1,720,982 research outputs found
‐independent somatic release from trigeminal neurons
No full textBesides the nerve endings, the soma of trigeminal neurons also respond to membrane depolarizations with the release of neurotransmitters and neuromodulators in the extracellular space within the ganglion, a process potentially important for the cross-communication between neighboring sensory neurons. In this study, we addressed the dependence of somatic release on Ca2+ influx in trigeminal neurons and the involvement of the different types of voltage-gated Ca2+ (Cav) channels in the process. Similar to the closely related dorsal root ganglion neurons, we found two kinetically distinct components of somatic release, a faster component stimulated by voltage but independent of the Ca2+ influx, and a slower component triggered by Ca2+ influx. The Ca2+ -dependent component was inhibited 80% by ω-conotoxin-MVIIC, an inhibitor of both N- and P/Q-type Cav channels, and 55% by the P/Q-type selective inhibitor ω-agatoxin-IVA. The selective L-type Ca2+ channel inhibitor nimodipine was instead without effect. These results suggest a major involvement of N- and P/Q-, but not L-type Cav channels in the somatic release of trigeminal neurons. Thus antinociceptive Cav channel antagonists acting on the N- and P/Q-type channels may exert their function by also modulating the somatic release and cross-communication between sensory neurons
The Volume-Regulated Anion Channel in Glioblastoma
No full textMalignancy of glioblastoma multiforme (GBM), the most common and aggressive form of human brain tumor, strongly depends on its enhanced cell invasion and death evasion which make surgery and accompanying therapies highly ineffective. Several ion channels that regulate membrane potential, cytosolic Ca2+ concentration and cell volume in GBM cells play significant roles in sustaining these processes. Among them, the volume-regulated anion channel (VRAC), which mediates the swelling-activated chloride current (IClswell) and is highly expressed in GBM cells, arguably plays a major role. VRAC is primarily involved in reestablishing the original cell volume that may be lost under several physiopathological conditions, but also in sustaining the shape and cell volume changes needed for cell migration and proliferation. While experimentally VRAC is activated by exposing cells to hypotonic solutions that cause the increase of cell volume, in vivo it is thought to be controlled by several different stimuli and modulators. In this review we focus on our recent work showing that two conditions normally occurring in pathological GBM tissues, namely high serum levels and severe hypoxia, were both able to activate VRAC, and their activation was found to promote cell migration and resistance to cell death, both features enhancing GBM malignancy. Also, the fact that the signal transduction pathway leading to VRAC activation appears to involve GBM specific intracellular components, such as diacylglicerol kinase and phosphatidic acid, reportedly not involved in the activation of VRAC in healthy tissues, is a relevant finding. Based on these observations and the impact of VRAC in the physiopathology of GBM, targeting this channel or its intracellular regulators may represent an effective strategy to contrast this lethal tumor
Hypoxia, Ion Channels and Glioblastoma Malignancy
No full textThe malignancy of glioblastoma (GBM), the most aggressive type of human brain tumor, strongly correlates with the presence of hypoxic areas within the tumor mass. Oxygen levels have been shown to control several critical aspects of tumor aggressiveness, such as migration/invasion and cell death resistance, but the underlying mechanisms are still unclear. GBM cells express abundant K+ and Cl− channels, whose activity supports cell volume and membrane potential changes, critical for cell proliferation, migration and death. Volume-regulated anion channels (VRAC), which mediate the swelling-activated Cl− current, and the large-conductance Ca2+-activated K+ channels (BK) are both functionally upregulated in GBM cells, where they control different aspects underlying GBM malignancy/aggressiveness. The functional expression/activity of both VRAC and BK channels are under the control of the oxygen levels, and these regulations are involved in the hypoxia-induced GBM cell aggressiveness. The present review will provide a comprehensive overview of the literature supporting the role of these two channels in the hypoxia-mediated GBM malignancy, suggesting them as potential therapeutic targets in the treatment of GBM
Structure, Gating and Basic Functions of the Ca2+-activated K Channel of Intermediate Conductance
No full textThe KCa3.1 channel is the intermediate-conductance member of the Ca2+-activated K channel superfamily. Expressed in excitable and non-excitable cells, the KCa3.1 channel is voltage independent, its opening being exclusively gated by the binding of intracellular Ca2+ to calmodulin, a Ca2+-binding protein constitutively associated with the C-terminus of each KCa3.1 channel α subunit. Upon Ca2+ binding, the KCa3.1 channel activates with high affinity and in highly coordinated fashion giving steep Hill functions and relatively low EC50 values (100-350 nM). This high Ca2+ sensitivity is physiologically modulated by closely associated kinases and phosphatases. The KCa3.1 channel is normally activated by global Ca2+ signals as resulting from Ca2+ released from intracellular stores, or by the refilling influx through store operated Ca2+ channels, but cases of strict functional coupling with Ca2+-selective channels are also found. KCa3.1 channels are highly expressed in many types of cells, where they play major roles in cell migration and death. The control of these complex cellular processes is achieved by KCa3.1 channel regulation of the driving force for Ca2+ entry from the extracellular medium, and by mediating the K+ efflux required for cell volume control. This paper aims at illustrating the main structural, biophysical and modulatory properties of the KCa3.1 channel, and at providing an account of experimental data on its role in volume regulation and Ca2+ signals
Ion Channels in Glioma Malignancy
No full textBrain tumors come in many types and differ greatly in outcome. They are classified by the cell of origin (astrocytoma, ependymoma, meningioma, medulloblastoma, glioma), although more recently molecular markers are used in addition to histology. Brain tumors are graded (from I to IV) to measure their malignancy. Glioblastoma, one of the most common adult primary brain tumors, displays the highest malignancy (grade IV), and median survival of about 15 months. Main reasons for poor outcome are incomplete surgical resection, due to the highly invasive potential of glioblastoma cells, and chemoresistance that commonly develops during drug treatment. An important role in brain tumor malignancy is played by ion channels. The Ca2+-activated K+ channels of large and intermediate conductance, KCa3.1 and KCa1.1, and the volume-regulated anion channel, whose combined activity results in the extrusion of KCl and osmotic water, control cell volume, and in turn migration, invasion, and apoptotic cell death. The transient receptor potential (TRP) channels and low threshold-activated Ca (T-type) channels have equally critical role in brain tumor malignancy, as dysregulated Ca2+ signals heavily impact on glioma cell proliferation, migration, invasion. The review provides an overview of the current evidence involving these channels in brain tumor malignancy, and the application of these insights in the light of future prospects for experimental and clinical practice
Identification of Key Signaling Molecules Involved in the Activation of the Swelling-Activated Chloride Current in Human Glioblastoma Cells
No full textThe swelling-activated chloride current (I (Cl,Vol)) is abundantly expressed in glioblastoma (GBM) cells, where it controls cell volume and invasive migration. The transduction pathway mediating I (Cl,Vol) activation in GBM cells is, however, poorly understood. By means of pharmacological and electrophysiological approaches, on GL-15 human GBM cells we found that I (Cl,Vol) activation by hypotonic swelling required the activity of a U73122-sensitive phospholipase C (PLC). I (Cl,Vol) activation could also be induced by the membrane-permeable diacylglycerol (DAG) analog OAG. In contrast, neither calcium (Ca2+) chelation by BAPTA-AM nor changes in PKC activity were able to affect I (Cl,Vol) activation by hypotonic swelling. We further found that R59022, an inhibitor of diacylglycerol kinase (DGK), reverted I (Cl,Vol) activation, suggesting the involvement of phosphatidic acid. In addition, I (Cl,Vol) activation required the activity of a EHT1864-sensitive Rac1 small GTPase and the resulting actin polymerization, as I (Cl,Vol) activation was prevented by cytochalasin B. We finally show that I (Cl,Vol) can be activated by the promigratory fetal calf serum in a PLC- and DGK-dependent manner. This observation is potentially relevant because blood serum can likely come in contact with glioblastoma cells in vivo as a result of the tumor-related partial breakdown of the blood-brain barrier. Given the relevance of I (Cl,Vol) in GBM cell volume regulation and invasiveness, the several key signaling molecules found in this study to be involved in the activation of the I (Cl,Vol) may represent potential therapeutic targets against this lethal cancer
Expression and function of a CP339,818-sensitive K+ current in a subpopulation of putative nociceptive neurons from adult mouse trigeminal ganglia
No full textA method to identify tissue cell subpopulations with distinct multi-molecular profiles from data on co-localization of two markers at a time: the case of sensory ganglia
No full textMost biological tissues are characterized by high morphological and functional cell heterogeneity. To investigate this heterogeneity at the molecular level, scientists have tried to associate specific sets of molecular markers (molecular profiles) to functionally distinct cell subpopulations, evaluating their expression using immunochemistry and in situ hybridization techniques. NEW METHOD: We propose here a novel analysis that allows the estimation of the frequency of cells expressing distinct molecular profiles starting from data on the co-expression of two markers at a time. In order to facilitate the application of the proposed analysis, we developed and make available a user-friendly window-based software. RESULTS: We successfully applied the analytical method to experimental data from adult rat sensory neurons. In a first application we subgrouped DRG neurons in 11 subpopulations on the basis of the co-expression of 6 molecular markers (the TRPs type V1, A1, and M8 and the trks type A, B, and C). In a second application we found that while rat DRG have significant frequencies of peptidergic/IB4-negative and non-peptidergic/IB4-positive nociceptors, rat TG neurons lack almost completely
these two subpopulations. COMPARISON WITH EXISTING METHODS: The analytical method here proposed overcomes the limitations of the presently available experimental techniques, most of which can assess the co-expression of only few molecular markers at a time. CONCLUSIONS: This new method will allow a better understanding of the molecular and cellular heterogeneity of tissues in normal and pathological conditions
Identification of Key Signaling Molecules Involved in the Activation of the Swelling-Activated Chloride Current in Human Glioblastoma Cells
No full textHypoxia Modulates the Swelling-Activated Cl Current in Human Glioblastoma Cells: Role in Volume Regulation and Cell Survival
No full textThe malignancy of glioblastoma multiforme (GBM), the most common human brain tumor, correlates with the presence of hypoxic areas,
but the underlying mechanisms are unclear. GBM cells express abundant Cl channels whose activity supports cell volume and membrane
potential changes, ultimately leading to cell proliferation, migration, and escaping death. In non-tumor tissues Cl channels are modulated by
hypoxia, which prompted us to verify whether hypoxia would also modulate Cl channels in GBM cells. Our results show that in GBM cell
lines, acute application of a hypoxic solution activates a Cl current displaying the biophysical and pharmacological features of the swellingactivated
Cl current (ICl,swell). We also found that acute hypoxia increased the cell volume by about 20%, and a 30% hypertonic solution
partially inhibited the hypoxia-activated Cl current, suggesting that cell swelling and the activation of the Cl current are sequential events.
Notably, the hypoxia-induced cell swelling was followed by a regulatory volume decrease (RVD) mediated mainly by ICl,swell. Since, a
hypoxia-induced prolonged cell swelling is usually regarded as a death insult, we hypothesized that the hypoxia-activated Cl current could
limit cell swelling and prevent necrotic death of GBM cells under hypoxic conditions. In accordance, we found that the ICl,swell inhibitor
DCPIB hampered the RVD process, and more importantly it sensibly increased the hypoxia-induced necrotic death in these cells. Taken
together, these results suggest that Cl channels are strongly involved in the survival of GBM cells in a hypoxic environment, and may thus
represent a new therapeutic target for this malignant tumor
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