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Biomedical subjects

M Lazdunski

Publications and source records attributed to M Lazdunski.

At least 73 records · Page 4Linked to original sources
PubMed1999

Riluzole prevents ischemic spinal cord injury caused by aortic crossclamping.

BACKGROUND: Recent studies support the involvement of glutamate neurotoxicity in the pathophysiology of spinal cord injury induced by aortic crossclamping. We investigated the effects of riluzole, a neuroprotective drug that blocks glutamatergic neurotransmission, in a rabbit model of spinal cord ischemia. METHODS: The infrarenal aortas of New Zealand White albino rabbits (n = 40) were occluded for 40 minutes. Experimental groups were as follows: sham operation group (n = 5), control group undergoing occlusion but receiving no pharmacologic intervention (n = 10), experimental group A (n = 10) receiving 8 mg/kg riluzole intravenously 30 minutes before ischemia, experimental group B (n = 10) receiving 4 mg/kg riluzole intravenously 30 minutes before ischemia and at the onset of reperfusion, and experimental group C (n = 10) receiving 8 mg/kg riluzole intravenously at the onset of reperfusion. Neurologic status was assessed at 6, 24, and 48 hours after the operation and then daily until the fifth day. All animals were killed at 24, 48, or 120 hours after the operation. Spinal cords were harvested for histopathologic studies, immunohistochemical studies for microtubule-associated protein 2, and search for morphologic features of apoptosis by the terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate-biotin nick-end labeling staining method. RESULTS: All animals in the control group became paraplegic. Except for 1 rabbit in group C, all riluzole-treated animals had better neurologic function. Luxol fast blue and terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate-biotin nick-end labeling staining methods demonstrated typical morphologic changes characteristic of necrosis and apoptosis in control animals. Riluzole prevented or attenuated ischemia-induced necrosis, apoptosis, and cytoskeletal proteolysis, depending on the dose and the timing of administration. CONCLUSION: Riluzole may have therapeutic utility during high-risk operations on the thoracoabdominal aorta.

Animals↗
PubMed1999

Receptors for a growing family of secreted phospholipases A2.

Phospholipases A2 (PLA2s) are enzymes that catalyse the hydrolysis of the sn-2 acyl bond of glycerophospholipids to produce free fatty acids and lysophospholipids. Numerous intracellular and secreted PLA2s (sPLA2s) have now been characterized. Because PLA2 products are important for cell signalling and the biosynthesis of biologically active lipids, including eicosanoids and platelet-activating factor, PLA2s are generally considered as key enzymes that control the release of lipid mediator precursors. However, the increasing number of mammalian sPLA2s and the recent identification of different membrane proteins that bind sPLA2s makes it likely that these enzymes also behave as ligands for receptors, and that their physiological function is not limited to their catalytic activity. Here, the current state of awareness regarding the different types of sPLA2-binding proteins is described. To date, five distinct mammalian sPLA2s and two main types (M and N) of sPLA2 receptors have been identified. Because most is known about the M-type receptor, particular attention will be paid to it, including a description of it molecular properties and of its possible biological roles with regard to sPLA2 function.

Animals↗
PubMed1999

Inhalational anesthetics activate two-pore-domain background K+ channels.

Volatile anesthetics produce safe, reversible unconsciousness, amnesia and analgesia via hyperpolarization of mammalian neurons. In molluscan pacemaker neurons, they activate an inhibitory synaptic K+ current (IKAn), proposed to be important in general anesthesia. Here we show that TASK and TREK-1, two recently cloned mammalian two-P-domain K+ channels similar to IKAn in biophysical properties, are activated by volatile general anesthetics. Chloroform, diethyl ether, halothane and isoflurane activated TREK-1, whereas only halothane and isoflurane activated TASK. Carboxy (C)-terminal regions were critical for anesthetic activation in both channels. Thus both TREK-1 and TASK are possibly important target sites for these agents.

Amino Acid Sequence↗
PubMed1999

Effects of phrixotoxins on the Kv4 family of potassium channels and implications for the role of Ito1 in cardiac electrogenesis.

1. In the present study, two new peptides, phrixotoxins PaTx1 and PaTx2 (29-31 amino acids), which potently block A-type potassium currents, have been purified from the venom of the tarantula Phrixotrichus auratus. 2. Phrixotoxins specifically block Kv4.3 and Kv4.2 currents that underlie I(to1), with an 5 < IC50 < 70 nM, by altering the gating properties of these channels. 3. Neither are the Shaker (Kv1), Shab (Kv2) and Shaw (Kv3) subfamilies of currents, nor HERG, KvLQT1/IsK, inhibited by phrixotoxins which appear specific of the Shal (Kv4) subfamily of currents and also block I(to1) in isolated murine cardiomyocytes. 4. In order to evaluate the physiological consequences of the Ito1 inhibition, mice were injected intravenously with PaTx1, which resulted in numerous transient cardiac adverse reactions including the occurrence of premature ventricular beats, ventricular tachycardia and different degrees of atrioventricular block. 5. The analysis of the mouse electrocardiogram showed a dose-dependent prolongation of the QT interval, chosen as a surrogate marker for their ventricular repolarization, from 249 +/- 11 to 265 +/- 8 ms (P < 0.05). 6. It was concluded that phrixotoxins, are new and specific blockers of Kv4.3 and Kv4.2 potassium currents, and hence of I(to1) that will enable further studies of Kv4.2 and Kv4.3 channel and/or I(to1) expression.

Amino Acid Sequence↗
PubMed1999

Mutually protective actions of kainic acid epileptic preconditioning and sublethal global ischemia on hippocampal neuronal death: involvement of adenosine A1 receptors and K(ATP) channels.

Preconditioning with sublethal ischemia attenuates the detrimental effects of subsequent prolonged ischemic insults. This research elucidates potential in vivo cross-tolerance between different neuronal death-generating treatments such as kainate administration, which induces seizures and global ischemia. This study also investigates the effects of a mild epileptic insult on neuronal death in rat hippocampus after a subsequent, lethal epileptic stress using kainic acid (KA) as a model of epilepsy. Three preconditioning groups were as follows: group 1 was injected with 5 mg/kg KA before a 6-minute global ischemia; group 2 received a 3-minute global ischemia before 7.5 mg/kg KA; and group 3 was injected with a 5-mg/kg dose of KA before a 7.5-mg/kg KA injection. The interval between treatments was 3 days. Neuronal degeneration, revealed by the silver impregnation method and analysis of cresyl violet staining, was markedly reduced in rats preconditioned with a sublethal ischemia or a 5-mg/kg KA treatment. Labeling with terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'triphosphate-biotin nick-end labeling and DNA laddering confirmed the component of DNA fragmentation in the death of ischemic and epileptic neurons and its reduction in all preconditioned animals. The current study supports the existence of bidirectional cross-tolerance between KA excitotoxicity and global ischemia and suggests the involvement of adenosine A1 receptors and sulfonylurea- and ATP-sensitive K+ channels in this protective phenomenon.

Animals↗
PubMed1999

Secreted phospholipases A(2), a new class of HIV inhibitors that block virus entry into host cells.

Mammalian and venom secreted phospholipases A(2) (sPLA(2)s) have been associated with a variety of biological effects. Here we show that several sPLA(2)s protect human primary blood leukocytes from the replication of various macrophage and T cell-tropic HIV-1 strains. Inhibition by sPLA(2)s results neither from a virucidal effect nor from a cytotoxic effect on host cells, but it involves a more specific mechanism. sPLA(2)s have no effect on virus binding to cells nor on syncytia formation, but they prevent the intracellular release of the viral capsid protein, suggesting that sPLA(2)s block viral entry into cells before virion uncoating and independently of the coreceptor usage. Various inhibitors and catalytic products of sPLA(2) have no effect on HIV-1 infection, suggesting that sPLA(2) catalytic activity is not involved in the antiviral effect. Instead, the antiviral activity appears to involve a specific interaction of sPLA(2)s to host cells. Indeed, of 11 sPLA(2)s from venom and mammalian tissues assayed, 4 venom sPLA(2)s were found to be very potent HIV-1 inhibitors (ID(50) < 1 nM) and also to bind specifically to host cells with high affinities (K(0.5) < 1 nM). Although mammalian pancreatic group IB and inflammatory-type group IIA sPLA(2)s were inactive against HIV-1 replication, our results could be of physiological interest, as novel sPLA(2)s are being characterized in humans.

Animals↗
PubMed1999

Riluzole improves functional recovery after ischemia in the rat retina.

PURPOSE: Retinal ischemia leads to neuronal death. The effects of riluzole, a drug that protects against the deleterious effect of cerebral ischemia by acting on several types of ion channels and blocking glutamatergic neurotransmission, were investigated in a rat model of retinal ischemic injury. METHODS: Retinal ischemia was induced by increasing intraocular pressure above systolic blood pressure for 30 minutes. Electroretinograms were recorded before ischemia and at different periods of reperfusion. Riluzole was injected or topically applied to the eye before or after ischemia and twice daily during the reperfusion period. Retinas were harvested for histopathology (toluidine blue and silver-impregnation stainings, Tdt-dUTP terminal nick-end labeling [TUNEL] method) and immunohistochemistry for cytoskeletal glial fibrillary acid protein and c-jun NH2-terminal kinase (p-JNK). RESULTS: Ischemia for 30 minutes caused a reduction of a- and b-waves of the electroretinogram. Systemic and topical treatments with riluzole significantly enhanced the recovery of the reduced a- and b-waves after defined reperfusion times. Riluzole also prevented or attenuated ischemia-induced retinal cell death (necrosis and apoptosis) and reduced the activation of p-JNK, c-jun phosphorylation, and the increase of cytoskeletal proteins induced by ischemic injury. CONCLUSIONS: Riluzole acted in vivo as a potent neuroprotective agent against pressure-induced ischemia. Therefore, riluzole may be a major drug for use in protection against retinal injury.

Administration, Topical↗
PubMed1998

Cloning and expression of a novel pH-sensitive two pore domain K+ channel from human kidney.

A complementary DNA encoding a novel K+ channel, called TASK-2, was isolated from human kidney and its gene was mapped to chromosome 6p21. TASK-2 has a low sequence similarity to other two pore domain K+ channels, such as TWIK-1, TREK-1, TASK-1, and TRAAK (18-22% of amino acid identity), but a similar topology consisting of four potential membrane-spanning domains. In transfected cells, TASK-2 produces noninactivating, outwardly rectifying K+ currents with activation potential thresholds that closely follow the K+ equilibrium potential. As for the related TASK-1 and TRAAK channels, the outward rectification is lost at high external K+ concentration. The conductance of TASK-2 was estimated to be 14.5 picosiemens in physiological conditions and 59.9 picosiemens in symmetrical conditions with 155 mM K+. TASK-2 currents are blocked by quinine (IC50 = 22 microM) and quinidine (65% of inhibition at 100 microM) but not by the other classical K+ channel blockers tetraethylammonium, 4-aminopyridine, and Cs+. They are only slightly sensitive to Ba2+, with less than 17% of inhibition at 1 mM. As TASK-1, TASK-2 is highly sensitive to external pH in the physiological range. 10% of the maximum current was recorded at pH 6. 5 and 90% at pH 8.8. Unlike all other cloned channels with two pore-forming domains, TASK-2 is essentially absent in the brain. In human and mouse, TASK-2 is mainly expressed in the kidney, where in situ hybridization shows that it is localized in cortical distal tubules and collecting ducts. This localization, as well as its functional properties, suggest that TASK-2 could play an important role in renal K+ transport.

Amino Acid Sequence↗
PubMed1998

The KCNQ2 potassium channel: splice variants, functional and developmental expression. Brain localization and comparison with KCNQ3.

Benign familial neonatal convulsions, an autosomal dominant epilepsy of newborns, are linked to mutations affecting two six-transmembrane potassium channels, KCNQ2 and KCNQ3. We isolated four splice variants of KCNQ2 in human brain. Two forms generate, after transient expression in COS cells, a potassium-selective current similar to the KCNQ1 current. L-735,821, a benzodiazepine molecule which inhibits the KCNQ1 channel activity (EC50 = 0.08 microM), also blocks KCNQ2 currents (EC50 = 1.5 microM). Using in situ hybridization, KCNQ2 and KCNQ3 have been localized within the central nervous system, in which they are expressed in the same areas, mainly in the hippocampus, the neocortex and the cerebellar cortex. During brain development, KCNQ3 is expressed later than KCNQ2.

Aging↗
PubMed1998

Identification, functional expression and chromosomal localisation of a sustained human proton-gated cation channel.

Non-inactivating or slowly inactivating proton-gated cation channels are thought to play an important role in the perception of pain that accompanies tissue acidosis. We have identified a novel human proton-gated cation channel subunit that has biphasic desensitisation kinetics with both a rapidly inactivating Na+-selective and a sustained component. The protein shares 84% sequence identity with the proton-gated cation channel rASIC3 (rDRASIC) from rat sensory neurones. The biphasic desensitisation kinetics and the sequence homology suggest that this novel clone (hASIC3) is the human orthologue of rASIC3 (rDRASIC). While rASIC3 (rDRASIC) requires very acidic pH (pH < 4.5) for activation of the sustained current, the non-inactivating hASIC3 current starts to be activated when the pH decreases to below pH 6. hASIC3 is an acid sensor and might play an important role in the detection of lasting pH changes in human. We localised the hASIC3 gene to the human chromosome 7q35, 6.4 cRad telomeric from the microsatellite AFMA082XC9.

Acid Sensing Ion Channels↗
PubMed1998

A mammalian two pore domain mechano-gated S-like K+ channel.

Aplysia S-type K+ channels of sensory neurons play a dominant role in presynaptic facilitation and behavioural sensitization. They are closed by serotonin via cAMP-dependent phosphorylation, whereas they are opened by arachidonic acid, volatile general anaesthetics and mechanical stimulation. We have identified a cloned mammalian two P domain K+ channel sharing the properties of the S channel. In addition, the recombinant channel is opened by lipid bilayer amphipathic crenators, while it is closed by cup-formers. The cytoplasmic C-terminus contains a charged region critical for chemical and mechanical activation, as well as a phosphorylation site required for cAMP inhibition.

Amino Acid Sequence↗
PubMed1998

Involvement of IsK-associated K+ channel in heart rate control of repolarization in a murine engineered model of Jervell and Lange-Nielsen syndrome.

The Jervell and Lange-Nielsen (JLN) syndrome affects the human cardioauditory system, associating a profound bilateral deafness with an abnormally long QT interval on the ECG. It results from mutations in KVLQT1 and ISK genes that encode the 2 subunits forming the K+ channel responsible for the cardiac and inner ear slowly activating component of the delayed rectifier K+ current (IKs). A JLN mouse model that presents typical inner ear defects has been created by knocking out the isk gene (isk-/-). This study specifically reports on the cardiac phenotype counterpart, determined in the whole animal and at mRNAs and cellular levels. Surface ECG recordings of isk-/- mice showed a longer QT interval at slow heart rates, a paradoxical shorter QT interval at fast heart rates, and an overall exacerbated QT-heart rate adaptation compared with wild-type (WT) mice. A 300-ms increase in the heart rate cycle length induces a 309+/-21% increase in the QT duration of the WT mice versus a 500+/-50% in isk-/- mice (P<0.001). It is concluded that the isk gene product and/or IKs, when present, blunts the QT adaptation to heart rate variations and that steeper QT-RR relationships reflect a greater susceptibility to arrhythmias in patients lacking IKs.

Aging↗
PubMed1998

Mutations causing neurodegeneration in Caenorhabditis elegans drastically alter the pH sensitivity and inactivation of the mammalian H+-gated Na+ channel MDEG1.

The mammalian degenerin MDEG1 belongs to the nematode degenerin/epithelial Na+ channel superfamily. It is constitutively activated by the same mutations that cause gain-of-function of the Caenorhabditis elegans degenerins and neurodegeneration. ASIC and DRASIC, which were recently cloned, are structural homologues of MDEG1 and behave as H+-gated cation channels. MDEG1 is also a H+-activated Na+ channel, but it differs from ASIC in its lower pH sensitivity and slower kinetics. In addition to the generation of a constitutive current, mutations in MDEG1 also alter the properties of the H+-gated current. Replacement of Gly-430 in MDEG1 by bulkier amino acids, such as Val, Phe, or Thr, drastically increases the H+ sensitivity of the channel (half-maximal pH (pHm) approximately 4.4 for MDEG1, pHm approximately 6.7 for the different mutants). Furthermore, these replacements completely suppress the inactivation observed with the wild-type channel and increase the sensitivity of the H+-gated channel to blockade by amiloride by a factor of 10 without modification of its conductance and ionic selectivity. These results as well as those obtained with other mutants clearly indicate that the region surrounding Gly-430, situated just before the second transmembrane segment, is essential for pH sensitivity and gating.

Amino Acid Substitution↗
PubMed1998

A neuronal two P domain K+ channel stimulated by arachidonic acid and polyunsaturated fatty acids.

TWIK-1, TREK-1 and TASK K+ channels comprise a class of pore-forming subunits with four membrane-spanning segments and two P domains. Here we report the cloning of TRAAK, a 398 amino acid protein which is a new member of this mammalian class of K+ channels. Unlike TWIK-1, TREK-1 and TASK which are widely distributed in many different mouse tissues, TRAAK is present exclusively in brain, spinal cord and retina. Expression of TRAAK in Xenopus oocytes and COS cells induces instantaneous and non-inactivating currents that are not gated by voltage. These currents are only partially inhibited by Ba2+ at high concentrations and are insensitive to the other classical K+ channel blockers tetraethylammonium, 4-aminopyridine and Cs+. A particularly salient feature of TRAAK is that they can be stimulated by arachidonic acid (AA) and other unsaturated fatty acids but not by saturated fatty acids. These channels probably correspond to the functional class of fatty acid-stimulated K+ currents that recently were identified in native neuronal cells but have not yet been cloned. These TRAAK channels might be essential in normal physiological processes in which AA is known to play an important role, such as synaptic transmission, and also in pathophysiological processes such as brain ischemia. TRAAK channels are stimulated by the neuroprotective drug riluzole.

Amino Acid Sequence↗
PubMed1998

A new member of the amiloride-sensitive sodium channel family in Drosophila melanogaster peripheral nervous system.

Amiloride sensitivity is a common characteristic of structurally related cationic channels that are associated with a wide range of physiological functions. In Caenorhabditis elegans, neuronal and muscular degenerins are involved in mechanoperception. In animal epithelia, a Na(+)-selective channel participates in vectorial Na+ transport. In the snail nervous system, an ionotropic receptor for the peptide FMRFamide forms a Na(+)-selective channel. In mammalian brain and/or in sensory neurons, ASIC channels form H(+)-activated cation channels involved in nociception linked to acidosis. We have now cloned a new member of this family from Drosophila melanogaster. The corresponding protein displays low sequence identity with the previously cloned members of the super-family but it has the same structural organization. Its mRNA was detected from late embryogenesis (14-17 hours) and was present in the dendritic arbor subtype of the Drosophila peripheral nervous system multiple dendritic (md) sensory neurons. While the origin and specification of md neurons are well documented, their roles are still poorly understood. They could function as stretch or touch receptors, raising the possibility that this Drosophila gene product, called dmdNaC1, could also be involved in mechanotransduction.

Amiloride↗
PubMed1998

Disruption of mitochondrial respiration inhibits volume-regulated anion channels and provokes neuronal cell swelling.

Hypoxia and inhibitors of mitochondrial respiration impair the regulatory volume decrease (RVD) of cerebellar granule neurons after hypotonic swelling. RVD is linked to the opening of volume-regulated anion channels (VRACs). VRACs are outwardly rectifying, inactivate slowly during maintained depolarization, and are permeable to the cellular organic osmolyte taurine. Channel activation requires nonhydrolytic ATP binding and is not modulated by intracellular ADP. VRAC opening is reversibly depressed by hypoxia and by mitochondrial inhibitors such as oligomycin, rotenone, and antimycin A. These results demonstrate that neuronal VRAC activation and swelling are both tightly linked to cellular energy. Moreover, the findings reported in this work may have a particular significance for inherited mitochondrial human diseases, such as mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), which cause brain swelling and edema.

Animals↗