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M Lazdunski

Publications and source records attributed to M Lazdunski.

At least 19 recordsLinked to original sources
PubMed1992

Characterization and partial purification from pheochromocytoma cells of an endogenous equivalent of scyllatoxin, a scorpion toxin which blocks small conductance Ca(2+)-activated K+ channels.

This work describes the partial purification of a heat-stable peptide which has the same properties as the scorpion toxin, scyllatoxin, a specific blocker of one class of Ca(2+)-activated K+ channels: (i) it competes with [125I]apamin for binding to the same site, (ii) like apamin and scyllatoxin, it blocks the after-potential hyperpolarization in skeletal muscle cells in culture, (iii) like apamin and scyllatoxin, it contracts guinea-pig taenia coli relaxed by epinephrine, (iv) it cross-reacts with antibodies raised against scyllatoxin but not with antibodies raised against apamin.

Animals↗
PubMed1992

Effects of the level of mRNA expression on biophysical properties, sensitivity to neurotoxins, and regulation of the brain delayed-rectifier K+ channels Kv1.2.

Injection of 0.2 ng of cRNA encoding the brain Kv1.2 channel into Xenopus oocytes leads to the expression of a very slowly inactivating K+ current. Inactivation is absent in oocytes injected with 20 ng of cRNA although activation remains unchanged. Low cRNA concentrations generate a channel which is sensitive to dendrotoxin I (IC50 = 2 nM at 0.2 ng of cRNA/oocyte) and to less potent analogs of this toxin from Dendroaspis polylepis venom. A good correlation is found between blockade of the K+ current and binding of the different toxins to rat brain membranes. High cRNA concentrations generate another form of the K+ channel which is largely insensitive to dendrotoxin I (IC50 = 200 nM at 20 ng of cRNA per oocyte). At low cRNA concentrations, the expressed Kv1.2 channel is also blocked by other polypeptide toxins such as MCD peptide (IC50 = 20 nM), charybdotoxin (IC50 = 50 nM), and beta-bungarotoxin (IC50 = 50 nM), which bind to distinct and allosterically related sites on the channel protein. The pharmacologically distinct type of K+ channel expressed at high cRNA concentrations (20 ng of cRNA/oocyte) is nearly totally resistant to 100 nM MCD peptide and hardly altered by charybdotoxin and beta-bungarotoxin at concentrations as high as 1 microM. Both at low and at high cRNA concentrations, the expressed Kv1.2 channel is blocked by an increase in intracellular Ca2+ from the inositol trisphosphate sensitive pools and by the phorbol ester PMA that activates protein kinase C.

Allosteric Site↗
PubMed1992

Developmental expression of voltage-sensitive K+ channels in mouse skeletal muscle and C2C12 cells.

The developmental expression of voltage-sensitive K+ channels was analyzed by Northern blot in mouse skeletal muscle. Of nine Shaker-like genes studied, eight are expressed in this mammalian muscle. Their expression is differentially regulated during development. The mouse cell line C2C12 has been used to study expression of voltage-sensitive K+ channels during in vitro myotube differentiation. Different voltage-sensitive K+ channel messages are also expressed in these cells which display a pattern of expression depending upon the differentiation stage. The message for the very peculiar K+ channel of IsK type could only be detected by polymerase chain reaction on skeletal muscle mRNA.

Animals↗
PubMed1992

Effectors of ATP-sensitive K+ channels inhibit the regulatory effects of somatostatin and GH-releasing factor on growth hormone secretion.

Somatostatin inhibition of growth hormone (GH) secretion from adenohypophysis cells in culture was antagonized by the antidiabetic sulfonylurea glipizide (K0.5 = 10 +/- 5 nM). Although all cells that hyperpolarize with somatostatin have ATP-sensitive K+ channels, the antagonistic actions of the hormone and of the antidiabetic drug are due to effects on different types of K+ channels. Diazoxide, an opener of ATP-sensitive K+ channels, abolished the increase of intracellular Ca2+ provoked by growth hormone releasing factor (GRF) and induced inhibition of GRF stimulated GH secretion (K0.5 = 138 microM). This inhibition by diazoxide was largely suppressed by glipizide which blocked the ATP-sensitive K+ channels opened by diazoxide. In summary, hormonal activation of GH secretion is inhibited by openers of ATP-sensitive K+ channels, while hormonal inhibition of GH secretion is suppressed by blockers of ATP-sensitive K+ channels.

Adenosine Triphosphate↗
PubMed1992

A new member of the natriuretic peptide family is present in the venom of the green mamba (Dendroaspis angusticeps).

This paper describes the purification, sequence, and biological properties of a 38-amino acid residue peptide from the venom of Dendroaspis angusticeps which shared important sequence homologies with natriuretic peptides. Dendroaspis natriuretic peptide (DNP) relaxed aortic strips that had been contracted by 40 mM KCl with a potency (K0.5 = 20 nM) similar to that of atrial natriuretic peptide (ANP) and larger than that of C type natriuretic peptide (CNP). The relaxing actions of ANP and DNP (both at 100 nM) were mutually exclusive. Bovine aortic endothelial cells responded to ANP (K0.5 = 3 nM) and DNP (K0.5 = 3 nM) but not to CNP by a large activation of guanylate cyclase. Rat aortic myocytes showed larger cGMP responses to CNP (K0.5 = 10 nM) than to ANP or DNP (K0.5 = 100 nM). Finally, DNP completely prevented the specific 125I-ANP binding to clearance receptors in cultured aortic myocytes with a potency (Kd = 10 nM) that was less than that of ANP (Kd = 0.3 nM). It is concluded that DNP is a new member of the family of natriuretic peptides and that it recognizes ANPA receptors and clearance, ANPc receptors, but not CNP-specific ANPB receptors.

Amino Acid Sequence↗
PubMed1992

ATP/ADP binding sites are present in the sulfonylurea binding protein associated with brain ATP-sensitive K+ channels.

Covalent labeling of nucleotide binding sites of the purified sulfonylurea receptor has been carried out with alpha-32P-labeled oxidized ATP. The main part of 32P incorporation is in the 145-kDa glycoprotein that has been previously shown to be the sulfonylurea binding protein (Bernardi et al., 1988). ATP and ADP protect against this covalent labeling with K0.5 values of 100 microM and 500 microM, respectively. Non-hydrolyzable analogs of ATP also inhibit 32P incorporation. Interactions between nucleotide binding sites and sulfonylurea binding sites have then been observed. AMP-PNP, a nonhydrolyzable analog of ATP, produces a small inhibition of [3H]glibenclamide binding (20-25%) which was not influenced by Mg2+. Conversely, ADP, which also produced a small inhibition (20%) in the absence of Mg2+, produced a large inhibition (approximately 80%) in the presence of Mg2+. This inhibitory effect of the ADP-Mg2+ complex was observed with a K0.5 value of 100 +/- 40 microM. All the results taken together indicate that ATP and ADP-Mg2+ binding sites that control the activity of KATP channels are both present on the same subunit that bears the receptors for antidiabetic sulfonylureas.

ATP-Binding Cassette Transporters↗
PubMed1992

Behavioral effects of modulators of ATP-sensitive K+ channels in the rat dorsal pallidum.

The effects of the potent ATP-sensitive K+ channel blocker glipizide were measured on the locomotor activity of rats after bilateral intracerebral administration into the dorsal pallidum. Glipizide (10 pmol) was found to reduce spontaneous locomotor activity measured during the night cycle of the rats, whereas the ATP-sensitive K+ channel activator (-)-cromakalim (5 fmol) enhanced spontaneous locomotor activity. Glipizide (0.5, 2.5 and 10 pmol) was also found to depress noticeably d-amphetamine-induced locomotor activity (1 mg/kg s.c.). These results are in agreement with the idea that ATP-dependent potassium channels within the dorsal pallidum are involved in controlling motor activity in the rat.

Adenosine Triphosphate↗
PubMed1992

Regulation of a major cloned voltage-gated K+ channel from human T lymphocytes.

When expressed into Xenopus oocytes, HLK3 K+ channel (Kv1-3) induced a slowly inactivating voltage-dependent K+ current. We have studied the modulation of this K+ current by co-expressing a cloned 5-HT2 receptor together with HLK3 K+ channel protein. Application of 5-HT caused a long-lasting inhibition of the voltage-gated K+ current. This inhibitory modulation was mimicked by intracellular injection of inositol triphosphate or Ca2+, as well as by incubation with phorbol esters or diacylglycerol analogs. Oocytes pretreatment with staurosporine and EGTA fully prevented 5-HT inhibitory action. Elevation of cAMP and cGMP levels into oocytes did not produce any detectable effect on the current recorded in the absence or the presence of 5-HT. These data suggest that the second messengers generated by phospholipase C activation may be important modulators of HLK3 K+ channels in the immune and the central nervous systems.

Animals↗
PubMed1992

Opening of glibenclamide-sensitive K+ channels in follicular cells promotes Xenopus oocyte maturation.

The vasorelaxing K+ channel opener P1060 (a pinacidil analog), gonadotropins, and cAMP were shown to activate a glibenclamide-sensitive 86Rb+ efflux from fully grown follicle-enclosed Xenopus oocytes. Glibenclamide-sensitive K+ channels are located in follicular cells. Glibenclamide (i) depressed the gonadotropin- but not the progesterone-induced maturation and (ii) did not significantly modify progesterone production in oocytes exposed to Xenopus gonadotropin. In follicle-enclosed oocytes, the opener P1060 very significantly enhanced the oocyte sensitivity to progesterone. This increased sensitivity to the hormone induced by the K+ channel opener was reversed by glibenclamide. Thus these results suggest that the opening of glibenclamide-sensitive K+ channels in follicular cells by gonadotropins (and other activators of this channel) induces a hyperpolarization in the oocyte that greatly facilitates maturation by increasing the oocyte sensitivity to progesterone.

Animals↗
PubMed1992

ATP-sensitive K+ channels in insulinoma cells are activated by nonesterified fatty acids.

Both 86Rb+ efflux experiments and electrophysiological studies have shown that arachidonic acid and other nonesterified fatty acids activate ATP-sensitive K+ channels in insulinoma cells (HIT-T15). Activation was observed with arachidonic, oleic, linoleic, and docosahexaenoic acid but not with myristic, stearic, and elaidic acids. Fatty acid activation of ATP-sensitive K+ channels was blocked by antidiabetic sulfonylureas such as glibenclamide. The activating effect of arachidonic acid was unaltered by indomethacin and by nordihydroguaiaretic acid, indicating that it is not due to metabolites of arachidonic acid via cyclooxygenase or lipoxygenase pathways. Moreover, the nonmetabolizable analogue of arachidonic acid, eicosatetraynoic acid, was an equally potent activator. Activation of ATP-sensitive K+ channels by fatty acids was potentiated by diacylglycerol and was inhibited by calphostin C, an inhibitor of protein kinase C. These findings indicate that fatty acid activation of ATP-sensitive K+ channels is most likely due to the participation of arachidonic acid (and other fatty acid)-activated protein kinase C isoenzymes. Activation of ATP-sensitive K+ channels by nonesterified fatty acids is not involved in the control of insulin secretion since arachidonic acid stimulates insulin secretion from insulinoma cells instead of inhibiting it.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1992

Receptor-mediated regulation of IsK, a very slowly activating, voltage-dependent K+ channel in Xenopus oocytes.

Expression of IsK in Xenopus oocytes has been obtained in 2 ways: (i) by injection of cardiac polyA+ RNA from neonatal mouse heart; (ii) by injection of a cRNA synthesized in vitro. It was observed that polyA+ RNA not only directs the expression of the IsK channel but also contains purinergic P2 and endothelin receptors. Stimulation of these receptors, that produce intracellular Ca2+ increase together with diacylglycerol production activating protein kinase C, increases IsK activity. The same type of results and the same conclusions were obtained by co-injecting cRNA's corresponding to the 5-HT2 receptor and the IsK channel into oocytes. This stimulatory effect was shown to be due to Ca2+ via a calmodulin-dependent kinase process. Conversely, activation of protein kinase C pathway alone by phorbol esters leads to inhibition of IsK activity.

Adenosine Triphosphate↗
PubMed1992

Cloning, functional expression, and regulation of two K+ channels in human T lymphocytes.

Low stringency screening of a Jurkat cDNA library with a rat brain K+ channel (RCK1) probe has resulted in the isolation of HLK3, a voltage-gated K+ channel. In Xenopus oocytes, the HLK3 clone directs the expression of a rapidly activating transient outward K+ current similar to the type n K+ current recorded in Jurkat T cells. The HLK3 gene is located on the short arm of human chromosome 1 (p13.3). Polymerase chain reaction was used to clone HIsK from Jurkat cDNA. The HIsK clone shares the same sequence with a previously described genomic clone (Murai, T., Kazikuka, A., Takumi, T., Ohkubo, H., and Nakanishi, S. (1989) Biochem. Biophys. Res. Commun. 161, 176-181). In Xenopus oocytes, it encodes a slowly activating, noninactivating K+ channel which cannot be recorded in Jurkat cells by conventional patch-clamp techniques. Transcripts of both clones are present at a similar level before and after activation of purified human T lymphocytes and Jurkat cells, reflecting a constitutive expression of K+ channel messages. This finding is in good agreement with the electrophysiological results for type n K+ current density on the same cells. HLK3 current is very sensitive to the scorpion toxin charybdotoxin (IC50 = 0.8 nM). HIsK current is totally insensitive to this toxin but is blocked by the antiarrhythmic clofilium (IC50 = 80 microM). While charybdotoxin has no effect on interleukin 2 mRNA induction, clofilium potently inhibits interleukin 2 mRNA expression upon mitogen-induced T cell activation. It is concluded that the HLK3 channel is not an important component of the T cell mitogenic response. Other targets for K+ channel blockers, such as the HIsK protein, could be involved in the activation process.

Amino Acid Sequence↗
PubMed1992

ISK, a slowly activating voltage-sensitive K+ channel. Characterization of multiple cDNAs and gene organization in the mouse.

mISK is a protein consisting of 129 amino acids with a single putative transmembrane domain. The injection of mISK cRNA into Xenopus oocytes directs the expression of a voltage-gated K+ current. A heart mRNA blot probed with mISK DNA revealed at least two transcripts. The messenger diversity of mISK was investigated by cloning and characterization of multiple cDNAs of one genomic clone, and by performing primer extension experiments. All cDNAs characterized have the same protein-coding sequence, and heterogeneity of the transcripts arises from alternative splicing, and multiple sites of transcription start and polyadenylation. ISK is encoded by a single gene in the mouse genome. The gene organization reveals the existence of an exon containing the whole protein-coding sequence and of two alternative exons corresponding to the 5' untranslated sequences. We failed to detect the presence of another exon capable of extending the protein-coding sequence. The diversity of mISK messengers is not associated with a diversity of the mISK protein.

Amino Acid Sequence↗
PubMed1992

Activation and inhibition of ATP-sensitive K+ channels by fluorescein derivatives.

Fluorescein derivatives are known to bind to nucleotide-binding sites on transport ATPases. In this study, they have been used as ligands to nucleotide-binding sites on ATP-sensitive K+ channels in insulinoma cells. Their effect on channel activity has been studied using 86Rb+ efflux and patch-clamp techniques. Fluorescein derivatives have two opposite effects. First, like ATP, they can inhibit active ATP-sensitive K+ channels. Second, they are able to reactivate ATP-sensitive K+ channels subjected to inactivation or "run-down" in the absence of cytoplasmic ATP. Therefore reactivation of the inactivated ATP-sensitive K+ channel clearly does not require channel phosphorylation as is commonly believed. The results indicate the existence of two binding sites for nucleotides, one activator site and one inhibitor site. Irreversible binding at either the inhibitor or the activator site on the channel was obtained with eosin-5-maleimide, resulting in irreversible inhibition or activation of the ATP-sensitive K+ channel respectively. The irreversibly activated channel could still be inhibited by 2 mM ATP. After activation by fluorescein derivatives, ATP-sensitive K+ channels become resistant to the classical blocker of this channel, the sulfonylurea glibenclamide. Negative allosteric interactions between fluorescein/nucleotide receptors and sulfonylurea-binding sites were suggested by results obtained in [3H]glibenclamide-binding experiments.

Adenosine Triphosphate↗
PubMed1992

Scyllatoxin, a blocker of Ca(2+)-activated K+ channels: structure-function relationships and brain localization of the binding sites.

Chemical modifications of scyllatoxin (leiurustoxin I) have shown that two arginines in the sequence, Arg6 and Arg13, are essential both for binding to the Ca(2+)-activated K+ channel protein and for the functional effect of the toxin. His31 is important both for the binding activity of the toxin and for the induction of contractions on taenia coli. However, although its iodination drastically decreases the toxin activity, it does not abolish it. Chemical modification of lysine residues or of Glu27 does not significantly alter toxin binding, but it drastically decreases potency with respect to contraction of taenia coli. The same observation has been made after chemical modification of the lysine residues. The brain distribution of scyllatoxin binding sites has been analyzed by quantitative autoradiographic analysis. It indicates that apamin (a bee venom toxin) binding sites are colocalized with scyllatoxin binding sites. The results are consonant with the presence of apamin/scyllatoxin binding sites associated with Ca(2+)-activated K+ channels. High-affinity binding sites for apamin can be associated with very-high-affinity (less than 70 pM), high-affinity (approximately 100-500 pM), or moderate-affinity (greater than 800 pM) binding sites for scyllatoxin.

Amino Acid Sequence↗