells from the same cultures with no GRO/KC treatment. *, significantly different from control. TTX-R current at 0 mV was used for this analysis. N = 27 cells for 0.06 nM dose (plus 17 control cells from the same cultures); 10 cells for 0.28 nM dose (plus 14 control cells), and 54 cells for 1.5 nM dose (plus 53 control cells).
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Figure 4: Lower doses of GRO/KC do not increase Na+ current density. Current densities were measured as in Figure 1, after overnight exposure to the indicated concentration of GRO/KC. For each concentration tested, data have been normalized to the control values obtained in cells from the same cultures with no GRO/KC treatment. *, significantly different from control. TTX-R current at 0 mV was used for this analysis. N = 27 cells for 0.06 nM dose (plus 17 control cells from the same cultures); 10 cells for 0.28 nM dose (plus 14 control cells), and 54 cells for 1.5 nM dose (plus 53 control cells).

Mentions: Lower doses of GRO/KC were also tested in similar experiments. Figure 4 shows the Na+ current density measured at two lower doses of GRO/KC, 0.28 and 0.06 nM. As shown, only the highest dose tested, 1.5 nM, gave a significant increase over control values, In Figure 4, data from control cells were obtained for the experiments at each separate dose. However, similar results were obtained if the data were analyzed by comparing current densities at each individual dose to the combined control values.


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)

Lower doses of GRO/KC do not increase Na+ current density. Current densities were measured as in Figure 1, after overnight exposure to the indicated concentration of GRO/KC. For each concentration tested, data have been normalized to the control values obtained in cells from the same cultures with no GRO/KC treatment. *, significantly different from control. TTX-R current at 0 mV was used for this analysis. N = 27 cells for 0.06 nM dose (plus 17 control cells from the same cultures); 10 cells for 0.28 nM dose (plus 14 control cells), and 54 cells for 1.5 nM dose (plus 53 control cells).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Lower doses of GRO/KC do not increase Na+ current density. Current densities were measured as in Figure 1, after overnight exposure to the indicated concentration of GRO/KC. For each concentration tested, data have been normalized to the control values obtained in cells from the same cultures with no GRO/KC treatment. *, significantly different from control. TTX-R current at 0 mV was used for this analysis. N = 27 cells for 0.06 nM dose (plus 17 control cells from the same cultures); 10 cells for 0.28 nM dose (plus 14 control cells), and 54 cells for 1.5 nM dose (plus 53 control cells).
Mentions: Lower doses of GRO/KC were also tested in similar experiments. Figure 4 shows the Na+ current density measured at two lower doses of GRO/KC, 0.28 and 0.06 nM. As shown, only the highest dose tested, 1.5 nM, gave a significant increase over control values, In Figure 4, data from control cells were obtained for the experiments at each separate dose. However, similar results were obtained if the data were analyzed by comparing current densities at each individual dose to the combined control values.

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