Thompson RJ, Zhou N, MacVicar BAIschemia opens neuronal gap junction hemichannels. Science 312:924-927

Department of Psychiatry and Brain Research Centre, University of British Columbia, Vancouver, British Columbia V6T 2B5, Canada.
Science (Impact Factor: 33.61). 06/2006; 312(5775):924-7. DOI: 10.1126/science.1126241
Source: PubMed


Neuronal excitotoxicity during stroke is caused by activation of unidentified large-conductance channels, leading to swelling
and calcium dysregulation. We show that ischemic-like conditions [O2/glucose deprivation (OGD)] open hemichannels, or half gap junctions, in neurons. Hemichannel opening was indicated by a large
linear current and flux across the membrane of small fluorescent molecules. Single-channel openings of hemichannels (530 picosiemens)
were observed in OGD. Both the current and dye flux were blocked by inhibitors of hemichannels. Therefore, hemichannel opening
contributes to the profound ionic dysregulation during stroke and may be a ubiquitous component of ischemic neuronal death.

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Available from: Roger J Thompson
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    • "There is considerable evidence that pannexin (Px) and connexin (Cx) hemichannels exhibit stimulus-dependent opening and mediate influx and/or efflux transport of organic ions, including fluorescent dyes and endogenous signaling molecules, such as ATP and glutamate (Bargiotas et al., 2009; MacVicar and Thompson, 2010; Bosco et al., 2011). Thompson et al. (2006) proposed that the opening of Px1 in pyramidal neurons under ischemia-like oxygen/glucose deprivation conditions is a major contributor to the increased influx and efflux transport of sulforhodamine 101 (SR-101) and calcein, respectively. It has also been shown that: 1) Cx43 and Cx37 proteins are expressed in rat brain capillary endothelial RBE4 cells (De Bock et al., 2011), 2) mouse inner retina capillary endothelial cells show luminal localization of Px1 (Shestopalov and Panchin, 2008), and 3) the Cx43-and Cx37-mediated influx of propidium iodide (PI) is increased in RBE4 cells in the absence of extracellular Ca 21 (De Bock et al., 2011, 2012), which reflect the conditions in acute brain ischemia (Silver and Erecinska, 1990). "
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    ABSTRACT: Dysregulation of blood-brain barrier (BBB) transport function is considered to exacerbate neuronal damage in acute ischemic stroke. The purpose of this study was to clarify the characteristics of pannexin (Px) and/or connexin (Cx) hemichannel(s)-mediated transport of organic anions and cations in human BBB endothelial cell line hCMEC/D3 and to identify inhibitors of hemichannel opening in hCMEC/D3 cells in the absence of extracellular Ca(2+), a condition mimicking acute ischemic stroke. In the absence of extracellular Ca(2+), the cells showed increased uptake and efflux transport of organic ionic fluorescent dyes. Classical hemichannel inhibitors markedly inhibited the enhanced uptake and efflux. Quantitative targeted absolute proteomics confirmed Px1 and Cx43 protein expression in plasma membrane of hCMEC/D3 cells. Knock-down of Px1 and Cx43 with siRNAs significantly inhibited the enhanced uptake and efflux of organic anionic and cationic fluorescent dyes. Clinically used cilnidipine and progesterone, which have neuroprotective effects in animal ischemia models, were identified as inhibitors of hemichannel opening. These findings suggest that altered transport dynamics at the human BBB in the absence of extracellular Ca(2+) is at least partly due to opening of Px1 and Cx43 hemichannels. Therefore, we speculate that Px1 and Cx43 may be potential drug targets to ameliorate BBB transport dysregulation during acute ischemia. The American Society for Pharmacology and Experimental Therapeutics.
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    • "These toxic molecules are propagated from injured cells to healthier cells through gap junctions. Ischemic conditions also induce uncoupled hemichannels to open, leading to paracrine transfer of toxic molecules (Thompson et al., 2006; De Vuyst et al., 2007). These waves of death signals activate astrocytes and microglia, inducing the release of toxic molecules including glutamate, ROS, NO, and pro-inflammatory cytokines and chemokines. "
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    ABSTRACT: Microglia are macrophage-like resident immune cells that contribute to the maintenance of homeostasis in the central nervous system (CNS). Abnormal activation of microglia can cause damage in the CNS, and accumulation of activated microglia is a characteristic pathological observation in neurologic conditions such as trauma, stroke, inflammation, epilepsy, and neurodegenerative diseases. Activated microglia secrete high levels of glutamate, which damages CNS cells and has been implicated as a major cause of neurodegeneration in these conditions. Glutamate-receptor blockers and microglia inhibitors (e.g., minocycline) have been examined as therapeutic candidates for several neurodegenerative diseases; however, these compounds exerted little therapeutic benefit because they either perturbed physiological glutamate signals or suppressed the actions of protective microglia. The ideal therapeutic approach would hamper the deleterious roles of activated microglia without diminishing their protective effects. We recently found that abnormally activated microglia secrete glutamate via gap-junction hemichannels on the cell surface. Moreover, administration of gap-junction inhibitors significantly suppressed excessive microglial glutamate release and improved disease symptoms in animal models of neurologic conditions such as stroke, multiple sclerosis, amyotrophic lateral sclerosis, and Alzheimer's disease. Recent evidence also suggests that neuronal and glial communication via gap junctions amplifies neuroinflammation and neurodegeneration. Elucidation of the precise pathologic roles of gap junctions and hemichannels may lead to a novel therapeutic strategies that can slow and halt the progression of neurodegenerative diseases.
    Full-text · Article · Sep 2014 · Frontiers in Cellular Neuroscience
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    • "In neurons, panx1 has been observed in the postsynaptic density of hippocampal pyramidal cells in co-expression with the postsynaptic density 95 protein, suggesting a modulatory role in excitability of postsynaptic neurons [58]. At present, there is growing evidence that supports a role of panx1 channels in some pathologic conditions of the central nervous system, particularly in epilepsy, cerebral ischemia, and neuroinflammation [16] [44] [46] [50] [51]. Glutamate and adenosine triphosphatase (ATP) have been described as crucial molecules in acute pain signaling in the dorsal horn of the spinal cord, as well as in the process of developing and maintaining central sensitization underlying chronic pain [5] [7] [25] [30]. "
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    ABSTRACT: Pannexin 1 (panx1) is a large-pore membrane channel expressed in many tissues of mammals, including neurons and glial cells. Panx1 channels are highly permeable to calcium and ATP and, on the other hand, they can be opened by ATP and glutamate, two crucial molecules for acute and chronic pain signaling in the spinal cord dorsal horn, thus suggesting that panx1 could be a key component for the generation of central sensitization during persistent pain. In this study we examined the effect of three panx1 blockers, 10panx peptide, carbenoxolone and probenecid, on C-reflex wind-up activity and mechanical nociceptive behavior in a spared nerve injury neuropathic rat model involving sural nerve transection. In addition, the expression of panx1 protein in the dorsal horn of the ipsilateral lumbar spinal cord was measured in sural nerve transected and sham control rats. Sural nerve transection resulted in a lower threshold for C-reflex activation by electric stimulation of the injured hindpaw, together with persistent mechanical hypersensitivity to pressure stimuli applied to the paw. Intrathecal administration of the panx1 blockers significantly depressed the spinal C-reflex wind-up activity in both neuropathic and sham control rats, and decreased mechanical hyperalgesia in neuropathic rats without affecting the nociceptive threshold in sham animals. Western blotting showed that panx1 was similarly expressed in the dorsal horn of lumbar spinal cord from neuropathic and sham rats. The present results constitute the first evidence that panx1 channels play a significant role in the mechanisms underlying central sensitization in neuropathic pain.
    Full-text · Article · Aug 2014 · Pain
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