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Biomedical subjects

M Lazdunski

Publications and source records attributed to M Lazdunski.

At least 271 records · Page 15Linked to original sources
PubMed1989

The inotropic effect of endothelin-1 on rat atria involves hydrolysis of phosphatidylinositol.

Endothelin-1 induces a positive inotropic response in isolated left atria of the rat with an IC50 value of 20 nM. The contractile effect of endothelin is larger than that of other inotropic hormones such as phenylephrine and epinephrine and smaller than that of Bay K8644. In the spontaneously active right atria, endothelin induces a positive inotropic effect with no chronotropic effect. Endothelin does not modify intracellular levels of cAMP under basal conditions or after stimulation with isoproterenol but stimulates the formation of inositol phosphates. Mobilization of inositol phospholipids is observed in the same range of concentrations as for the contractile action of endothelin. The contractile action of endothelin is not mediated by protein kinase C. It is antagonized by blockers of L-type Ca2+ channels, low external Ca2+ concentrations and drugs such as caffeine and ryanodine that interfere with Ca2+ release by the sarcoplasmic reticulum.

Animals↗
PubMed1989

A new type of amiloride-sensitive cationic channel in endothelial cells of brain microvessels.

Endothelial cells from brain microvessels form the blood-brain barrier. Brain microvessels and endothelial cells isolated from rat brain microvessels express an amiloride-sensitive cationic channel that was characterized using [3H]phenamil binding and patch-clamp experiments. [3H]Phenamil, a labeled amiloride analog, recognizes a single family of binding sites with a dissociation constant of 20-30 nM and a maximum binding capacity of 8-15 pmol/mg protein. The pharmacological profile of the channel (phenamil greater than benzamil greater than amiloride) is very similar to that of the epithelium Na+ channel of mammalian kidney and of frog epithelia. Long-lasting currents were observed in patch-clamp experiments using excised outside-out patches. Application of amiloride or phenamil first produced a rapid flickering of channel activity and then its complete blockade. The mean unit channel conductance at 140 mM Na+ was 23 picosiemens. The selectivity of Na+ over K+ was estimated from reversal potentials to be 1.5:1. Properties of the channel in microvessels are clearly distinct from those of the Na+ channel of the kidney, suggesting the existence of several isoforms of cationic channels that are sensitive to amiloride and its derivatives. The low selectivity cationic channel of endothelial cells in brain microvessels might be important for controlling both Na+ and K+ movements across the blood-brain barrier.

Amiloride↗
PubMed1989

Biochemical identification of two types of phenamil binding sites associated with amiloride-sensitive Na+ channels.

The existence of distinct forms of the epithelium Na+ channel that differ in their sensitivity to amiloride has been repeatedly suggested by physiological data. The biochemical basis for these differences was analyzed by using phenamil, the most potent inhibitor known so far for the epithelium Na+ channel. [3H]Phenamil of high radioactive specific activity (30 Ci/mmol) was prepared and used to titrate [3H]phenamil binding sites in pig kidney membranes. Kinetic experiments, equilibrium binding studies, and competition experiments indicated the presence in crude membrane preparations of two classes of independent binding sites. A first binding site was characterized by a high affinity for phenamil (Kd1 = 0.4 nM) and for amiloride (Kd1 = 0.1 microM). A second binding site recognized phenamil and amiloride with lower affinities [Kd2(phenamil) = 28 nM, Kd2(amiloride) = 4 microM]. The ratio of the respective amounts of low- and high-affinity binding sites was 14 +/- 2 in different membrane preparations (range: 6-22). The two types of binding sites for [3H]phenamil copurified and were still observed after purification of the epithelium Na+ channel to homogeneity. These results indicate that at least two types of pharmacologically distinguishable Na+ channels exist in the kidney. They correspond either to two isoforms of the apical Na+ channel or to one single type of channel under two different states of covalent regulation.

Amiloride↗
PubMed1989

Antidiabetic sulfonylureas: localization of binding sites in the brain and effects on the hyperpolarization induced by anoxia in hippocampal slices.

The distribution of antidiabetic sulfonylurea [( 3H]glibenclamide) binding sites is heterogeneous in rat brain. Pyramidal and extrapyramidal motor system contain the highest densities of sites, particularly in the substantia nigra and in the globus pallidus. Only low levels are present in the hypothalamic nuclei and the main medulla oblongata regions. In hippocampal formation the stratum lucidum and the stratum lacunosum moleculare of CA3 show an important density of glibenclamide binding sites. Electrophysiological studies with hippocampal slices show that glibenclamide blocks hyperpolarization induced by anoxia, suggesting the involvement of adenosine triphosphate-sensitive K+ channel in this early hyperpolarization event.

Action Potentials↗
PubMed1989

Guanabenz, guanochlor, guanoxan and idazoxan bind with high affinity to non-adrenergic sites in pig kidney membranes.

[3H]Idazoxan is a labelled ligand that is frequently used to study alpha 2-adrenoceptors in the central nervous system. In pig kidney membranes, [3H]idazoxan labelled high-affinity binding sites (Kd = 1.5 nM) that were not alpha 2-adrenoceptors and which recognized clonidine with low affinity. This new class of binding sites was recognized by amiloride derivatives; however, it is not likely that these sites are the well-known targets of amiloride in the kidney: the Na+/H+ exchanger and the epithelium Na+ channel. These binding sites may be the normal target of a series of imidazolidines derivatives (guanabenz, guanochlor, guanoxan), which are known for their antihypertensive properties.

Amiloride↗
PubMed1989

Ca2+ channel blockers prevent seizures induced by a class of K+ channel inhibitors.

Intracerebroventricular injection into rats of mast-cell degranulating peptide (MCD), dendrotoxin I (DTXI) and 4-aminopyridine (4-AP), three blockers of a subclass of K+ channels, elicited epileptiform wave bursts and convulsions. Three different types of L-type Ca2+ channel inhibitors (+)PN 200-110, a 1,4-dihydropyridine, (-)D888, a phenylalkylamine, and fluspirilene, a diphenylbutylpiperidine, were potent blockers of the convulsant-induced hyperexcitatory effects when they were administered preventively. D-AP5, a N-methyl-D-aspartate antagonist, was active on the 4-AP-induced seizures but was without effect on the MCD- and dendrotoxin-induced seizures.

4-Aminopyridine↗
PubMed1989

Diversity and novel pharmacological properties of Ca2+ channels in Drosophila brain membranes.

Binding studies as well as affinity labelling and immunoblot techniques were used to identify and characterize the receptors for Ca2+ channel blockers in Drosophila brain membranes. Despite structural analogies with mammalian receptors, Drosophila binding sites for phenylalkylamines and 1,4-dihydropyridines, unlike those described in skeletal and cardiac muscle, were found to be located on separate Ca2+ channels. Single-channel bilayer recordings from reconstituted membranes revealed the presence of eight distinct cobalt-sensitive Ba2+-conducting channels in Drosophila brain membrane preparations. In good agreement with binding studies, the most frequently observed Ca2+ channel type (Ba2+ conductance of 13 pS) was extremely sensitive to phenylalkylamines but not affected by micromolar concentrations of 1,4-dihydropyridines. Distinct 1,4-dihydropyridine-sensitive and phenylalkylamine-insensitive channels were also identified. They had unitary Ba2+ conductances of 21 and 31 pS. A detailed analysis of drug action showed that both 1,4-dihydropyridines and phenylalkylamines first increased channel open state probability before fully blocking channel activity. Other types of channels have been identified with unitary Ba2+ conductances of 9, 41, 53, 64 and 81 pS. They were insensitive to the previously described organic Ca2+ channel blockers. The Drosophila system seems to be a unique model to analyse the properties of several different types of Ca2+ channels and particularly those of channel types that are uniquely blocked by phenylalkylamines or uniquely blocked by 1,4-dihydropyridines.

Animals↗
PubMed1989

Ontogenesis and localization of Ca2+ channels in mammalian skeletal muscle in culture and role in excitation-contraction coupling.

The mechanism of excitation-contraction (E-C) coupling in skeletal muscle is not yet well established. Cultured mouse skeletal muscle cells have been used to study the relationships between triad formation, Ca2+ channel activities, and contractions. The ontogenesis of voltage-dependent Ca2+ channels and their localization in relation to the ability of muscle to contract and the ultrastructural organization of sarcomeres and triads have been investigated by using an electrophysiological approach together with an electron microscope study. At an early stage of development, both fast (Ifast) and slow (Islow) types of Ca2+ channels are found at the surface membrane. At later stages of development, fast Ca2+ channels remain at the surface membrane, while slow Ca2+ channels migrate to the transverse-tubule membrane. The voltage dependence of fast Ca2+ channels compared to the voltage dependence of contraction clearly shows that these Ca2+ channels have no direct role in E-C coupling. Detubulation at all stages of development has confirmed that T tubules contain essential elements for E-C coupling. However, this work also shows that Ca2+ flowing through slow Ca2+ channels situated in the T-tubular system is not important for contraction. Myotubes lacking slow Ca2+ channels or having no slow Ca2+ channel transport activity (jumps to high membrane potentials, no external Ca2+, block of Islow by Co2+) still retain contraction.

Animals↗
PubMed1989

Regulation of ATP-sensitive K+ channels in insulinoma cells: activation by somatostatin and protein kinase C and the role of cAMP.

The actions of somatostatin and of the phorbol ester 4 beta-phorbol 12-myristate 13-acetate (PMA) were studied in rat insulinoma (RINm5F) cells by electrophysiological and 86Rb+ flux techniques. Both PMA and somatostatin hyperpolarize insulinoma cells by activating ATP-sensitive K+ channels. The presence of intracellular GTP is required for the somatostatin effects. PMA- and somatostatin-induced hyperpolarization and channel activity are inhibited by the sulfonylurea glibenclamide. Glibenclamide-sensitive 86Rb+ efflux from insulinoma cells is stimulated by somatostatin in a dose-dependent manner (half maximal effect at 0.7 nM) and abolished by pertussis toxin pretreatment. Mutual roles of a GTP-binding protein, of protein kinase C, and of cAMP in the regulation of ATP-sensitive K+ channels are discussed.

Adenoma, Islet Cell↗
PubMed1989

Molecular mechanism of endothelin-1 action on aortic cells.

The vasoconstricting action of endothelin-1 (ET-1) is partly mediated by voltage-dependent L-type Ca2+ channels. Activation of the Ca2+ channels is indirect. ET-1 action involves (i) the hydrolysis of phosphatidylinositol and the release of Ca2+ from internal stores and (ii) the opening of a nonselective cation channel in the plasma membrane. The resulting depolarization triggers the activity of L-type Ca2+ channels.

Animals↗
PubMed1989

SR33557, an indolizinsulfone blocker of Ca2+ channels: identification of receptor sites and analysis of its mode of action.

SR33557 belongs to a new class of molecules (indolizinsulfones) that act on the same receptor complex that has been characterized for other classical calcium channel effectors. The main binding properties of SR33557 to rabbit skeletal muscle are as follows. (i) Unlabeled SR33557 completely inhibits the specific binding of all classes of calcium channel antagonists such as dihydropyridines [(+)-[3H]PN200-110], phenylalkylamines ([3H] verapamil), benzothiazepines (d-(cis)-[3H]diltiazem), and diphenybutylpiperidines ([3H]fluspirilene). In all these cases inhibition of binding is of a noncompetitive nature. (ii) [3H]SR33557 binds with high affinity to T tubule membranes (KD = 0.08 nM) and the maximum binding capacity (Bmax = 78 pmol/mg of protein) is the same as that found for other classes of Ca2+ channel antagonists. Photoaffinity labeling confirms that [3H]SR33557 associates with the same protein of Mr 165,000 that binds the classical calcium channel inhibitors. 45Ca2+ uptake experiments performed with the rat aortic cell line A7r5, the insulin-secreting cell line RINm5F, and the pheochromocytoma cell line PC12 demonstrate that SR33557 fully inhibits the 1,4-dihydropyridine-sensitive 45Ca2+ uptake elicited by depolarization. A very good correlation was found between inhibition of 45Ca2+ uptake and of [3H]dopamine release in PC12 cells and between inhibition of 45Ca2+ uptake and of L-type Ca2+ current in A7r5 cells under whole-cell patch-clamp conditions.

Adrenal Gland Neoplasms↗
PubMed1988

Molecular mechanism of action of the vasoconstrictor peptide endothelin.

Endothelin, one of the most potent vasoconstrictor known, has been suggested to act as an endogenous agonist of L-type Ca2+ channels. In this paper we show that endothelin stimulates the metabolism of inositol phosphates and induces the mobilization of intracellular Ca2+ stores. The transient activation of Ca2+-sensitive K+ channel provokes an hyperpolarization of the membrane. It is followed by a sustained depolarization which is due to the opening of a non-specific cation channel which is permeable to Ca2+ and Mg2+. The depolarization then activates L-type Ca2+ channels. This mechanism of action explains why part of the endothelin-induced vasocontriction is eliminated by L-type Ca2+ channel blockers.

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