Biomedical subjects

F Lesage

Publications and source records attributed to F Lesage.

At least 19 recordsLinked to original sources

PubMed2003

Thrombocytopenia and Plasmodium falciparum malaria in children with different exposures.

We studied thrombocytopenia during acute Plasmodium falciparum malaria in 64 traveller children from Paris (France), 85 children from Dakar (Senegal) with an intermittent exposure (69 with severe attack or cerebral malaria), and 81 children from Libreville (Gabon) with a perennial exposure (43 with severe attack or cerebral malaria). Initial thrombocytopenia was present in 43-58% of children with P falciparum malaria but was not more frequent in severe outcome or cerebral malaria. Low parasitaemia may lead to the misdiagnosis of malaria and delayed treatment when there is associated thrombocytopenia

Acute Disease↗

PubMed2003

Expression and localization of TREK-1 K+ channels in human odontoblasts.

During tooth development, odontoblasts are the cells that form dentin and possibly mediate early stages of sensory processing in teeth. It is suggested that ion channels assist in these events. Indeed, mechanosensitive potassium currents, transducing mechanical stimuli into electrical cell signals, have been previously recorded in the human odontoblast cell membrane. Here, we show by RT-PCR that the mechanosensitive potassium channel TREK-1 (a member of the two-pore-domain potassium channel family) is overexpressed in these cultured cells compared with pulp cells in vitro. In situ hybridization showed that transcripts are detected in the odontoblast layer in vivo. The use of antibodies shows that TREK-1 is strongly expressed in the membrane of coronal odontoblasts and absent in the root. This distribution is related to the spatial distribution of nerve endings identified by labeling of the low-affinity nerve growth factor (NGF) receptor (p75(NTR)). These results demonstrate the expression of TREK-1 in human odontoblasts in vitro and in vivo.

Cell Membrane↗

PubMed2002

Direct interaction with a nuclear protein and regulation of gene silencing by a variant of the Ca2+-channel beta 4 subunit.

The beta subunits of voltage-gated Ca(2+) channels are known to be regulators of the channels' gating properties. Here we report a striking additional function of a beta subunit. Screening of chicken cochlear and brain cDNA libraries identified beta(4c), a short splice variant of the beta(4) subunit. Although beta(4c) occurs together with the longer isoforms beta(4a) or beta(4b) in the brain, eye, heart, and lung, the cochlea expresses exclusively beta(4c). The association of beta(4c) with the Ca(2+)-channel alpha(1) subunit has slight but significant effects on the kinetics of channel activation and inactivation. Yeast two-hybrid and biochemical assays revealed that beta(4c) interacts directly with the chromo shadow domain of chromobox protein 2heterochromatin protein 1gamma (CHCB2HP1gamma), a nuclear protein involved in gene silencing and transcriptional regulation. Coexpression of this protein specifically recruits beta(4c) to the nuclei of mammalian cells. Furthermore, beta(4c) but not beta(4a) dramatically attenuates the gene-silencing activity of chromobox protein 2heterochromatin protein 1gamma. The beta(4c) subunit is therefore a multifunctional protein that not only constitutes a portion of the Ca(2+) channel but also regulates gene transcription.

Alternative Splicing↗

PubMed2002

RIM binding proteins (RBPs) couple Rab3-interacting molecules (RIMs) to voltage-gated Ca(2+) channels.

Ca(2+) influx through voltage-gated channels initiates the exocytotic fusion of synaptic vesicles to the plasma membrane. Here we show that RIM binding proteins (RBPs), which associate with Ca(2+) channels in hair cells, photoreceptors, and neurons, interact with alpha(1D) (L type) and alpha(1B) (N type) Ca(2+) channel subunits. RBPs contain three Src homology 3 domains that bind to proline-rich motifs in alpha(1) subunits and Rab3-interacting molecules (RIMs). Overexpression in PC12 cells of fusion proteins that suppress the interactions of RBPs with RIMs and alpha(1) augments the exocytosis triggered by depolarization. RBPs may regulate the strength of synaptic transmission by creating a functional link between the synaptic-vesicle tethering apparatus, which includes RIMs and Rab3, and the fusion machinery, which includes Ca(2+) channels and the SNARE complex.

Animals↗

PubMed2001

A TREK-1-like potassium channel in atrial cells inhibited by beta-adrenergic stimulation and activated by volatile anesthetics.

Many members of the two-pore-domain potassium (K(+)) channel family have been detected in the mammalian heart but the endogenous correlates of these channels still have to be identified. We investigated whether I(KAA), a background K(+) current activated by negative pressure (stretch) and by arachidonic acid (AA) and sensitive to intracellular acidification, could be the native correlate of TREK-1 in adult rat atrial cells. Using the inside-out configuration of the patch-clamp technique, we found that I(KAA), like TREK-1, was outwardly rectifying in physiological K(+) conditions, with a conductance of 41 pS at +50 mV. Like TREK-1, I(KAA) was reversibly activated by clinical concentrations of volatile anesthetics (in mmol/L, chloroform 0.18, halothane 0.11, and isoflurane 0.69). In cell-attached experiments, I(KAA) was inhibited by chlorophenylthio-cAMP (500 micromol/L) and also by stimulation of beta-adrenergic receptors with isoproterenol (1 micromol/L). In addition, TREK-1 mRNAs were detected in all cardiac tissues, and the TREK-1 protein was immunolocalized in isolated atrial myocytes. Such a background potassium channel might contribute to the positive inotropic effects produced by beta-adrenergic stimulation of the heart. It might also be involved in the regulation of the atrial natriuretic peptide secretion.

Adrenergic beta-Agonists↗

PubMed2001

Genomic and functional characteristics of novel human pancreatic 2P domain K(+) channels.

We isolated three novel 2P domain K(+) channel subunits from human. The first two subunits, TALK-1 and TALK-2, are distantly related to TASK-2. Their genes form a tight cluster of 25 kb on chromosome 6p21.1-p21.2. The corresponding channels produce quasi-instantaneous and non-inactivating currents that are activated at alkaline pHs. These currents are sensitive to Ba(2+), quinine, quinidine, chloroform, halothane, and isoflurane but are not affected by TEA, 4-AP, Cs(+), arachidonic acid, hypertonic solutions, agents activating protein kinases C and A, changes of internal Ca(2+) concentrations, and by activation of G(i) and G(q) proteins. TALK-1 is exclusively expressed in the pancreas. TALK-2 is mainly expressed in the pancreas, but is also expressed at a lower level in liver, placenta, heart, and lung. We also cloned a third subunit, named hTHIK-2 which is present in many tissues with high levels again in the pancreas but which could not be functionally expressed.

Amino Acid Sequence↗

PubMed2000

Human TREK2, a 2P domain mechano-sensitive K+ channel with multiple regulations by polyunsaturated fatty acids, lysophospholipids, and Gs, Gi, and Gq protein-coupled receptors.

Mechano-sensitive and fatty acid-activated K(+) belong to the structural class of K(+) channel with two pore domains. Here, we report the isolation and the characterization of a novel member of this family. This channel, called TREK2, is closely related to TREK1 (78% of homology). Its gene is located on chromosome 14q31. TREK2 is abundantly expressed in pancreas and kidney and to a lower level in brain, testis, colon, and small intestine. In the central nervous system, TREK2 has a widespread distribution with the highest levels of expression in cerebellum, occipital lobe, putamen, and thalamus. In transfected cells, TREK2 produces rapidly activating and non-inactivating outward rectifier K(+) currents. The single-channel conductance is 100 picosiemens at +40 mV in 150 mm K(+). The currents can be strongly stimulated by polyunsaturated fatty acid such as arachidonic, docosahexaenoic, and linoleic acids and by lysophosphatidylcholine. The channel is also activated by acidification of the intracellular medium. TREK2 is blocked by application of intracellular cAMP. As with TREK1, TREK2 is activated by the volatile general anesthetics chloroform, halothane, and isoflurane and by the neuroprotective agent riluzole. TREK2 can be positively or negatively regulated by a variety of neurotransmitter receptors. Stimulation of the G(s)-coupled receptor 5HT4sR or the G(q)-coupled receptor mGluR1 inhibits channel activity, whereas activation of the G(i)-coupled receptor mGluR2 increases TREK2 currents. These multiple types of regulations suggest that TREK2 plays an important role as a target of neurotransmitter action.

Amino Acid Sequence↗

PubMed2000

TREK-1 is a heat-activated background K(+) channel.

Peripheral and central thermoreceptors are involved in sensing ambient and body temperature, respectively. Specialized cold and warm receptors are present in dorsal root ganglion sensory fibres as well as in the anterior/preoptic hypothalamus. The two-pore domain mechano-gated K(+) channel TREK-1 is highly expressed within these areas. Moreover, TREK-1 is opened gradually and reversibly by heat. A 10 degrees C rise enhances TREK-1 current amplitude by approximately 7-fold. Prostaglandin E2 and cAMP, which are strong sensitizers of peripheral and central thermoreceptors, reverse the thermal opening of TREK-1 via protein kinase A-mediated phosphorylation of Ser333. Expression of TREK-1 in peripheral sensory neurons as well as in central hypothalamic neurons makes this K(+) channel an ideal candidate as a physiological thermoreceptor.

Animals↗

PubMed2000

Cloning and expression of human TRAAK, a polyunsaturated fatty acids-activated and mechano-sensitive K(+) channel.

The two P domain hTRAAK K(+) channel has been cloned from human brain. hTRAAK cDNA encodes a 393 amino acid polypeptide with 88% of homology with its mouse counterpart. The hTRAAK gene has been mapped to chromosome 11q13 and the study of its organization indicates that the hTRAAK open reading frame is contained in six exons. hTRAAK is expressed abundantly in brain and placenta. In COS cells, hTRAAK currents are K(+)-selective, instantaneous and non-inactivating. These currents are insensitive to the classical K(+) channels blockers 4-aminopyridine, tetraethylammonium, barium and quinidine, but are strongly stimulated by application of arachidonic acid as well as other polyunsaturated fatty acids. hTRAAK can also be activated by a stretch of the membrane.

Amino Acid Sequence↗

PubMed2000

Lysophospholipids open the two-pore domain mechano-gated K(+) channels TREK-1 and TRAAK.

The two-pore (2P) domain K(+) channels TREK-1 and TRAAK are opened by membrane stretch as well as arachidonic acid (AA) (Patel, A. J., Honoré, E., Maingret, F., Lesage, F., Fink, M., Duprat, F., and Lazdunski, M. (1998) EMBO J. 17, 4283-4290; Maingret, F., Patel, A. J., Lesage, F., Lazdunski, M., and Honoré, E. (1999) J. Biol. Chem. 274, 26691-26696; Maingret, F., Fosset, M., Lesage, F., Lazdunski, M. , and Honoré, E. (1999) J. Biol. Chem. 274, 1381-1387. We demonstrate that lysophospholipids (LPs) and platelet-activating factor also produce large specific and reversible activations of TREK-1 and TRAAK. LPs activation is a function of the size of the polar head and length of the acyl chain but is independent of the charge of the molecule. Bath application of lysophosphatidylcholine (LPC) immediately opens TREK-1 and TRAAK in the cell-attached patch configuration. In excised patches, LPC activation is lost, whereas AA still produces maximal opening. The carboxyl-terminal region of TREK-1, but not the amino terminus and the extracellular loop M1P1, is critically required for LPC activation. LPC activation is indirect and may possibly involve a cytosolic factor, whereas AA directly interacts with either the channel proteins or the bilayer and mimics stretch. Opening of TREK-1 and TRAAK by fatty acids and LPs may be an important switch in the regulation of synaptic function and may also play a protective role during ischemia and inflammation.

Amiloride↗

PubMed2000

Axonal transport of TREK and TRAAK potassium channels in rat sciatic nerves.

The recent cloning, functional expression and brain localization of two new potassium channels, TREK and TRAAK, led us to examine whether both channels are present in peripheral nerves and can move along axons by means of axonal transport mechanisms. Using specific antibodies directed against TREK and TRAAK peptides, we found that immunoreactivity for both potassium channels accumulates above and below a ligature in rat sciatic nerves. The process was rapid and bidirectional suggesting that the channels are associated with vesicles. This represents the first report on the axonal transport of potassium channels.

Animals↗

PubMed2000

Immunolocalization of the arachidonic acid and mechanosensitive baseline traak potassium channel in the nervous system.

TRAAK is the sole member of the emerging class of 2P domain K+ channels to be exclusively expressed in neuronal cells. TRAAK produces baseline K+ currents which are strongly stimulated by arachidonic acid and by mechanical stretch, and which are insensitive to the classical K+ channel blockers tetraethylammonium, Ba2+, and Cs+. This report describes the immunolocalization of TRAAK in brain, spinal cord, and retina of the adult mouse. The most striking finding is the widespread distribution of the TRAAK immunoreactivity, with a prominent staining of the cerebellar cortex, neocortex, hippocampus, dentate gyrus, subiculum, the dorsal hippocampal commissure, thalamus, caudate-putamen, olfactory bulb, and several nuclei in the brainstem. Virtually all neurons express TRAAK, and the highest immunoreactivity was seen in soma, and to a lesser degree in axons and/or dendrites in most areas in brain and spinal cord. In the retina, the TRAAK protein is concentrated to the soma of ganglion cells and to the dendrites of all other neurons. Taken together, these results show a wide distribution of TRAAK, a mechanosensitive and arachidonic acid-stimulated neuron-specific baseline K+ channel, in brain, spinal cord and retina.

Animals↗

PubMed2000

Molecular and functional properties of two-pore-domain potassium channels.

The two-pore-domain K(+) channels, or K(2P) channels, constitute a novel class of K(+) channel subunits. They have four transmembrane segments and are active as dimers. The tissue distribution of these channels is widespread, and they are found in both excitable and nonexcitable cells. K(2P) channels produce currents with unusual characteristics. They are quasi-instantaneous and noninactivating, and they are active at all membrane potentials and insensitive to the classic K(+) channel blockers. These properties designate them as background K(+) channels. They are expected to play a major role in setting the resting membrane potential in many cell types. Another salient feature of K(2P) channels is the diversity of their regulatory mechanisms. The weak inward rectifiers TWIK-1 and TWIK-2 are stimulated by activators of protein kinase C and decreased by internal acidification, the baseline TWIK-related acid-sensitive K(+) (TASK)-1 and TASK-2 channels are sensitive to external pH changes in a narrow range near physiological pH, and the TWIK-related (TREK)-1 and TWIK-related arachidonic acid-stimulated K(+) (TRAAK) channels are the first cloned polyunsaturated fatty acids-activated and mechanogated K(+) channels. The recent demonstration that TASK-1 and TREK-1 channels are activated by inhalational general anesthetics, and that TRAAK is activated by the neuroprotective agent riluzole, indicates that this novel class of K(+) channels is an interesting target for new therapeutic developments.

Animals↗

PubMed2000

TASK (TWIK-related acid-sensitive K+ channel) is expressed in glomerulosa cells of rat adrenal cortex and inhibited by angiotensin II.

The present study was conducted to explore the possible contribution of a recently described leak K+ channel, TASK (TWIK-related acid-sensitive K+ channel), to the high resting K+ conductance of adrenal glomerulosa cells. Northern blot analysis showed the strongest TASK message in adrenal glomerulosa (capsular) tissue among the examined tissues including heart and brain. Single-cell PCR demonstrated TASK expression in glomerulosa cells. In patch-clamp experiments performed on isolated glomerulosa cells the inward current at -100 mV in 30 mM [K+] (reflecting mainly potassium conductance) was pH sensitive (17+/-2% reduction when the pH changed from 7.4 to 6.7). In Xenopus oocytes injected with mRNA prepared from adrenal glomerulosa tissue the expressed K+ current at -100 mV was virtually insensitive to tetraethylammonium (3 mM) and 4-aminopyridine (3 mM). Ba2+ (300 microM) and Cs+ (3 mM) induced voltage-dependent block. Lidocaine (1 mM) and extracellular acidification from pH 7.5 to 6.7 inhibited the current (by 28% and 16%, respectively). This inhibitory profile is similar (although it is not identical) to that of TASK expressed by injecting its cRNA. In oocytes injected with adrenal glomerulosa mRNA, TASK antisense oligonucleotide reduced significantly the expression of K+ current at -100 mV, while the sense oligonucleotide failed to have inhibitory effect. Application of angiotensin II (10 nM) both in isolated glomerulosa cells and in oocytes injected with adrenal glomerulosa mRNA inhibited the K+ current at -100 mV. Similarly, in oocytes coexpressing TASK and ATla angiotensin II receptor, angiotensin II inhibited the TASK current. These data together indicate that TASK contributes to the generation of high resting potassium permeability of glomerulosa cells, and this background K+ channel may be a target of hormonal regulation.

4-Aminopyridine↗

PubMed2000

The neuroprotective agent riluzole activates the two P domain K(+) channels TREK-1 and TRAAK.

Riluzole (RP 54274) is a potent neuroprotective agent with anticonvulsant, sedative, and anti-ischemic properties. It is currently used in the treatment of amyotrophic lateral sclerosis. This article reports that riluzole is an activator of TREK-1 and TRAAK, two important members of a new structural family of mammalian background K(+) channels with four transmembrane domains and two pore regions. Whereas riluzole activation of TRAAK is sustained, activation of TREK-1 is transient and is followed by an inhibition. The inhibitory process is attributable to an increase of the intracellular cAMP concentration by riluzole that produces a protein kinase A-dependent inhibition of TREK-1. Mutants of TREK-1 lacking the Ser residue where the kinase A phosphorylation takes place are activated in a sustained manner by riluzole. TRAAK is permanently activated by riluzole because, unlike TREK-1, it lacks the negative regulation by cAMP.

Animals↗

PubMed1999

Mechano- or acid stimulation, two interactive modes of activation of the TREK-1 potassium channel.

TREK-1 is a member of the novel structural class of K(+) channels with four transmembrane segments and two pore domains in tandem (1,2). TREK-1 is opened by membrane stretch and arachidonic acid. It is also an important target for volatile anesthetics (2,3). Here we show that internal acidification opens TREK-1. Indeed, lowering pH(i) shifts the pressure-activation relationship toward positive values and leads to channel opening at atmospheric pressure. The pH(i)-sensitive region in the carboxyl terminus of TREK-1 is the same that is critically involved in mechano-gating as well as arachidonic acid activation. A convergence, which is dependent on the carboxyl terminus, occurs between mechanical, fatty acids and acidic stimuli. Intracellular acidosis, which occurs during brain and heart ischemia, will induce TREK-1 opening with subsequent K(+) efflux and hyperpolarization.

Acids↗

PubMed1999

A novel mammalian lithium-sensitive enzyme with a dual enzymatic activity, 3'-phosphoadenosine 5'-phosphate phosphatase and inositol-polyphosphate 1-phosphatase.

We report the molecular cloning in Rattus norvegicus of a novel mammalian enzyme (RnPIP), which shows both 3'-phosphoadenosine 5'-phosphate (PAP) phosphatase and inositol-polyphosphate 1-phosphatase activities. This enzyme is the first PAP phosphatase characterized at the molecular level in mammals, and it represents the first member of a novel family of dual specificity enzymes. The phosphatase activity is strictly dependent on Mg2+, and it is inhibited by Ca2+ and Li+ ions. Lithium chloride inhibits the hydrolysis of both PAP and inositol-1,4-bisphosphate at submillimolar concentration; therefore, it is possible that the inhibition of the human homologue of RnPIP by lithium ions is related to the pharmacological action of lithium. We propose that the PAP phosphatase activity of RnPIP is crucial for the function of enzymes sensitive to inhibition by PAP, such as sulfotransferase and RNA processing enzymes. Finally, an unexpected connection between PAP and inositol-1,4-bisphosphate metabolism emerges from this work.

Amino Acid Sequence↗

PubMed1999

Cloning of a new mouse two-P domain channel subunit and a human homologue with a unique pore structure.

Mouse KCNK6 is a new subunit belonging to the TWIK channel family. This 335-amino acid polypeptide has four transmembrane segments, two pore-forming domains, and a Ca2+-binding EF-hand motif. Expression of KCNK6 transcripts is principally observed in eyes, lung, stomach and embryo. In the eyes, immunohistochemistry reveals protein expression only in some of the retina neurons. Although KCNK6 is able to dimerize as other functional two-P domain K+ channels when it is expressed in COS-7 cells, it remains in the endoplasmic reticulum and is unable to generate ionic channel activity. Deletions, mutations, and chimera constructions suggest that KCNK6 is not an intracellular channel but rather a subunit that needs to associate with a partner, which remains to be discovered, in order to reach the plasma membrane. A closely related human KCNK7-A subunit has been cloned. KCNK7 displays an intriguing GLE sequence in its filter region instead of the G(Y/F/L)G sequence, which is considered to be the K+ channel signature. This subunit is alternatively spliced and gives rise to the shorter forms KCNK7-B and -C. None of the KCNK7 structures can generate channel activity by itself. The KCNK7 gene is situated on chromosome 11, in the q13 region, where several candidate diseases have been identified.

Amino Acid Sequence↗