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NF-kappaB mediated enhancement of potassium currents by the chemokine CXCL1/growth related oncogene in small diameter rat sensory neurons.

Yang RH, Strong JA, Zhang JM - Mol Pain (2009)

Bottom Line: We examined the direct effects of GRO/KC on small diameter DRG neurons, which are predominantly nociceptive.The amplitude of the fast inactivating component increased significantly with no large shifts in the voltage dependence of inactivation.The results suggest that GRO/KC has important effects in inflammatory processes via its direct actions on sensory neurons, and that activation of NF-kappaB is involved in the GRO/KC-induced enhancement of K currents.

View Article: PubMed Central - HTML - PubMed

Affiliation: Pain Research Center, Department of Anesthesiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0531, USA. Rui-Hua.Yang@uc.edu

ABSTRACT

Background: Inflammatory processes play important roles in both neuropathic and inflammatory pain states, but the effects of inflammation per se within the sensory ganglia are not well understood. The cytokine growth-related oncogene (GRO/KC; CXCL1) shows strong, rapid upregulation in dorsal root ganglion (DRG) in both nerve injury and inflammatory pain models. We examined the direct effects of GRO/KC on small diameter DRG neurons, which are predominantly nociceptive. Whole cell voltage clamp technique was used to measure voltage-activated potassium (K) currents in acutely cultured adult rat small diameter sensory neurons. Fluorescently labeled isolectin B4 (IB4) was used to classify cells as IB4-positive or IB4-negative.

Results: In IB4-negative neurons, voltage-activated K current densities of both transient and sustained components were increased after overnight incubation with GRO/KC (1.5 nM), without marked changes in voltage dependence or kinetics. The average values for the slow and fast decay time constants at 20 mV were unchanged by GRO/KC. The amplitude of the fast inactivating component increased significantly with no large shifts in the voltage dependence of inactivation. The increase in K currents was completely blocked by co-incubation with protein synthesis inhibitor cycloheximide (CHX) or NF-kappaB inhibitors pyrrolidine dithiocarbamate (PDTC) or quinazoline (6-Amino-4-(4-phenoxypheny lethylamino;QNZ). In contrast, the voltage-activated K current of IB4-positive neurons was unchanged by GRO/KC. GRO/KC incubation caused no significant changes in the expression level of eight selected voltage-gated K channel genes in quantitative PCR analysis.

Conclusion: The results suggest that GRO/KC has important effects in inflammatory processes via its direct actions on sensory neurons, and that activation of NF-kappaB is involved in the GRO/KC-induced enhancement of K currents.

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Inactivation time constants at +20 mV are not affected by GRO/KC incubation. The falling phase of the currents at a test pulse of +20 mV following prepulses between -100 and 0 mV was fitted with the sum of two exponentials. The time constants for the slow and fast components were not significantly changed by GRO/KC incubation.
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Figure 4: Inactivation time constants at +20 mV are not affected by GRO/KC incubation. The falling phase of the currents at a test pulse of +20 mV following prepulses between -100 and 0 mV was fitted with the sum of two exponentials. The time constants for the slow and fast components were not significantly changed by GRO/KC incubation.

Mentions: The voltage dependence of steady state inactivation was also determined for the voltage-activated K currents. The protocol consisted of a 1-s conditioning prepulse to potentials ranging between -100 and 0 mV followed by a voltage step to a +20 mV test pulse for 1 s. As in our previous study [18], the decay of the outward current at +20 mV could be well described in most cells as the sum of a sustained component and two exponentially decaying transient components whose time constants differed by an order of magnitude. The average values for the slow and fast time constants in IB4-negative cells were unchanged by GRO/KC (1100.1 ± 254 ms.1 vs. 861.3 ± 154.2 ms, and 62.4 ± 7.8 ms vs. 57.6 ± 4.8 ms, respectively; Figure 4). Fast and slow time constants in IB4-positive cells were also not significantly changed by GRO/KC incubation, and did not differ significantly from those observed in IB4-negative cells.


NF-kappaB mediated enhancement of potassium currents by the chemokine CXCL1/growth related oncogene in small diameter rat sensory neurons.

Yang RH, Strong JA, Zhang JM - Mol Pain (2009)

Inactivation time constants at +20 mV are not affected by GRO/KC incubation. The falling phase of the currents at a test pulse of +20 mV following prepulses between -100 and 0 mV was fitted with the sum of two exponentials. The time constants for the slow and fast components were not significantly changed by GRO/KC incubation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2698898&req=5

Figure 4: Inactivation time constants at +20 mV are not affected by GRO/KC incubation. The falling phase of the currents at a test pulse of +20 mV following prepulses between -100 and 0 mV was fitted with the sum of two exponentials. The time constants for the slow and fast components were not significantly changed by GRO/KC incubation.
Mentions: The voltage dependence of steady state inactivation was also determined for the voltage-activated K currents. The protocol consisted of a 1-s conditioning prepulse to potentials ranging between -100 and 0 mV followed by a voltage step to a +20 mV test pulse for 1 s. As in our previous study [18], the decay of the outward current at +20 mV could be well described in most cells as the sum of a sustained component and two exponentially decaying transient components whose time constants differed by an order of magnitude. The average values for the slow and fast time constants in IB4-negative cells were unchanged by GRO/KC (1100.1 ± 254 ms.1 vs. 861.3 ± 154.2 ms, and 62.4 ± 7.8 ms vs. 57.6 ± 4.8 ms, respectively; Figure 4). Fast and slow time constants in IB4-positive cells were also not significantly changed by GRO/KC incubation, and did not differ significantly from those observed in IB4-negative cells.

Bottom Line: We examined the direct effects of GRO/KC on small diameter DRG neurons, which are predominantly nociceptive.The amplitude of the fast inactivating component increased significantly with no large shifts in the voltage dependence of inactivation.The results suggest that GRO/KC has important effects in inflammatory processes via its direct actions on sensory neurons, and that activation of NF-kappaB is involved in the GRO/KC-induced enhancement of K currents.

View Article: PubMed Central - HTML - PubMed

Affiliation: Pain Research Center, Department of Anesthesiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0531, USA. Rui-Hua.Yang@uc.edu

ABSTRACT

Background: Inflammatory processes play important roles in both neuropathic and inflammatory pain states, but the effects of inflammation per se within the sensory ganglia are not well understood. The cytokine growth-related oncogene (GRO/KC; CXCL1) shows strong, rapid upregulation in dorsal root ganglion (DRG) in both nerve injury and inflammatory pain models. We examined the direct effects of GRO/KC on small diameter DRG neurons, which are predominantly nociceptive. Whole cell voltage clamp technique was used to measure voltage-activated potassium (K) currents in acutely cultured adult rat small diameter sensory neurons. Fluorescently labeled isolectin B4 (IB4) was used to classify cells as IB4-positive or IB4-negative.

Results: In IB4-negative neurons, voltage-activated K current densities of both transient and sustained components were increased after overnight incubation with GRO/KC (1.5 nM), without marked changes in voltage dependence or kinetics. The average values for the slow and fast decay time constants at 20 mV were unchanged by GRO/KC. The amplitude of the fast inactivating component increased significantly with no large shifts in the voltage dependence of inactivation. The increase in K currents was completely blocked by co-incubation with protein synthesis inhibitor cycloheximide (CHX) or NF-kappaB inhibitors pyrrolidine dithiocarbamate (PDTC) or quinazoline (6-Amino-4-(4-phenoxypheny lethylamino;QNZ). In contrast, the voltage-activated K current of IB4-positive neurons was unchanged by GRO/KC. GRO/KC incubation caused no significant changes in the expression level of eight selected voltage-gated K channel genes in quantitative PCR analysis.

Conclusion: The results suggest that GRO/KC has important effects in inflammatory processes via its direct actions on sensory neurons, and that activation of NF-kappaB is involved in the GRO/KC-induced enhancement of K currents.

Show MeSH
Related in: MedlinePlus