Reopening of ATP-sensitive potassium channels reduces neuropathic pain and regulates astroglial gap junctions in the rat spinal cord.

Department of Neurobiology, Parker University Research Institute, Dallas, TX 75229, USA.
Pain (Impact Factor: 5.64). 09/2011; 152(11):2605-15. DOI: 10.1016/j.pain.2011.08.003
Source: PubMed

ABSTRACT Adenosine triphosphate-sensitive potassium (K(ATP)) channels are suggested to be involved in pathogenesis of neuropathic pain, but remain underinvestigated in primary afferents and in the spinal cord. We examined alterations of K(ATP) channels in rat spinal cord and tested whether and how they could contribute to neuropathic pain. The results showed that protein expression for K(ATP) channel subunits SUR1, SUR2, and Kir6.1, but not Kir6.2, were significantly downregulated and associated with thermal hyperalgesia and mechanical allodynia after sciatic nerve injury. Spinal administration of a K(ATP) channel opener cromakalim (CRO, 5, 10, and 20 μg, respectively) prevented or suppressed, in a dose-dependent manner, the hyperalgesia and allodynia. Nerve injury also significantly increased expression and phosphorylation of connexin 43, an astroglial gap junction protein. Such an increase of phosphorylation of connexin 43 was inhibited by CRO treatment. Furthermore, preadministration of an astroglial gap junction decoupler carbenoxolone (10 μg) completely reversed the inhibitory effects of CRO treatment on the hyperalgesia and allodynia and phosphorylation of NR1 and NR2B receptors and the subsequent activation of Ca(2+)-dependent signals Ca(2+)/calmodulin-dependent kinase II and cyclic adenosine monophosphate (cAMP) response element binding protein. These findings suggest that nerve injury-induced downregulation of the K(ATP) channels in the spinal cord may interrupt the astroglial gap junctional function and contribute to neuropathic pain, thus the K(ATP) channels opener can reduce neuropathic pain probably partly via regulating the astroglial gap junctions. This study may provide a new strategy for treating neuropathic pain using K(ATP) channel openers in the clinic.

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    ABSTRACT: Accumulating evidence suggests that spinal cord astrocytes play an important role in neuropathic pain sensitization by releasing astrocytic mediators (e.g. cytokines, chemokines and growth factors). However, it remains unclear how astrocytes control the release of astrocytic mediators and sustain late-phase neuropathic pain. Astrocytic connexin-43 (now known as GJ1) has been implicated in gap junction and hemichannel communication of cytosolic contents through the glial syncytia and to the extracellular space, respectively. Connexin-43 also plays an essential role in facilitating the development of neuropathic pain, yet the mechanism for this contribution remains unknown. In this study, we investigated whether nerve injury could upregulate connexin-43 to sustain late-phase neuropathic pain by releasing chemokine from spinal astrocytes. Chronic constriction injury elicited a persistent upregulation of connexin-43 in spinal astrocytes for >3 weeks. Spinal (intrathecal) injection of carbenoxolone (a non-selective hemichannel blocker) and selective connexin-43 blockers (connexin-43 mimetic peptides (43)Gap26 and (37,43)Gap27), as well as astroglial toxin but not microglial inhibitors, given 3 weeks after nerve injury, effectively reduced mechanical allodynia, a cardinal feature of late-phase neuropathic pain. In cultured astrocytes, TNF-α elicited marked release of the chemokine CXCL1, and the release was blocked by carbenoxolone, Gap26/Gap27, and connexin-43 small interfering RNA. TNF-α also increased connexin-43 expression and hemichannel activity, but not gap junction communication in astrocyte cultures prepared from cortices and spinal cords. Spinal injection of TNF-α-activated astrocytes was sufficient to induce persistent mechanical allodynia, and this allodynia was suppressed by CXCL1 neutralization, CXCL1 receptor (CXCR2) antagonist, and pretreatment of astrocytes with connexin-43 small interfering RNA. Furthermore, nerve injury persistently increased excitatory synaptic transmission (spontaneous excitatory postsynaptic currents) in spinal lamina IIo nociceptive synapses in the late phase, and this increase was suppressed by carbenoxolone and Gap27, and recapitulated by CXCL1. Together, our findings demonstrate a novel mechanism of astrocytic connexin-43 to enhance spinal cord synaptic transmission and maintain neuropathic pain in the late-phase via releasing chemokines.
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    ABSTRACT: We have recently shown that adenosine-triphosphate-sensitive potassium [K(+)(ATP)] channel protein subunit, Kir6.1 is a phosphospecific interaction partner of the gap-junction protein connexin43 (Cx43). Since, both Cx43 and K(+)(ATP) are known to be involved in cell survial during hypoxia, we addressed the question, whether the interaction between Cx43 and K(+)(ATP) has a role in protecting cell against hypoxia-induced cell death. We report here that the Kir6.1 protein interacts, in a phosphospecific manner with Cx43 in the mitochondria of cardiomyocytic cell line H9C2. The hypoxia for 12-hours resulted in the appreciable increase in the phosphorylation at the serine 262 (S262) of the Cx43 with the concomitant increase in the Cx43 and Kir6.1 interaction. Moreover, the increased interaction was mediated by a signalling pathway involving PKC and more specifically by PKC epsilon. Functional implications of the association between the Cx43 and Kir6.1 was found to prevent mitochondria mediated hypoxia induced cell apoptosis. Our results demonstrate that PKC epsilon regulate the interaction between Cx43 and Kir6.1 in the cardiomyocyte mitochondria and this interaction prevents hypoxia induced cell death. Our results provide an interesting lead in developing effective strategies to protect cardiomyocytes from hypoxia/ischemia induced cell death.
    Cellular Signalling 05/2014; · 4.47 Impact Factor
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Jun 5, 2014