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M Lazdunski

Publications and source records attributed to M Lazdunski.

At least 235 records · Page 13Linked to original sources
PubMed1991

Cloning, expression, pharmacology and regulation of a delayed rectifier K+ channel in mouse heart.

Neonatal mouse cardiac poly(A)+ mRNA microinjection into Xenopus oocytes directed the expression of a delayed rectifier K+ current. A cDNA encoding this channel, called mIsK, was cloned from a neonatal mouse heart cDNA library whose properties were studied after expression of the complementary RNA in Xenopus oocytes. Among the different known K+ channel blockers, only the class III antiarrhythmic clofilium inhibited mIsK in the 10-100 microM range. The channel was completely insensitive to other antiarrhythmics such as quinine, quinidine, sotalol or amiodarone. mIsK was enhanced by increasing intracellular Ca2+ and by microinjected Ca(2+)-calmodulin dependent protein kinase II. These stimulations were reversed by the calmodulin antagonist W7. Conversely, the phorbol ester PMA, the diacylglycerol analog OAG and microinjected purified protein kinase C inhibited mIsK. This inhibitory effect could be prevented by the protein kinase C inhibitor staurosporine. These results were consistent with the presence of consensus sequences for kinase II and kinase C in the mIsK structure. Cultured newborn mouse ventricular cardiac cells exhibited a delayed rectifier K+ current which had biophysical properties similar to those of cloned mIsK and which was inhibited by clofilium and protein kinase C activators. In situ hybridization experiments revealed that mIsK mRNA was homogeneously distributed in the cardiac tissue. Neonatal mouse heart expressed the most mIsK mRNA compared with various other rat and mouse tissues. Since this K+ channel generates a current which appears to be involved in the control of both the action potential duration and the beating rate, these results suggest an important role for the mIsK channel in cardiac cell physiology and cardiac pathology.

Amino Acid Sequence↗
PubMed1991

Indolizinsulphones. A class of blockers with dual but discriminative effects on L-type Ca2+ channel activity and excitation-contraction coupling in skeletal muscle.

The alpha 1 subunit of the L-type Ca2+ channel plays a dual role in skeletal muscle. It is essential both for L-type Ca2+ channel activity and for the functioning of the voltage-sensor structure that is situated in the triads as a key element for excitation-contraction coupling. This paper shows, with mouse muscle cells in primary culture, that indolizinsulphone SR33557 which has its binding site on the alpha 1 subunit blocks both L-type Ca2+ channel activity and contraction as the more classical 1,4-dihydropyridine blockers. However, unlike other Ca2+ channel blockers, it can pharmacologically discriminate between the two different roles of the alpha 1 subunit. SR33557 inhibition of both contractile and L-type Ca2+ channel activities is very voltage dependent and increases at depolarized potentials. Complete blockade of contraction was observed at low SR33557 concentrations (K0.5 = 20 nM) and was associated with only minor L-type Ca2+ channel blockade (30%). The remaining and major part of the L-type Ca2+ channel activity (70%) was blocked at much higher SR33557 concentrations (K0.5 = 0.6 microM). The results indicate that SR33557 has a much higher affinity for the alpha 1 subunit inserted into the voltage-sensor structure. They also suggest that the voltage-sensor structure, which probably includes most of the total T-tubule alpha 1 subunit, has intrinsic (but relatively small) Ca2+ channel activity.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

A new non-voltage-dependent, epithelial-like Na+ channel in vascular smooth muscle cells.

A new type of Na+ channel was identified in smooth muscle cells of the rat aortic cell line A7r5, and in smooth muscle cells cultured from rat aorta and rat portal vein. The channel is highly selective for Na+ (PNa/PK greater than 11). It is active in cell-attached patches, and independent of the trans-patch membrane potential. The single channel conductance is low (10.7 pS). Two substates were identified. This channel is insensitive to effectors of other types of Na+ channels, such as amiloride (100 microM) or tetrodotoxin (100 microM). It is inhibited by phenamil at high concentrations (greater than 10 microM). The mean open state probability P(O) varied from patch to patch (0.05-0.88). Kinetics analysis reveals a complex behaviour: open times separate in short (tau 1 = 84 ms) and long (tau 2 = 845 ms) openings and closed times separate into short (tau 1 = 60 ms) and long closures (tau 2 = 272-3130 ms). Short openings and long closures are preponderant at a low P(O). Long openings are absent in the presence of phenamil (50 microM) and are unaffected by amiloride (100 microM). Fluctuations of the channel activity in cell-attached patches and the fast disappearance after excision suggest that this channel is under metabolic control. This vascular smooth muscle channel appears to be a potentially important Na+ entry pathway for vascular cells and an amiloride-resistant homologue of the epithelial Na+ channel.

Amiloride↗
PubMed1991

Properties of receptors for neurotoxic phospholipases A2 in different tissues.

A radioiodinated derivative of OS2 (125I-OS2), a neurotoxic monochain phospholipase A2 isolated from taipan venom, was previously found to bind to a specific brain membrane receptor with very high affinity. 125I-OS2 is now used to identify the properties of neurotoxic phospholipase receptors in other tissues. Heart, skeletal muscle, kidney, lung, liver, pancreas, and smooth muscle membranes also contain high-affinity binding sites for toxic phospholipases A2. In most tissues, two different types of receptor sites have been characterized for 125I-OS2 with Kd1 and Kd2 values in the 1-5 pM and the 10-50 pM range respectively. Whereas all receptors are similar in the different tissues in terms of their affinity for 125I-OS2, maximal binding site capacities were very different, varying from 1.3 pmol/mg of protein in brain to 0.01 pmol/mg of protein in pancreas. In brain, heart, and skeletal muscle, receptor densities vary with in vivo development. Affinity labeling experiments have identified the subunit composition of OS2 receptors and indicated that these receptors do not have identical structures in the different tissues. Binding competition studies with OS2 and other toxic phospholipases showed tissue-dependent pharmacological profiles. All these results taken together suggest the existence of a family of receptors for neurotoxic phospholipases.

Animals↗
PubMed1991

Conditional immortalization of normal and dysgenic mouse muscle cells by the SV40 large T antigen under the vimentin promoter control.

We have created new mouse muscle cell lines of an immortalized type, expressing normal differentiation at the myotube stage: sarcomeric organization, functional excitation-contraction coupling, and triadic differentiation. The DNA immortalizing recombinant utilizes a deletion mutant of the regulatory region of the human vimentin promoter controlling the expression of a SV40 thermosensitive large T antigen, in which the small t sequence has been deleted. Skeletal mouse replicative myoblasts synthesized predominantly vimentin. After myoblast fusion the vimentin gene is strongly repressed in multinucleated syncytia. Furthermore, the normal activity of the vimentin promoter in myoblasts is increased in the large T antigen-expressing cells. We observed that continuous and rapid division of myoblasts occurs at permissive temperature, suggesting that immortalization is achieved even though the small t antigen is absent. When fusion is induced by changing media conditions, large T antigen expression is totally repressed by the vimentin promoter. When the temperature is elevated to 39 degrees C, the preexisting large T antigen is inactivated. The resulting myotubes from normal mouse differentiate totally normally as indicated by their morphology, ultrastructure, and electrophysiological properties. Mutant (muscular dysgenesis) immortalized cells express the same properties as mutant primary counterparts with no contraction, no slow Ca2+ current, and no triadic differentiation. These immortalized cell lines are potentially very useful for further pharmacology, transplantation, and cell biology studies. The vimentin promoter control of immortalizing recombinant DNA can be used for any mammalian normal and mutant muscle cell lines.

Animals↗
PubMed1990

Saxitoxin-sensitive Na+ channels: presynaptic localization in cerebellum and hippocampus of neurological mutant mice.

The autoradiographic distribution of saxitoxin (STX) binding sites associated with voltage-sensitive Na+ channel was studied in the cerebellum of neurological weaver (wv/wv), Purkinje cell degeneration (pcd/pcd), nervous (nr/nr) and reeler (rl/rl) mutant mice. The Purkinje cell layer contains the highest density of STX binding sites in normal mice. High densities were observed in the molecular layer. Intermediate and very low densities were present in the granular layer and the white matter respectively. There was an important decrease of grain density in the molecular layer and Purkinje cell layer of wv/wv cerebellum, where a large majority of granular cells had disappeared. In pcd/pcd and nr/nr mutants, a small decrease was observed in Purkinje cell layer where the Purkinje cells had almost all degenerated. In rl/rl mutants where all neuronal cells were malpositioned, the compacted molecular layer contained an increased STX binding sites density. Conversely the labelling of Purkinje cells areas was decreased. The hippocampal formation of rl/rl mutants presents an homogeneous repartition of the Na+ channel protein in contrast with the laminated distribution observed in normal mice. Our autoradiographic data suggest that a major proportion of STX-sensitive Na+ channels are localized in parallel fibers of granular cells and in axons of basket cells in a presynaptic position. In Purkinje cells, the dendritic arborization seems to be devoid of STX binding sites conversely to somata.

Animals↗
PubMed1990

Ca2+ channel blockers inhibit secretory C1-channels in intestinal epithelial cells.

Outwardly rectifying Cl- channels are present in the human colonic cell line (HT29D4). The classical Cl- channel blocker 5-nitro-2(3-phenylpropylamino)benzoate inhibits Cl- channel activity with a K0.5 value of 20 microM. Epithelial Cl- channel activity is inhibited by Ca2+ channel blockers. Phenylalkylamines are the most effective inhibitors. (+/-)Verapamil and (-)desmethoxyverapamil induce flickering and then the complete blockade of Cl- channels recorded from outside-out patches. K0.5 values are 60 microM and 100 microM for (-)desmethoxyverapamil and (+/-)verapamil, respectively. Other classes of L-type Ca2+ channel blockers have also been studied but they are less active.

Adenocarcinoma↗
PubMed1990

Brain ischemia alters the density of binding sites for glibenclamide, a specific blocker of ATP-sensitive K+ channels.

Transient ischemia in normoglycemic animals leads to delayed neuronal damage which is confined to selectively vulnerable regions. In at least one of these, the CA1 sector of the hippocampus, cell death is preceded by neuronal hyperactivity, presumed to be caused by loss of inhibitory control. Hyperglycemic subjects develop postischemic seizures, and show enhanced damage. The ATP-sensitive K+ channel, which may be important in inhibitory control, is the target of antidiabetic sulfonylureas. We determined densities of sulfonylurea binding sites in rat brain after forebrain ischemia. Normoglycemic animals showed a decrease of glibenclamide receptor binding in the CA3 field, hilus and dentate gyrus of the hippocampus after 1 day of recovery. After 4 days of recovery, levels of sulfonylurea binding sites decreased mainly in the CA1 field and in the hilus, as well as in the substantia nigra. After 1 day of recovery, hyperglycemic animals did not show any significant variations of densities of sites compared to control animals. It is proposed that reduction of inhibitory control by ATP-sensitive K+ channels may be associated with delayed neuronal death.

Adenosine Triphosphate↗
PubMed1990

Identification and pharmacological properties of binding sites for the atypical thiazide diuretic, indapamide.

[3H]Indapamide bound to a single class of binding sites in pig renal cortex membranes with a dissociation constant Kd = 35 +/- 13 nM and a binding site density Bmax = 40 +/- 9 pmol/mg of protein. [3H]Indapamide binding was inhibited by the carbonic anhydrase inhibitor, acetazolamide, and by thiazide diuretics with the following rank order of potency: chlorothiazide greater than hydrochlorothiazide approximately metolazone greater than hydroflumethiazide. The effect of the latter drugs to inhibit [3H]indapamide binding was not related to their activity as thiazide diuretics, but was significantly correlated with their inhibitory effect on carbonic anhydrase II. These results suggest that the major renal binding site of [3H]indapamide is a membrane form of carbonic anhydrase. Inhibition of carbonic anhydrase may play a role in the antihypertensive effect of indapamide.

Animals↗
PubMed1990

Sulfonylurea binding sites associated with ATP-regulated K+ channels in the central nervous system: autoradiographic analysis of their distribution and ontogenesis, and of their localization in mutant mice cerebellum.

The localization of a putative ATP-regulated K+ channel in normal rat and neurological mutant mice was studied by light microscopic quantitative autoradiography using a tritiated glibenclamide, an antidiabetic sulfonylurea. Glibenclamide binding sites presented a heterogeneous distribution in the rat central nervous system. Their density was particularly important in substantia nigra reticulata, septohippocampal nucleus, globus pallidus, neocortex, molecular layer of cerebellum, CA3 field and dentate gyrus of hippocampus. Conversely hypothalamic areas, medulla oblongata and spinal cord contained only low amounts of glibenclamide receptors. The ontogenesis of sulfonylurea binding sites was a postnatal phenomenon and seemed to correlate with the maturation of neuronal connectivity. In the cerebellum of neurological mutant mice, the autoradiographic patterns were different to that of wild-type cerebellum. In particular, in the molecular layer of weaver cerebellum, a decrease of 82% of binding site density suggested a presynaptic position of glibenclamide receptors in parallel fibers.

ATP-Binding Cassette Transporters↗
PubMed1990

Identification and purification of a very high affinity binding protein for toxic phospholipases A2 in skeletal muscle.

Oxyuranus scutellatus toxin 1 (OS1) and toxin 2 (OS2) are two monochain phospholipases A2 isolated from the venom of Taipan. Their iodinated derivatives have been used to characterize phospholipase A2 receptors on rabbit skeletal muscle cells in culture. Both ligands recognize one family of binding sites on myotube membranes with a Bmax of 1.9 to 2.2 pmol/mg of protein and dissociation constant values of 7.4 pM for 125I-OS2 and 38 pM for 125I-OS1. Other snake venom phospholipases A2 are able to inhibit 125I-OS2 binding to the muscle receptor. Competition experiments with these unlabeled phospholipases A2 define a pharmacological profile of the muscle receptor very different from the previously described pharmacological profile of the neuronal phospholipase A2 receptors. The number of 125I-OS2 receptors in skeletal muscle cells increases during in vitro cell maturation but there is no clear relation between the increase of Bmax and the fusion of myoblasts into myotubes. The phospholipase A2 binding protein from myotubes has been identified both by cross-linking experiments and by purification studies. It is composed of only one subunit of Mr 180,000.

Affinity Labels↗
PubMed1990

ATP-sensitive K+ channels reveal the effects of intracellular chloride variations on cytoplasmic ATP concentrations and mitochondrial function.

Replacement of intracellular Cl- by impermeant anions, as well as treatment of insulinoma cells by the Cl- channel blocker, NPPB, leads to activation of ATP-dependent K+ (KATP) channels. Activation of KATP channels by C1- substitution is eliminated (i) when intracellular ATP is replaced by non-hydrolyzable ATP analogs, (ii) when the perfusion medium contains an ATP regenerating system, (iii) when the mitochondrial ATPase is blocked by oligomycin. Dinitrophenol and GDP have the same activating effects on KATP channels as NPPB or intracellular Cl- substitution. Our interpretation of the results is that NPPB and intracellular Cl- replacement produce an uncoupling of oxidative phosphorylation by acting on mitochondrial anion channels, which leads to rapid degradation of ATP and to activation of KATP channels. KATP channels are useful sensors of cytoplasmic ATP variations.

Adenosine Triphosphate↗
PubMed1990

Mast cell degranulating peptide induces the expression of the c-fos proto-oncogene in hippocampus.

The intrahippocampal injection of the mast cell degranulating (MCD) peptide, a bee venom component acting on the K+ channel, results in the appearance of the proto-oncogene c-fos mRNA in the ipsi- and contralateral hippocampus of the treated animals without generating convulsions. This MCD-induced transcriptional event is discussed in terms of cellular plasticity since MCD peptide is known to induce long-term potentiation.

Animals↗
PubMed1990

Induction of normal ultrastructure by CGRP treatment in dysgenic myotubes.

The calcitonin gene-related peptide (CGRP) restores an apparent normal ultrastructure in mdg/mdg muscle cells in vitro, including a normal triadic organization which is known to be essential for excitation-contraction (E-C) coupling. However, neither slow L-type Ca2+ channel activity nor E-C coupling, which are absent in mdg/mdg muscle, were re-established. These observations suggest a potential role of CGRP (and also of cAMP as the intracellular messenger) in the morphological development of the muscle fiber.

Animals↗
PubMed1990

Regional expression of a MCD-peptide and dendrotoxin I-sensitive voltage-dependent potassium channel in rat brain.

In situ hybridization histochemistry has been used to analyze the regional expression of a class of voltage-dependent K+ channel that is sensitive to two polypeptide toxins (MCD peptide and dendrotoxin I) that produce spectacular effects on brain function. A heterogeneous expression of this K+ channel was observed throughout the brain. High mRNA contents were observed in the granule cells of the gyrus dentatus as well as in pyramidal cells of the Ammon horn (CA3 greater than CA1) and in the cerebellum. Conversely, low levels of expression were found in basal ganglia (caudate putamen, globus pallidus, and ventral pallidum).

Animals↗
PubMed1990

Leiurotoxin I (scyllatoxin), a peptide ligand for Ca2(+)-activated K+ channels. Chemical synthesis, radiolabeling, and receptor characterization.

Leiurotoxin I (scyllatoxin) is a 31-amino acid polypeptide from the venom of the scorpion Leiurus quinquestriatus hebraeus which has been previously isolated and sequenced by others. This paper reports (i) the total synthesis of this scorpion neurotoxin as well as some aspects of its structure-function relationships; (ii) the synthesis of the analog [Tyr2]leiurotoxin I (scyllatoxin) that has been monoiodinated at high specific radioactivity (2000 Ci/mmol) and has served for the characterization of the properties of 125I-[Tyr2]leiurotoxin I binding sites (Kd = 80 pM, molecular mass of 27 and 57 kDa for two polypeptides in the leiurotoxin I binding protein); (iii) the similarity of physiological actions between leiurotoxin I and apamin. Both toxins contract Taenia coli previously relaxed with epinephrine, both toxins block the after-hyperpolarization due to Ca2(+)-activated K+ channel activity in muscle cells in culture; (iv) the probable identity of binding sites for apamin and leiurotoxin I. In spite of a different chemical structure apamin competitively inhibits 125I-[Tyr2] leiurotoxin I binding and vice versa. Moreover, the peculiar effects of K+ on 125I-[Tyr2]leiurotoxin I binding are identical to those previously observed for 125I-apamin binding.

Amino Acid Sequence↗
PubMed1990

Glucose, sulfonylureas, and neurotransmitter release: role of ATP-sensitive K+ channels.

Sulfonylurea-sensitive adenosine triphosphate (ATP)-regulated potassium (KATP) channels are present in brain cells and play a role in neurosecretion at nerve terminals. KATP channels in substantia nigra, a brain region that shows high sulfonylurea binding, are inactivated by high glucose concentrations and by antidiabetic sulfonylureas and are activated by ATP depletion and anoxia. KATP channel inhibition leads to activation of gamma-aminobutyric acid (GABA) release, whereas KATP channel activation leads to inhibition of GABA release. These channels may be involved in the response of the brain to hyper- and hypoglycemia (in diabetes) and ischemia or anoxia.

Adenosine Triphosphate↗