5-(N-Ethyl-N-isopropyl)-amiloride inhibits amino acid release from the ischemic rat cerebral cortex: role of Na+–H+ exchange

doi:10.1016/S0006-8993(98)00984-6

Brain Research

Volume 812, Issues 1–2, 23 November 1998, Pages 297-300

https://doi.org/10.1016/S0006-8993(98)00984-6 Get rights and content

Abstract

The effect of the selective Na⁺/H⁺ antiporter inhibitor 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) on amino acid release from the ischemic/reperfused rat cerebral cortex was investigated using a cortical cup technique. EIPA (25 μM in artificial cerebrospinal fluid), applied topically, inhibited the ischemia–reperfusion evoked efflux of aspartate, glutamate, γ-aminobutyric acid, taurine and phosphoethanolamine. Reductions in the ischemia-evoked releases of these amino acids suggest that ischemia precipitates acidosis, Na⁺/H⁺ exchange and cell swelling with amino acid release as the cells mount a regulatory volume decrease response. EIPA, by blocking Na⁺/H⁺ exchange, would reduce cell swelling and the resulting amino acid release.

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Acknowledgements

Supported by USPHS award NS26912-09.

References (27)

L.P Caragine et al.
Real-time measurement of ischemia-evoked glutamate release in the cerebral cortex of four and eleven vessel rat occlusion models
Brain Res.
(1998)
D.E Jakubovicz et al.
Cell swelling following recovery from acidification in C₆ glioma cells: an in vitro model of postischemic brain edema
Brain Res.
(1987)
D.E Jakubovicz et al.
Lactic acid-induced swelling in C₆ glial cells via Na⁺/H⁺ exchange
Brain Res.
(1989)
H Liu et al.
Ethylisopropylamiloride diminishes changes in intracellular Na, Ca and pH in ischemic newborn myocardium
J. Mol. Cell. Cardiol.
(1997)
J.W Phillis et al.
Mechanisms of glutamate and aspartate release in the ischemic rat cerebral cortex
Brain Res.
(1996)
J.W Phillis et al.
Inhibition by anion channel blockers of ischemia-evoked release of excitotoxic and other amino acids from rat cerebral cortex
Brain Res.
(1997)
J.W Phillis et al.
Tamoxifen, a chloride channel blocker, reduces glutamate and aspartate release from the ischemic cerebral cortex
Brain Res.
(1998)
D.W Choi
Excitotoxic cell death
J. Neurobiol.
(1992)
S Grinstein et al.
Mechanism of regulation of the Na⁺/H⁺ exchanger
J. Membr. Biol.
(1986)
K.-I. Katsura, Acidosis as a complicating factor in cerebral ischemia, in: K.M.A. Welch, L. Caplan, D. Reis, B. Weir,...

O Kempski et al.

Glial swelling during extracellular acidosis in vitro

Stroke

(1988)

H.K Kimelberg et al.

SITS-inhibitable Cl⁻ transport and Na⁺-dependent H⁺ production in primary astroglial cultures

Brain Res.

(1979)

H.K Kimelberg et al.

Swelling-induced release of glutamate, aspartate, and taurine from astrocyte cultures

J. Neurosci.

(1990)

Cited by (17)

Solute carrier transporters: the metabolic gatekeepers of immune cells
2020, Acta Pharmaceutica Sinica B
Citation Excerpt :
Studies on these transporters will promote a better understanding of the functions of different metal ions in the immune system. The information reviewed above metal ion transporters involved in immune cells are summarized in Table 297–99,154-174. As an indispensable component of over 300 different enzymes, zinc (Zn2+) participates in scores of essential biochemical processes in addition to its structural roles175,176.
Solute carrier (SLC) transporters meditate many essential physiological functions, including nutrient uptake, ion influx/efflux, and waste disposal. In its protective role against tumors and infections, the mammalian immune system coordinates complex signals to support the proliferation, differentiation, and effector function of individual cell subsets. Recent research in this area has yielded surprising findings on the roles of solute carrier transporters, which were discovered to regulate lymphocyte signaling and control their differentiation, function, and fate by modulating diverse metabolic pathways and balanced levels of different metabolites. In this review, we present current information mainly on glucose transporters, amino-acid transporters, and metal ion transporters, which are critically important for mediating immune cell homeostasis in many different pathological conditions.
Disruption of ionic and cell volume homeostasis in cerebral ischemia: The perfect storm
2007, Pathophysiology
The mechanisms of brain tissue damage in stroke are strongly linked to the phenomenon of excitotoxicity, which is defined as damage or death of neural cells due to excessive activation of receptors for the excitatory neurotransmitters glutamate and aspartate. Under physiological conditions, ionotropic glutamate receptors mediate the processes of excitatory neurotransmission and synaptic plasticity. In ischemia, sustained pathological release of glutamate from neurons and glial cells causes prolonged activation of these receptors, resulting in massive depolarization and cytoplasmic Ca²⁺ overload. High cytoplasmic levels of Ca²⁺ activate many degradative processes that, depending on the metabolic status, cause immediate or delayed death of neural cells. This traditional view has been expanded by a number of observations that implicate Cl⁻ channels and several types of non-channel transporter proteins, such as the Na⁺,K⁺,2Cl⁻ cotransporter, Na⁺/H⁺ exchanger, and Na⁺/Ca²⁺ exchanger, in the development of glutamate toxicity. Some of these ion transporters increase tissue damage by promoting pathological cell swelling and necrotic cell death, while others contribute to a long-term accumulation of cytoplasmic Ca²⁺. This brief review is aimed at illustrating how the dysregulation of various ion transport processes combine in a ‘perfect storm’ that disrupts neural ionic homeostasis and culminates in the irreversible damage and death of neural cells. The clinical relevance of individual transporters as targets for therapeutic intervention in stroke is also briefly discussed.
Astroglia: Important mediators of traumatic brain injury
2007, Progress in Brain Research
Citation Excerpt :
Activation of these pH-stabilizing mechanisms during TBI-induced acidosis would elicit increases in glial intracellular Na+ and Cl− along with osmotically obligated water leading to astrocyte swelling (Kempski et al., 1988; Jakubovicz and Klip, 1989). Recent studies have demonstrated that amiloride analogues that inhibit the NHE-1 significantly reduce hippocampal extracellular glutamate levels following transient cerebral ischemia in rat (Phillis et al., 1998) and reduce CA1 hippocampal neuronal cell death assessed at 6 days after transient cerebral ischemia in the gerbil (Phillis et al., 1999). Phillis et al. (1999) attributed their results to the actions of amiloride in reducing astrocyte swelling and thereby increasing extracellular space.
Traumatic brain injury (TBI) research to date has focused almost exclusively on the pathophysiology of injured neurons with very little attention paid to non-neuronal cells. However in the past decade, exciting discoveries have challenged this century-old view of passive glial cells and have led to a reinterpretation of the role of glial cells in central nervous system (CNS) biology and pathology. In this chapter we review several lines of evidence, indicating that glial cells, particularly astrocytes, are active partners to neurons in the brain, and summarize recent findings that detail the significance of astrocyte pathology in traumatic brain injury.
Energy utilization in the ischemic/reperfused brain
2002, International Review of Neurobiology
Stroke and cardiac arrest are among the leading contributors to mortality and morbidity. Elevated blood glucose levels, as in diabetes, are associated with an increase in ischemic brain injuries and a reduction in the likelihood of functional recovery. Pre-, but not post-, ischemic hyperglycemia exaggerates brain damage in the animal models of cerebral ischemic injury. This outcome has been widely attributed to a rise in lactate production from anaerobic glycolysis, with a concomitant tissue acidosis. It has been assumed that acidosis is toxic to neurons, initiating the dying process. It was therefore disturbing to observe that hyperglycemia reduced the ischemia-evoked release of the excitotoxic amino acids, glutamate and aspartate, which is considered to be among the primary causes of cerebral ischemic injury. This result suggested that hyperglycemia might actually have a cerebroprotective action during the ischemic episode, possibly due to lactate formation in astrocytes, with lactate serving as a source of metabolic energy for neurons, and that the damaging effects of hyperglycemia occur during reperfusion, as the intracellular pH reverts to normal levels. The evidence in support of this suggestion came from the observation that there was a marked increase in brain extracellular free fatty acid levels during the initial minutes of reperfusion, indicative of a sudden increase in phospholipase activation and cell membrane degradation. Future directions for research will involve a detailed examination of mitochondrial function in ischemia/reperfusion brains. This chapter reviews the recent findings on cerebral metabolism in normoxic and ischemic brains exposed to the physiologic and elevated levels of glucose. The role of insulin, plasma levels of which are depleted in many diabetics, in brain metabolism is also discussed.
Inhibition of Na+/H+ exchanger reduces infarct volume of focal cerebral ischemia in rats
2001, Brain Research
Citation Excerpt :
Inhibition of NHE produced protective effect on ischemic cultured neuron, and inhibited glial cell swelling during acidosis [10,11,34]. It has been reported that ischemic acidosis-evoked excitatory amino acid release from rat cerebral cortex was reduced by an inhibitor of NHE in vivo [25]. Kuribayashi et al. [19] using a transient middle cerebral artery (MCA) occlusion model have recently shown the protective effect of an NHE inhibitor on focal cerebral ischemia in rats [19].
Activation of Na⁺/H⁺ exchanger (NHE) may have an important role in ischemic cell death by means of intracellular overload of Na⁺ and Ca²⁺. Recent evidence has suggested that inhibitors of NHE have protective effects on myocardial ischemia both in vivo and in vitro. In this study, we tested the hypothesis that FR183998, an inhibitor of NHE, reduces infarct volume produced by focal cerebral ischemia in rats. We used 20 male spontaneously hypertensive rats. Either FR183998 (1 mg/kg; n=10), or vehicle (n=10) was given intravenously to the rats and the distal middle cerebral artery of each animal was occluded using a photothrombotic technique. We measured regional cerebral blood flow using laser-Doppler flowmetry throughout the experiments. After 3 days, infarct volume was measured in each animal group. To estimate the brain edema, we also calculated the cortical volume in both hemispheres. The infarct volume in the FR183998-treated group (82±8 mm³, mean±S.E.M.) was significantly smaller than that in the control group (115±12 mm³) (P=0.034). The cortical volume of the occluded side in the FR183998-treated group (359±7 mm³) tended to be smaller than that in the control group (378±9 mm³) (P=0.116). The regional cerebral blood flow and physiological variables during ischemia were not significantly different between the two groups throughout the experiments. These results suggest that inhibition of NHE by FR183998 may have beneficial effects in reducing infarct volume and brain edema during cerebral ischemia. Thus, NHE may play an important role in the development of neuronal damage during acute cerebral ischemia.
Inhibition of Na+/Ca2+ exchange by KB-R7943, a novel selective antagonist, attenuates phosphoethanolamine and free fatty acid efflux in rat cerebral cortex during ischemia-reperfusion injury
2001, Brain Research
Citation Excerpt :
HPLC assays of superperfusate free fatty acid contents were initiated within hours using previously published procedures [38]. Similarly, HPLC assays of superfusates for amino acid concentrations were performed [32]. Statistical differences for free fatty acid and amino acid levels between control and drug-treated animals were determined by a two-tailed Student’s t-test for each collection period.
Reversal of the Na⁺/Ca²⁺ exchanger (NCX) occurs during ischemia–reperfusion injury as a result of changes in intracellular pH and sodium concentration. Inhibition of NCXs has been shown to be neuroprotective in vitro. In this study, we evaluated the effects of KB-R7943 (50 μM), a specific inhibitor of the reverse mode of NCX, applied topically onto rat cerebral cortex prior to and during ischemia. Amino acid and free fatty acid levels in cortical superfusates, withdrawn at 10-min intervals from bilateral cortical windows, were analyzed by high-performance liquid chromatography. During a 20-min period of ischemia in control animals, there were significant increases in all amino acids and in all FFAs. Following reperfusion, all FFAs remained significantly elevated. Application of KB-R7943 (50 μM) significantly inhibited effluxes of phosphoethanolamine, but had no effect on glutamate, aspartate, taurine or GABA levels. KB-R7943 also resulted in significant reductions in levels of myristic, docosahexaenoic and arachidonic acid during ischemia and in reperfusion levels of arachidonic and docosahexaenoic acids. These data indicate that inhibition of Na⁺/Ca²⁺ exchange likely prevented the activation of phospholipases that usually occurs following an ischemic insult as evidenced by its attenuation of phosphoethanolamine and free fatty acid efflux. The inhibition of phospholipases may be an essential component of the neuroprotective benefits of Na⁺/Ca²⁺ exchange inhibitors in ischemia–reperfusion injury and may provide a basis for their possible use in therapeutic strategies for stroke.

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Brain Research

Abstract

Section snippets

Acknowledgements

References (27)

Real-time measurement of ischemia-evoked glutamate release in the cerebral cortex of four and eleven vessel rat occlusion models

Brain Res.

Cell swelling following recovery from acidification in C₆ glioma cells: an in vitro model of postischemic brain edema

Brain Res.

Lactic acid-induced swelling in C₆ glial cells via Na⁺/H⁺ exchange

Brain Res.

Ethylisopropylamiloride diminishes changes in intracellular Na, Ca and pH in ischemic newborn myocardium

J. Mol. Cell. Cardiol.

Mechanisms of glutamate and aspartate release in the ischemic rat cerebral cortex

Brain Res.

Inhibition by anion channel blockers of ischemia-evoked release of excitotoxic and other amino acids from rat cerebral cortex

Brain Res.

Tamoxifen, a chloride channel blocker, reduces glutamate and aspartate release from the ischemic cerebral cortex

Brain Res.

Excitotoxic cell death

J. Neurobiol.

Mechanism of regulation of the Na⁺/H⁺ exchanger

J. Membr. Biol.

Glial swelling during extracellular acidosis in vitro

Stroke

SITS-inhibitable Cl⁻ transport and Na⁺-dependent H⁺ production in primary astroglial cultures

Brain Res.

Swelling-induced release of glutamate, aspartate, and taurine from astrocyte cultures

J. Neurosci.

Cited by (17)

Solute carrier transporters: the metabolic gatekeepers of immune cells

Disruption of ionic and cell volume homeostasis in cerebral ischemia: The perfect storm

Astroglia: Important mediators of traumatic brain injury

Energy utilization in the ischemic/reperfused brain

Inhibition of Na<sup>+</sup>/H<sup>+</sup> exchanger reduces infarct volume of focal cerebral ischemia in rats

Inhibition of Na<sup>+</sup>/Ca<sup>2+</sup> exchange by KB-R7943, a novel selective antagonist, attenuates phosphoethanolamine and free fatty acid efflux in rat cerebral cortex during ischemia-reperfusion injury

Short communication5-(N-Ethyl-N-isopropyl)-amiloride inhibits amino acid release from the ischemic rat cerebral cortex: role of Na+–H+ exchange

Abstract

Section snippets

Acknowledgements

Brain Res.

Brain Res.

Brain Res.

J. Mol. Cell. Cardiol.

Brain Res.

Brain Res.

Brain Res.

Excitotoxic cell death

J. Neurobiol.

Mechanism of regulation of the Na+/H+ exchanger

J. Membr. Biol.

Glial swelling during extracellular acidosis in vitro

Stroke

SITS-inhibitable Cl− transport and Na+-dependent H+ production in primary astroglial cultures

Brain Res.

Swelling-induced release of glutamate, aspartate, and taurine from astrocyte cultures

J. Neurosci.

Short communication
5-(N-Ethyl-N-isopropyl)-amiloride inhibits amino acid release from the ischemic rat cerebral cortex: role of Na⁺–H⁺ exchange

Mechanism of regulation of the Na⁺/H⁺ exchanger

SITS-inhibitable Cl⁻ transport and Na⁺-dependent H⁺ production in primary astroglial cultures