Modulation of chloride homeostasis by inflammatory mediators in dorsal root ganglion neurons

• Main Authors: Möhrlen Frank (Author), Gensch Thomas (Author), Franjic-Würtz Christina (Author), Woitecki Anne (Author), Funk Katharina (Author), Frings Stephan (Author)
• Format: Book
• Published: SAGE Publishing, 2008-08-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.

Summary

<p>Abstract</p> <p>Background</p> <p>Chloride currents in peripheral nociceptive neurons have been implicated in the generation of afferent nociceptive signals, as Cl^-accumulation in sensory endings establishes the driving force for depolarizing, and even excitatory, Cl^-currents. The intracellular Cl^-concentration can, however, vary considerably between individual DRG neurons. This raises the question, whether the contribution of Cl^-currents to signal generation differs between individual afferent neurons, and whether the specific Cl^-levels in these neurons are subject to modulation. Based on the hypothesis that modulation of the peripheral Cl^-homeostasis is involved in the generation of inflammatory hyperalgesia, we examined the effects of inflammatory mediators on intracellular Cl^-concentrations and on the expression levels of Cl^-transporters in rat DRG neurons.</p> <p>Results</p> <p>We developed an <it>in vitro </it>assay for testing how inflammatory mediators influence Cl^-concentration and the expression of Cl^-transporters. Intact DRGs were treated with 100 ng/ml NGF, 1.8 μM ATP, 0.9 μM bradykinin, and 1.4 μM PGE₂for 1-3 hours. Two-photon fluorescence lifetime imaging with the Cl^--sensitive dye MQAE revealed an increase of the intracellular Cl^-concentration within 2 hours of treatment. This effect coincided with enhanced phosphorylation of the Na⁺-K⁺-2Cl^-cotransporter NKCC1, suggesting that an increased activity of that transporter caused the early rise of intracellular Cl^-levels. Immunohistochemistry of NKCC1 and KCC2, the main neuronal Cl^-importer and exporter, respectively, exposed an inverse regulation by the inflammatory mediators. While the NKCC1 immunosignal increased, that of KCC2 declined after 3 hours of treatment. In contrast, the mRNA levels of the two transporters did not change markedly during this time. These data demonstrate a fundamental transition in Cl^-homeostasis toward a state of augmented Cl^-accumulation, which is induced by a 1-3 hour treatment with inflammatory mediators.</p> <p>Conclusion</p> <p>Our findings indicate that inflammatory mediators impact on Cl^-homeostasis in DRG neurons. Inflammatory mediators raise intracellular Cl^-levels and, hence, the driving force for depolarizing Cl^-efflux. These findings corroborate current concepts for the role of Cl^-regulation in the generation of inflammatory hyperalgesia and allodynia. As the intracellular Cl^-concentration rises in DRG neurons, afferent signals can be boosted by excitatory Cl^-currents in the presynaptic terminals. Moreover, excitatory Cl^-currents in peripheral sensory endings may also contribute to the generation or modulation of afferent signals, especially in inflamed tissue.</p>

Item Description

10.1186/1744-8069-4-32
1744-8069