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Chen H, Cross AC, Thakkar A, Xu H, Li A, Paull D, Noggle SA, Kruger L, Denton TT, Gibson GE. Selective linkage of mitochondrial enzymes to intracellular calcium stores differs between human-induced pluripotent stem cells, neural stem cells, and neurons. J Neurochem 2020; 156:867-879. [PMID: 32865230 DOI: 10.1111/jnc.15160] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 08/12/2020] [Accepted: 08/13/2020] [Indexed: 12/15/2022]
Abstract
Mitochondria and releasable endoplasmic reticulum (ER) calcium modulate neuronal calcium signaling, and both change in Alzheimer's disease (AD). The releasable calcium stores in the ER are exaggerated in fibroblasts from AD patients and in multiple models of AD. The activity of the alpha-ketoglutarate dehydrogenase complex (KGDHC), a key mitochondrial enzyme complex, is diminished in brains from AD patients, and can be plausibly linked to plaques and tangles. Our previous studies in cell lines and mouse neurons demonstrate that reductions in KGDHC increase the ER releasable calcium stores. The goal of these studies was to test whether the relationship was true in human iPSC-derived neurons. Inhibition of KGDHC for one or 24 hr increased the ER releasable calcium store in human neurons by 69% and 144%, respectively. The effect was mitochondrial enzyme specific because inhibiting the pyruvate dehydrogenase complex, another key mitochondrial enzyme complex, diminished the ER releasable calcium stores. The link of KGDHC to ER releasable calcium stores was cell type specific as the interaction was not present in iPSC or neural stem cells. Thus, these studies in human neurons verify a link between KGDHC and releasable ER calcium stores, and support the use of human neurons to examine mechanisms and potential therapies for AD.
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Affiliation(s)
- Huanlian Chen
- Burke Neurological Institute, Brain and Mind Research Institute, Weill Cornell Medicine, White Plains, NY, USA
| | - Abigail C Cross
- Burke Neurological Institute, Brain and Mind Research Institute, Weill Cornell Medicine, White Plains, NY, USA
| | - Ankita Thakkar
- Burke Neurological Institute, Brain and Mind Research Institute, Weill Cornell Medicine, White Plains, NY, USA
| | - Hui Xu
- Burke Neurological Institute, Brain and Mind Research Institute, Weill Cornell Medicine, White Plains, NY, USA
| | - Aiqun Li
- The New York Stem Cell Foundation Research Institute, New York, NY, USA.,Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Dan Paull
- The New York Stem Cell Foundation Research Institute, New York, NY, USA
| | - Scott A Noggle
- The New York Stem Cell Foundation Research Institute, New York, NY, USA
| | - Laken Kruger
- Department of Pharmaceutical Sciences, Washington State University, College of Pharmacy and Pharmaceutical Sciences, Spokane, WA, USA
| | - Travis T Denton
- Department of Pharmaceutical Sciences, Washington State University, College of Pharmacy and Pharmaceutical Sciences, Spokane, WA, USA
| | - Gary E Gibson
- Burke Neurological Institute, Brain and Mind Research Institute, Weill Cornell Medicine, White Plains, NY, USA
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Gibson GE, Chen HL, Xu H, Qiu L, Xu Z, Denton TT, Shi Q. Deficits in the mitochondrial enzyme α-ketoglutarate dehydrogenase lead to Alzheimer's disease-like calcium dysregulation. Neurobiol Aging 2012; 33:1121.e13-24. [PMID: 22169199 PMCID: PMC3321099 DOI: 10.1016/j.neurobiolaging.2011.11.003] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Revised: 10/27/2011] [Accepted: 11/03/2011] [Indexed: 01/08/2023]
Abstract
Understanding the molecular sequence of events that culminate in multiple abnormalities in brains from patients that died with Alzheimer's disease (AD) will help to reveal the mechanisms of the disease and identify upstream events as therapeutic targets. The activity of the mitochondrial α-ketoglutarate dehydrogenase complex (KGDHC) in homogenates from autopsy brain declines with AD. Experimental reductions in KGDHC in mouse models of AD promote plaque and tangle formation, the hallmark pathologies of AD. We hypothesize that deficits in KGDHC also lead to the abnormalities in endoplasmic reticulum (ER) calcium stores and cytosolic calcium following K(+) depolarization that occurs in cells from AD patients and transgenic models of AD. The activity of the mitochondrial enzyme KGDHC was diminished acutely (minutes), long-term (days), or chronically (weeks). Acute inhibition of KGDHC produced effects on calcium opposite to those in AD, while the chronic or long-term inhibition of KGDHC mimicked the AD-related changes in calcium. Divergent changes in proteins released from the mitochondria that affect endoplasmic reticulum calcium channels may underlie the selective cellular consequences of acute versus longer term inhibition of KGDHC. The results suggest that the mitochondrial abnormalities in AD can be upstream of those in calcium.
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Affiliation(s)
- Gary E Gibson
- Department of Neurology and Neuroscience, Weill Cornell Medical College, Burke Medical Research Institute, White Plains, NY 10605, USA.
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Fitzpatrick B, Schuler C, Leggett RE, Levin RM. Calcium effects on superoxide dismutase and catalase of the rabbit urinary bladder muscle and mucosa. Urol Int 2011; 88:107-11. [PMID: 22094966 DOI: 10.1159/000333144] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Accepted: 09/13/2011] [Indexed: 11/19/2022]
Abstract
PURPOSE Superoxide dismutase (SOD) and catalase are two important antioxidant mechanisms that work together to reduce free radical damage. Intracellular free calcium in smooth muscle can change rapidly and many enzymes can be affected. The sensitivity of SOD and catalase activity to calcium was determined in both rabbit bladder smooth muscle and mucosa. MATERIALS AND METHODS Calcium sensitivity was analyzed by determining SOD and catalase activity in muscle and mucosa at the following calcium concentrations: 0 (in the presence of 1 mM EGTA), 1 and 5 mM CaCl(2). RESULTS SOD: EGTA resulted in increased SOD activity of bladder smooth muscle, whereas both 1 and 5 mM calcium significantly decreased SOD activity. EGTA had no effect on SOD activity of the mucosa whereas 1 and 5 mM calcium decreased SOD activity of the muscle. Catalase: 1 mM calcium resulted in decreased catalase activity of the muscle and no change in the activity of the mucosa, whereas 5 mM calcium resulted in increased catalase activity of the mucosa but no change in the activity of the muscle. DISCUSSION Mucosa showed more SOD and catalase activity than the muscle. Both SOD and catalase showed differing sensitivities to EGTA and calcium.
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Grøndahl T, Langmoen IA. Confocal laser scanning microscopy used to monitor intracellular Ca2+ changes in hippocampal CA 1 neurons during energy deprivation. Brain Res 1998; 785:58-65. [PMID: 9526045 DOI: 10.1016/s0006-8993(97)01367-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
An increase in intracellular calcium during cerebral ischemia has been proposed as a common final pathway underlying the events leading to neuronal death. Intracellular calcium has been measured with ion selective electrodes during energy deprivation (ED) in hippocampal slices and with fluorescent techniques in neuronal cultures. In the present study, we describe a novel method to visualize and quantify changes in intracellular calcium in brain slices using Confocal Laser Scanning Microscopy (CLSM). CA 1 pyramidal neurons in hippocampal slices were filled by intracellular injection with a 1:2 mixture of the fluorescent dyes Fluo 3 and Fura Red. The neurons were then visualized using CLSM, and the ratio of the fluorescence from each probe used to quantify intracellular calcium concentrations before and during ED. The free intracellular calcium concentration was 60 nM prior to ED and increased to 24 microM during ED. These results demonstrates that CLSM and fluorescent probes can be used in functional neuronal networks in addition to cell cultures as previously described.
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Affiliation(s)
- T Grøndahl
- Institute for Surgical Research, Department of Opthalmology, Rikshospitalet, National Hospital, University of Oslo, 0027 Oslo, Norway.
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Blass JP, Sheu KF, Piacentini S, Sorbi S. Inherent abnormalities in oxidative metabolism in Alzheimer's disease: interaction with vascular abnormalities. Ann N Y Acad Sci 1997; 826:382-5. [PMID: 9329708 DOI: 10.1111/j.1749-6632.1997.tb48488.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Extensive studies over the last 20 years have documented the existence of inherent abnormalities in oxidative/energy metabolism in Alzheimer's disease (AD). These abnormalities can be linked to characteristics of AD by plausible pathophysiological mechanisms for which there is abundant, robust evidence. The inherent abnormalities in cerebral metabolism of oxygen and glucose can reasonably be expected to interact synergistically with vascular compromise of cerebral oxygen and glucose metabolism in causing brain damage in AD.
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Affiliation(s)
- J P Blass
- Burke Medical Research Institute, Cornell University, White Plains, New York, USA.
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Gleitz J, Tosch C, Peters T. Continuous enzyme-linked fluorometric detection of l-(+)-lactate released from rat brain vesicles under anoxic conditions. J Neurosci Methods 1996. [DOI: 10.1016/0165-0270(96)00006-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Chen TS, Koutsilieri E, Rausch WD. MPP+ selectively affects calcium homeostasis in mesencephalic cell cultures from embryonal C57/Bl6 mice. J Neural Transm (Vienna) 1995; 100:153-63. [PMID: 8962685 DOI: 10.1007/bf01271538] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
1-Methyl-4-phenylpyridinium (MPP+), the active metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) serves as a valuable tool in animal models of Parkinson's disease. Primary cell cultures of mesencephalon from C57/Bl6 mice were used to investigate the effects of various dopaminergic neurotoxins on the intracellular calcium metabolism. MPP+ was compared to its precursor MPTP and a structural analogue paraquat (methylviologen). Direct addition of these neurotoxins (10 microM) to fura-2-labeled cells did not change intracellular calcium concentrations in the presence of 1 mM extracellular calcium. When mesencephalic neurons were exposed to the compounds for 24 hours, only MPP+ led to an increase in calcium concentration in the absence and presence of extracellular calcium (36%, p < 0.05 and 47%, p < 0.01 versus control group). Intracellular calcium concentrations in cortical cultures devoid of dopaminergic cells were not changed by the above neurotoxins. Thus MPP+ is shown to selectively increase intracellular calcium concentrations in mesencephalic cultures.
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Affiliation(s)
- T S Chen
- Institute of Medical Chemistry, University of Veterinary Medicine, Vienna, Austria
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Abstract
The importance of glial cells in controlling the neuronal microenvironment has been increasingly recognized. We now demonstrate that glial cells play an integral role in hippocampal synaptic transmission by using the glial-specific metabolic blocker fluoroacetate (FAC) to selectively inhibit glial cell function. FAC inhibits evoked intracellular postsynaptic potentials (PSPs; IC50 = 39 microM) as well as population PSPs (IC50 = 65 microM) in field CA1 of the guinea pig hippocampal slice. Spontaneous synaptic transmission is concurrently decreased. These effects are time and dose dependent. ATP concentrations in glial but not neuronal elements are also significantly reduced with FAC treatment. Simultaneous application of the metabolic substrate isocitrate with FAC prevents both the reduction in glial ATP concentrations and the decrease in evoked PSPs. Given that isocitrate is selectively taken up by glia, these data further support a glial specific metabolic action of FAC. Additionally, FAC has no postsynaptic effects as peak responses to iontophoretically applied glutamate are unchanged. However, the decay of both iontophoretic and evoked PSPs are prolonged following FAC treatment suggesting inhibition of glutamate uptake may contribute to the FAC-induced depression of synaptic potentials. These results show, for the first time, that glial cells are critical for maintenance of synaptic transmission and suggest a role for glial cells in the modulation of synaptic efficacy.
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Affiliation(s)
- D O Keyser
- Physiology Department, Armed Forces Radiobiology Research Institute, Bethesda, Maryland 20889-5603
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Kelleher JA, Gregory GA, Chan PH. Effect of fructose-1,6-bisphosphate on glutamate uptake and glutamine synthetase activity in hypoxic astrocyte cultures. Neurochem Res 1994; 19:209-15. [PMID: 7910381 DOI: 10.1007/bf00966818] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Astrocytes are important in regulating the microenvironment of neurons both by catabolic and synthetic pathways. The glutamine synthetase (GS) activity observed in astrocytes affects neurons by removing toxic substances, NH3 and glutamate; and by providing an important neuronal substrate, glutamine. This glutamate cycle might play a critical role during periods of hypoxia and ischemia, when an increase in extracellular excitatory amino acids is observed. It was previously shown in our laboratory that fructose-1,6-bisphosphate (FBP) protected cortical astrocyte cultures from hypoxic insult and reduced ATP loss following a prolonged (18-30 hrs) hypoxia. In the present study we established the effects of FBP on the level of glutamate uptake and GS activity under normoxic and hypoxic conditions. Under normoxic conditions, [U-14C]glutamate uptake and glutamine production were independent of FBP treatment; whereas under hypoxic conditions, the initial increase in glutamate uptake and an overall increase in glutamine production in astrocytes were FBP-dependent. Glutamine synthetase activity was dependent on FBP added during the 22 hours of either normoxic- or hypoxic-treatment, hence significant increases in activity were observed due to FBP regardless of the oxygen/ATP levels in situ. These studies suggest that activation of GS by FBP may provide astrocytic protection against hypoxic injury.
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Affiliation(s)
- J A Kelleher
- Department of Neurology, School of Medicine, University of California, San Francisco 94143-0114
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Huang HM, Toral-Barza L, Sheu KF, Gibson GE. The role of cytosolic free calcium in the regulation of pyruvate dehydrogenase in synaptosomes. Neurochem Res 1994; 19:89-95. [PMID: 8139769 DOI: 10.1007/bf00966734] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Calcium homeostasis and mitochondrial oxidative metabolism interact closely in brain and both processes are impaired during hypoxia. Since the regulation of the pyruvate dehydrogenase complex (PDHC) may link these two processes, the relation of cytosolic free calcium ([Ca2+]i) to the activation state of PDHC (PDHa) was assessed in isolated nerve terminals (i.e. synaptosomes) under conditions that alter [Ca2+]i. K+ depolarization elevated [Ca2+]i and PDHa and both responses required external calcium. Treatment with KCN, an in vitro model of hypoxia decreased ATP and elevated [Ca2+]i and PDHa. Furthermore, in the presence of KCN, PDHa became more sensitive to K+ depolarization as indicated by larger changes in PDHa than in [Ca2+]i. The calcium ionophore Br-A23187 elevated [Ca2+]i, but did not affect PDHa. K+ depolarization elevated [Ca2+]i and PDHa even if [Ca2+]i was elevated by prior addition of ionophore or KCN. Previous in vivo studies by others show that PDHa is altered during and after ischemia. The current in vitro results suggest that hypoxia, only one component of ischemia, is sufficient to increase PDHa. These data also further support the notion that PDHa is regulated by [Ca2+]i as well as by other factors such as ATP. Our results are consistent with the concept that PDHa in nerve endings may be affected by [Ca2+]i and that these two processes are clearly linked.
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Affiliation(s)
- H M Huang
- Department of Neurology and Neuroscience, Cornell University Medical College, Burke Medical Research Institute, White Plains, New York 10605
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Kelleher JA, Chan PH, Chan TY, Gregory GA. Modification of hypoxia-induced injury in cultured rat astrocytes by high levels of glucose. Stroke 1993; 24:855-63. [PMID: 8506557 DOI: 10.1161/01.str.24.6.855] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
BACKGROUND AND PURPOSE Preexisting hyperglycemia exacerbates central nervous system injury after transient global and focal cerebral ischemia. Increased anaerobic metabolism with resultant lactic acidosis has been shown to cause the hyperglycemic, neuronal injury. The contribution of astrocytes in producing lactic acidosis under hyperglycemic/ischemic conditions is unclear, whereas the protective role of astrocytes in ischemic-induced neuronal injury has been documented. The ability of astrocytes to maintain energy status and ion homeostasis under hyperglycemic conditions could ultimately reduce neuronal injury. Therefore, we determined the effects of increased glucose concentrations on glucose utilization, lactate production, extracellular pH, and adenosine triphosphate concentrations in hypoxia-treated astrocyte cultures. METHODS Primary astrocytes were prepared from neonatal rat cerebral cortices. After 35 days in vitro, cultures were incubated with 0-60 mmol/L glucose and subjected to hypoxic conditions at 95% N2/5% CO2 for 24 hours. In addition, under high-glucose conditions (30 mmol/L), astrocytes were exposed to up to 72 hours of hypoxia. Determination of lactate dehydrogenase efflux, adenosine triphosphate concentrations, and extracellular lactate concentrations defined astrocyte status. Equiosmolar levels of mannitol were added in place of high glucose concentrations to distinguish hyperosmotic effect. RESULTS When physiological concentrations of glucose (7.5 mmol/L) or lower concentrations were used, significant cell damage occurred with 24 hours of hypoxia, as determined by increased efflux of lactate dehydrogenase and loss of cell protein. When higher glucose concentrations (15-60 mmol/L) were used, efflux of lactate dehydrogenase was similar to that observed in normoxic cultures, despite an increased utilization of glucose. Lactate concentrations in the media at low or normal glucose concentrations exceeded normoxic levels, but higher glucose concentrations (15-30 mmol/L) failed to increase lactate levels further. Values of adenosine triphosphate for hypoxic astrocytes treated with high glucose concentrations were significantly higher than those of astrocytes with zero or low glucose levels. In cultures exposed to hypoxia and high glucose levels (30 mmol/L), no cellular injury was observed before 48 hours of hypoxia. Lactate concentrations in the media increased during the first 24 hours of hypoxia and reached steady state. The pH of the media decreased to 6.4 after 24 hours and 5.5 at 48 hours. The latter pH was concomitant with a marked increase in extracellular lactate dehydrogenase activity. Hyperosmotic mannitol failed to protect cultured astrocytes against hypoxia. CONCLUSIONS Hypoxic injury to mature astrocytes was reduced by the presence of 15-60 mmol/L glucose in the medium during 24-30 hours of hypoxia. Injury occurred when the pH of the medium was < 5.5. This protection was not afforded by the hyperosmotic effect of high glucose concentrations, nor was the hypoxic injury at later time periods with 30 mmol/L glucose mediated solely by lactate accumulation.
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Affiliation(s)
- J A Kelleher
- Department of Neurology, School of Medicine, University of California, San Francisco
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Collard KJ, Menon-Johansson AS. Effects of short-term hypoxia on [3H]glutamate release from preloaded hippocampal and cortical synaptosomes. Neurochem Res 1993; 18:165-70. [PMID: 8097288 DOI: 10.1007/bf01474680] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The effect of short-term hypoxia on the release of [3H]glutamate from preloaded hippocampal and cortical synaptosomes was studied in a rapid superfusion system. The technique minimised the loss of released glutamate by reuptake. The results indicated that the effects of short term hypoxia were qualitatively similar to those reported in previous studies using more long-term hypoxia, but were significantly smaller. The non-Ca(2+)-dependent efflux of glutamate from cortical synaptosomes was increased by hypoxia as was the Ca(2+)-dependent release from hippocampal tissue. Possible mechanisms for these findings were discussed. The small amplitude of these changes in comparison to the effects seen in slowly perfused tissue in vitro and in vivo indicated that the contribution made by changes in neuronal efflux to the overall increase in extracellular glutamate seen in hypoxia is relatively minor.
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Affiliation(s)
- K J Collard
- Department of Physiology, University of Wales College of Cardiff
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Wermelskirchen D, Wilffert B, Peters T. Veratridine-induced intoxication: an in vitro model for the characterization of anti-ischemic compounds? J Basic Clin Physiol Pharmacol 1992; 3:293-321. [PMID: 1285006 DOI: 10.1515/jbcpp.1992.3.4.293] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Due to the complexity of ischemia-induced cellular dysfunction many different pharmacological approaches have been tested to improve cellular ischemia resistance. However, despite the importance of [Na+]i for ischemia-induced dysfunction, only very few studies have investigated the contribution of the Na+ channel to ischemia-induced failure of intracellular ion homeostasis. Since an activation of Na+ channels by veratridine also results in a failure of intracellular ion homeostasis, the veratridine- and ischemia-induced alterations of cellular function were compared. Moreover, despite the difference in the electrophysiological changes induced by veratridine and ischemia, the possible involvement of a slowly inactivating, less selective Na+ channel in both veratridine- and ischemia-induced cellular dysfunction is discussed. As a conclusion it is suggested that veratridine intoxication could be a helpful in vitro method for the characterization of putative anti-ischemic compounds.
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Gibson G, Toral-Barza L, Huang HM. Cytosolic free calcium concentrations in synaptosomes during histotoxic hypoxia. Neurochem Res 1991; 16:461-7. [PMID: 1922657 DOI: 10.1007/bf00965567] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Altered cytosolic free calcium concentrations ([Ca2+]i) accompany impaired brain metabolism and may mediate subsequent effects on brain function and cell death. The current experiments examined whether hypoxia-induced elevations in [Ca2+]i are from external or internal sources. In the absence of external calcium, neither KCl depolarization, histotoxic hypoxia (KCN), nor the combination changed [Ca2+]i. However, with external CaCl2 concentrations as small as 13 microM, KCl depolarization increased [Ca2+]i instantaneously while hypoxia gradually raised [Ca2+]i. The combination of KCN and KCl was additive. Increasing external calcium concentrations up to 2.6 mM exaggerated the effects of K+ and KCN on [Ca2+]i, but raising medium calcium to 5.2 mM did not further augment the rise. Diminishing the sodium in the media, which alters the activity and perhaps the direction of the Na/Ca exchanger, reduced the increase in [Ca2+]i due to hypoxia, but enhanced the KCl response. The changes in ATP following K+ depolarization, KCN or their combination in the presence of physiological calcium concentrations did not parallel alterations in [Ca2+]i, which suggests that diminished activity of the calcium dependent ATPase does not underlie the elevation in [Ca2+]i. Valinomycin, an ionophore which reduces the mitochondrial membrane potential, elevated [Ca2+]i and the effects were additive with K+ depolarization in a calcium dependent manner that paralleled the effects of hypoxia. Together these results suggest that hypoxia-induced elevations of synaptosomal [Ca2+]i are due to an inability of the synaptosome to buffer entering calcium.
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Affiliation(s)
- G Gibson
- Department of Neurology and Neuroscience, Cornell University Medical College, Burke Medical Research Institute, White Plains, NY 10605
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