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M Lazdunski

Publications and source records attributed to M Lazdunski.

At least 181 records · Page 10Linked to original sources
PubMed1994

CGRP-induced activation of KATP channels in follicular Xenopus oocytes.

The two-microelectrode voltage-clamp technique was used to monitor K+ channel activity in Xenopus oocyte follicular cells, which are electrically coupled to the oocyte itself by gap junctions. Endogenous vasodilators such as calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP), prostaglandin E2 (PGE2) and adenosine activate glibenclamide-ATP-sensitive K+ (KATP) channels in Xenopus oocyte follicular cells. The mechanism of action of CGRP was studied in detail. CGRP effects undergo a rapid desensitization. CGRP acts via CGRPI receptors. Its effects are antagonised by the amino-truncated CGRP analog hCGRP(8-37). The second messenger for CGRP activation of KATP channels is cAMP. Phosphodiesterase inhibition by 3-isobutyl-1-methylxanthine enhances the CGRP response while adenyl cyclase inhibition by either 2',5'-dideoxyadenosine or progesterone nearly completely depresses the CGRP response. Vasoconstrictors such as ACh and angiotensin II also have receptors in follicular cells. ACh strongly inhibits the CGRP activation of K+ channels as it inhibits the activation of KATP channels by P1060, but angiotensin II does not. It is concluded that as in vascular smooth muscle cells, CGRP and probably other hyperpolarizing vasodilators open KATP channels in follicular cells by protein kinase A activation.

1-Methyl-3-isobutylxanthine↗
PubMed1994

Identification of the Ca2+ current activated by vasoconstrictors in vascular smooth muscle cells.

The noncontractile aortic cell line A7r5 was chosen to study the effect of the vasoconstrictor peptide vasopressin on transmembrane Ca2+ movements, using conventional whole-cell patch recording techniques. Conditions in which previously characterised vasoconstrictor-modulated currents were suppressed revealed a tiny inward current component (-18 +/- 2 pA, n = 50, at -61 mV in 110 mM CaCl2). The vasopressin-activated inward current was absent when Ca2+ was absent from the extracellular solution, and the current amplitude increased with [Ca2+] (0.01-110 mM), with an apparent dissociation constant for Ca2+ of 9.7 mM. It was highly selective for Ca2+ over monovalent cations (permeability ratio Ca/Cs greater than 17). It was not voltage gated, except that the current/potential characteristic showed some inwards rectification. Amplitudes of the evoked inward currents had the same order of magnitude in Sr2+ and Ca2+, whereas they were much smaller in Mn2+, suggesting that this pathway is highly permeable to Sr2+ but poorly permeable to Mn2+. Inward currents evoked in Ca2+ were inhibited by other cations with the following order of potency: La3+ > Cd2+ > Co2+ approximately Ni2+ approximately Mn2+. The channel producing this current corresponds most probably to the ionic pathway originally called the receptor-operated calcium channel, which produces a long-lasting, constrictor-induced plateau of increased intracellular free calcium concentration in smooth muscle.

Animals↗
PubMed1994

ATP-sensitive potassium channels: an overview.

ATP-sensitive potassium channels are found in a number of different tissues where they undertake distinct physiologic functions. In endocrine cells they regulate the secretion of hormones such as insulin, prolactin, and growth hormone. They influence the excitability of cardiac, skeletal, and vascular smooth muscle. They are of particular importance during ischemia in both the heart and the brain, where they intervene to reduce or delay cell death. Both electrophysiologic and pharmacologic evidence points toward ATP-sensitive potassium channels making up a class of ion channels with tissue-specific as well as functional differences. There is therefore considerable scope for the development of specific products to either enhance or inhibit the action of these ion channels under different pathologic conditions.

Adenosine Triphosphate↗
PubMed1994

Effects of a new class of calcium antagonists, SR33557 (fantofarone) and SR33805, on neuronal voltage-activated Ca++ channels.

SR33557 (fantofarone) and SR33805 are structurally novel calcium antagonists that bind selectively to the alpha 1-subunit of the L-type Ca++ channel at a site distinct from the classical 1,4-dihydrophyridine, phenylalkylamine and benzothiazepine sites but in allosteric interactions with them. Blocking effects of fantofarone and SR33805 on the different types of voltage-activated Ca++ currents have been investigated with the whole-cell patch-clamp method in chick dorsal root ganglion neurons (for T-, L- and N-type currents) and in rat cerebellar Purkinje neurons (for P-type current) in primary culture. Neuronal L-type Ca++ channels are blocked totally by fantofarone and SR33805 in the microM range of concentration as in skeletal muscle and cardiac cells at a holding membrane potential of -80 mV. The sequence of efficacy is SR33805 (IC50 = 26 nM) > fantofarone (IC50 = 0.35 microM). N- and P-type channels are not very sensitive to fanto-farone and SR33805 (IC50 approximately 5 microM). The T-type channel is not affected by these drugs.

Animals↗
PubMed1994

Functional receptors in Xenopus oocytes for U-37883A, a novel ATP-sensitive K+ channel blocker: comparison with rat insulinoma cells.

Follicle-enclosed Xenopus oocytes were used to describe the ATP-sensitive K+ (KATP) channel-blocking properties of U-37883A (4-morpholinecarboximidine-N-1-adamantyl-N'-cyclohexyl), in comparison with glibenclamide. In follicular oocytes, the KATP channel opener P1060 (30 microM), a pinacidil analog, activated a large outward K+ current that was blocked by glibenclamide (IC50 = 0.33 microM) and U-37883A (IC50 = 0.26 microM). P1060 activation was inhibited by both U-37883A and glibenclamide in a noncompetitive manner. U-37883A also blocked the KATP channel activation by cAMP (300 microM) and adenosine (10 microM). Single-channel studies on isolated follicular cells showed that U-37883A (10 microM) reduced the open probability of the KATP channel by 76%, without significantly modifying the single-channel current amplitude. Receptor binding studies with [3H]U-37883 in membranes from follicle-enclosed oocytes demonstrated a single class of low affinity binding sites, with a Kd of 450 nM and a Bmax of 17 pmol/mg of protein. Studies with analogs of U-37883A showed that U-52090A inhibited KATP current and displaced [3H]U-37883 from its binding site with similar potencies. In contrast, U-42069D neither inhibited KATP current nor competed with [3H]U-37883 binding. In RINm5F cells (an insulinoma cell line), U-37883A, unlike glibenclamide, failed to inhibit KATP current. Furthermore, there was no significant specific binding of [3H]U-37883 in RINm5F cell membranes, which displayed high levels of specific binding of [3H]glibenclamide. These data demonstrate the presence of a receptor for U-37883A-type guanidines that controls the activity of the endogenous KATP channels in follicle-enclosed oocytes. The available data collectively suggest that U-37883A is a more selective blocker of the follicular KATP channel, which is very similar to that in smooth muscle, than of the pancreatic beta cell KATP channel.

Adamantane↗
PubMed1993

Multiple mRNA isoforms encoding the mouse cardiac Kv1-5 delayed rectifier K+ channel.

The mouse Kv1-5 K+ channel cDNA has been cloned from heart. This channel was highly expressed in heart and, to a lesser extent, in other tissues, including brain and thymus. Two alternatively spliced isoforms were found. The longer form encoded a 602-amino acid protein, while in the short form (Kv1-5 delta 5'), the first 200 amino acids lying upstream the transmembrane segment S1 were deleted. RNase protection experiments showed that both Kv1-5 mRNA isoforms are present in the mouse tissues examined, the longer form being predominant. The short mRNA (Kv1-5 delta 5') arose by an unusual splicing event within the exonic sequence. An additional short cDNA clone (Kv1-5 delta 3') that codes for a carboxyl-terminal truncated protein has been isolated. The gene coding sequence contained a single exon and has been mapped on human chromosome 12 (p13) and on mouse chromosome 6 (band F). Expression in Xenopus oocytes revealed that the long (Kv1-5) and the amino-terminal deleted (Kv1-5 delta 5') isoforms elicited similar K+ currents with a drastically decreased efficacy for Kv1-5 delta 5'. The carboxyl-terminal truncated Kv1-5 delta 3' clone was not functional but inhibited the expression of the long isoform.

Alternative Splicing↗
PubMed1993

The protein IsK is a dual activator of K+ and Cl- channels.

The protein IsK (M(r) 14,500) is present in epithelial cells, heart, uterus and lymphocytes and induces slowly activating K+ currents when expressed in Xenopus oocytes. The finding that mutations of its single transmembrane segment altered channel gating or selectivity has suggested that IsK is a channel-forming protein. But IsK does not exhibit the K+ channel hallmarks (a conserved K+ selective pore (H5) flanked by either six or two membrane-spanning regions). Here we report that IsK expression in Xenopus oocytes also induces a Cl- selective current very similar to the Cl- current produced by phospholemman expression and with biophysical, pharmacological and regulation characteristics very different from those of the IsK-induced K+ channel activity. IsK mutagenesis identifies amino- and carboxy-terminal domains as critical for the induction of Cl- and K+ channel activities, respectively. Our data lead to a model in which the IsK protein (now called IsK, Cl) acts as a potent activator of endogenous and otherwise silent K+ or Cl- channels.

Amino Acid Sequence↗
PubMed1993

K+ channel openers prevent global ischemia-induced expression of c-fos, c-jun, heat shock protein, and amyloid beta-protein precursor genes and neuronal death in rat hippocampus.

Transient global forebrain ischemia induces in rat brain a large increase of expression of the immediate early genes c-fos and c-jun and of the mRNAs for the 70-kDa heat-shock protein and for the form of the amyloid beta-protein precursor including the Kunitz-type protease-inhibitor domain. At 24 hr after ischemia, this increased expression is particularly observed in regions that are vulnerable to the deleterious effects of ischemia, such as pyramidal cells of the CA1 field in the hippocampus. In an attempt to find conditions which prevent the deleterious effects of ischemia, representatives of three different classes of K+ channel openers, (-)-cromakalim, nicorandil, and pinacidil, were administered both before ischemia and during the reperfusion period. This treatment totally blocked the ischemia-induced expression of the different genes. In addition it markedly protected neuronal cells against degeneration. The mechanism of the neuroprotective effects involves the opening of ATP-sensitive K+ channels since glipizide, a specific blocker of that type of channel, abolished the beneficial effects of K+ channel openers. The various classes of K+ channel openers seem to deserve attention as potential drugs for cerebral ischemia.

Alternative Splicing↗
PubMed1993

Molecular cloning and functional expression of different molecular forms of rat amiloride-binding proteins.

The colon and lung amiloride-binding proteins were cloned from rat tissues. Two sizes of transcripts were identified. The 2.7-kb transcript codes for an 85-kDa protein, whereas the 1.2-kb transcript codes for a 25-kDa polypeptide. The 2.7-kb transcript was detected in the proximal and distal colon and in duodenum, liver, placenta and thymus. The 1.2-kb transcript was the only form present in lung and spleen, and it was also detected in placenta and colon. The short form corresponds to the 3' terminus of the longer one. It is formed by alternative transcription under the control of an internal promoter. Cells stably transfected with cDNAs encoding these two proteins were used for binding studies using [3H]phenamil, a potent blocker of the epithelial Na+ channel, derived from amiloride. Both the long and short forms of the protein bind amiloride and some of its derivatives, but they have distinct pharmacologies. The order of potency of the different amiloride derivatives to inhibit [3H]phenamil binding was phenamil (K0.5 = 10 nM) > benzamil (K0.5 = 43 nM) > amiloride (K0.5 = 1.4 microM) approximately ethylisopropylamiloride (K0.5 = 1.6 microM) for the long form, whereas it was phenamil (K0.5 = 68 nM) > amiloride (K0.5 = 3.2 microM) approximately ethylisopropylamiloride (K0.5 = 4 microM) approximately benzamil (K0.5 = 6.3 microM) for the short form. Although the binding proteins described here are distinct from the pore-forming protein of the epithelial Na+ channel, the pharmacological profile of the long form of the ABP is identical to that described previously in pig and human kidney, and similar to that expected for an epithelial Na+ channel. The pharmacological profile of the short form resembles that previously described for an amiloride-binding protein in pneumocytes. Results presented in this paper suggest that previously purified preparations showing Na+ channel activity contain different forms of the amiloride-binding protein, possibly associated with other proteins. The similarity between amiloride-binding proteins and a protein identified in seminal vesicles suggests that amiloride-binding proteins are the first members of a new family of epithelia-specific proteins.

Amine Oxidase (Copper-Containing)↗
PubMed1993

Pharmacological properties of ATP-sensitive K+ channels in mammalian skeletal muscle cells.

The patch-clamp technique (single-channel recordings) was used to study the effects of glibenclamide and some channel openers on the KATP channel in mouse skeletal muscle. In outside/out membrane patches, glibenclamide reversibly inhibited KATP channel activity in a dose-dependent manner with an apparent Ki of 190 nM. In inside/out membrane patches, RP 61419 increased KATP channel activity both in the absence and in the presence of internal ATP while other K+ channel openers such as nicorandil and cromakalim required the presence of internal ATP to evoke channel activation. The half-maximal activity effect for cromakalim, with 0.5 mM ATP at the cytoplasmic face, was observed at about 220 microM. Pinacidil was unable to activate the KATP channel in the absence of internal ATP and could even reduce channel opening in situations where activity was high in the control. In the presence of internal Mg2+, activation by pinacidil occurred when ATP or low and weakly activating concentrations of ADP were present at the cytoplasmic side. Pinacidil activation could also be observed in the presence of ATP or ADP when Mg2+ was absent from the internal solution. The mechanism of action of pinacidil is discussed in terms of interactions between the different nucleotide regulatory sites and the K+ channel opener binding site of the KATP channel. Half-maximum activation of the KATP channel in the presence of 0.5 mM ATP at the cytoplasmic face was observed at 125 microM pinacidil.

Adenosine Triphosphate↗
PubMed1993

Expression cloning of an epithelial amiloride-sensitive Na+ channel. A new channel type with homologies to Caenorhabditis elegans degenerins.

A complementary DNA encoding an amiloride-sensitive Na+ channel has been cloned and characterized from rat colon. The protein encoded by the cDNA has a sequence of 699 amino acids (79 kDa) containing several putative membrane spanning domains and potential phosphorylation sites. It forms a channel that has the electrophysiological and pharmacological properties characteristic of the epithelial Na+ channel. Homologies (including in transmembrane domains) have been found between a part of the channel sequence and the Mec4 gene product of Caenorhabditis elegans, a protein associated with mutation-induced neuronal degeneration.

Amiloride↗
PubMed1993

ATP-modulated K+ channels sensitive to antidiabetic sulfonylureas are present in adenohypophysis and are involved in growth hormone release.

The adenohypophysis contains high-affinity binding sites for antidiabetic sulfonylureas that are specific blockers of ATP-sensitive K+ channels. The binding protein has a M(r) of 145,000 +/- 5000. The presence of ATP-sensitive K+ channels (26 pS) has been demonstrated by electrophysiological techniques. Intracellular perfusion of adenohypophysis cells with an ATP-free medium to activate ATP-sensitive K+ channels induces a large hyperpolarization (approximately 30 mV) that is antagonized by antidiabetic sulfonylureas. Diazoxide opens ATP-sensitive K+ channels in adenohypophysis cells as it does in pancreatic beta cells and also induces a hyperpolarization (approximately 30 mV) that is also suppressed by antidiabetic sulfonylureas. As in pancreatic beta cells, glucose and antidiabetic sulfonylureas depolarize the adenohypophysis cells and thereby indirectly increase Ca2+ influx through L-type Ca2+ channels. The K+ channel opener diazoxide has an opposite effect. Opening ATP-sensitive K+ channels inhibits growth hormone secretion and this inhibition is eliminated by antidiabetic sulfonylureas.

Adenosine Diphosphate↗
PubMed1993

Endothelin and vasopressin activate low conductance chloride channels in aortic smooth muscle cells.

The non-contractile aortic smooth muscle cell line A7r5 was used to study the membrane events involved in the effect of vasoconstrictor peptides. Whole-cell voltage-clamp and membrane potential recording techniques were used to demonstrate the contribution of an increased Cl- conductance to the late depolarization induced by endothelin-1 and vasopressin. During cell-attached patch recording with N-methyl-D-glucamine in the pipette, bath application of endothelin or vasopressin induced single-channel inward currents in the following minutes. The current/potential (I/V) curve of the most frequently observed channel type--a small conductance Cl- (SCl) channel--reversed near the cell membrane potential and showed a single-channel conductance of 1.8 pS for inward currents. After patch excision in an extracellular solution containing CaCl2 (2 mM), the frequency of SCl channel openings increased. Patch excision in the absence of peptide stimulation also produced this channel activity. Replacement of CaCl2 by a Ca2+ chelator on the intracellular face of a patch reversibly inhibited the channel activity, indicating that these SCl channels are Ca(2+)-activated Cl- channels. The single-channel I/V characteristic showed outward rectification above +50 mV. An analysis of the gating kinetics of the SCl channel is given. Another channel type was recorded less frequently after peptide stimulation. It had a lower conductance (1.0-1.3 pS) and slower kinetics and was designated a very small conductance Cl- channel. It is concluded that activation of two types of Cl- channels (at least one of which is Ca2+ dependent) is involved in the late depolarization produced by vasoconstrictor peptides in vascular smooth muscle cells of the aortic cell line A7r5.

Adenosine Triphosphate↗
PubMed1993

Single-channel properties and regulation of pinacidil/glibenclamide-sensitive K+ channels in follicular cells from Xenopus oocyte.

Follicular oocytes from Xenopus laevis contain K+ channels that are activated by members of the recently recognized class of vasorelaxants that includes the pinacidil derivative P1060. These channels are blocked by antidiabetic sulphonylureas such as glibenclamide. Opening of the glibenclamide-sensitive K+ channels with P1060 promotes follicular oocyte maturation. Whole-cell and single-channel patch-clamp configurations were used to monitor K+ channel activity in isolated follicular cells. In the presence of micromolar concentrations of intracellular Mg2+ATP, P1060 activated a whole-cell K+ current that was blocked by glibenclamide. The P1060 response was depressed by millimolar concentrations of intracellular ATP and ATP[gamma S]. Single-channel recordings identified two different types of K+ channel. These channels differed in their unitary conductances (19 pS and 150 pS), in their sensitivities to internal Ca2+, to charybdotoxin and to pinacidil and glibenclamide. Only the Ca(2+)-independent K+ channel (19 pS) was activated by the pinacidil derivative and blocked by glibenclamide. Opening of the 19-pS glibenclamide-sensitive K+ channel by P1060 critically required the presence of a low concentration of Mg2+ATP in the intracellular medium. The 19-pS K+ channel was opened by increasing intracellular cAMP. Similar effects were obtained by intracellular application of the catalytic subunit of protein kinase A in the presence of micromolar concentrations of Mg2+ATP. Both acetylcholine and the phorbol ester phorbol 12-myristate 13-acetate blocked the 19-pS K+ channel after it was activated by P1060.

Acetylcholine↗
PubMed1993

Memory processing and apamin induce immediate early gene expression in mouse brain.

The present study analyses the effects of learning on the spatial pattern and the time-course of changes of immediate early gene messenger RNA's (c-fos and c-jun) in mouse brain produced by training in an appetitive bar-pressing task. Activation of c-fos and c-jun after training is strictly located in the hippocampal formation and is learning-dependent. Levels of both proto-oncogene mRNAs in the trained group were 4 to 5 times higher than in the sham-conditioned group. Injections of apamin, a bee venom neurotoxin that selectively blocks a class of Ca(2+)-activated K+ channels and improves learning and memory retention, produced as compared to untrained animals a 3- to 5-fold increase of expression of c-fos and c-jun with the same pattern as that observed in the trained animals. Post-training injection of 0.2 mg/kg apamin enhanced 1.4-fold the expression of both immediate early genes in CA1, CA3 and dentate gyrus as compared to trained saline-injected mice. All these results suggest that apamin-induced increase of immediate early gene expression might be related to the apamin-induced facilitation of learning.

Animals↗
PubMed1993

Are Xenopus oocytes unique in displaying functional IsK channel heterologous expression?

IsK is a novel membrane protein that induces a slow voltage-gated K+ current when expressed in Xenopus oocytes. Attempts were made to express this channel in several eukaryotic cells including the skeletal muscle cell line C2C12, the fibroblastic cell line CHO and the T lymphocyte cell line Jurkat. In spite of the clear demonstration of successful transfection, no IsK current could be recorded from these cells. Overexpression was also obtained using the vaccinia/T7 and baculovirus systems, again without any success in demonstrating the presence of the K+ current in the plasma membrane of infected cells. Bilayer reconstitution experiments using membranes highly enriched in IsK protein ruled out the possibility that the IsK protein could induce a K+ channel located in intracellular organelles. Collectively, these data suggest the possibility that IsK protein is part of a K+ channel complex but is only active in association with another protein endogenous to the Xenopus oocyte. Other hypotheses are also discussed.

Animals↗
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↗