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M Wibo

Publications and source records attributed to M Wibo.

At least 19 recordsLinked to original sources
PubMed1994

Comparative localization of inositol 1,4,5-trisphosphate and ryanodine receptors in intestinal smooth muscle: an analytical subfractionation study.

[3H]Ins(1,4,5)P3- and [3H]ryanodine-binding sites were characterized in membrane fractions from guinea-pig intestinal smooth muscle (longitudinal layer) and their subcellular localization was investigated by analytical cell-fractionation techniques. Fractions collected at low centrifugal fields (N and M fractions) contained predominantly low-affinity [3H]Ins(1,4,5)P3-binding sites (KD 80 nM), whereas microsomal (P) fractions contained only high-affinity binding sites (KD 5 nM). Total sedimentable high-affinity binding sites of [3H]Ins(1,4,5)P3 were 9-10-fold more numerous than those of [3H]ryanodine. Both high-affinity binding sites were purified in microsomal fractions, and their sub-microsomal distribution patterns after isopycnic density-gradient centrifugation were similar to those of presumed endoplasmic reticulum (ER) constituents, indicating that Ins(1,4,5)P3 and ryanodine receptors were localized primarily in ER and probably associated with rough as well as smooth ER. However, the stoichiometric ratio of Ins(1,4,5)P3 to ryanodine receptors was distinctly higher in high-density RNA-rich subfractions than in low-density RNA-poor subfractions, suggesting that Ins(1,4,5)P3 receptors were somewhat concentrated in the ribosome-coated portions of ER. The low overall stoichiometric ratio of ryanodine to Ins(1,4,5)P3 receptors in intestinal smooth muscle (1:9-10) might explain, at least partly, the existence of a Ca(2+)-storage compartment devoid of ryanodine-sensitive Ca2+ channels, but equipped with Ins(1,4,5)P3-sensitive channels, in saponin-permeabilized smooth-muscle cells [Iino, Kobayashi and Endo (1988) Biochem. Biophys. Res. Commun. 152, 417-422].

Animals↗
PubMed1992

Interaction of pinaverium (a quaternary ammonium compound) with 1,4-dihydropyridine binding sites in rat ileum smooth muscle.

1. The interaction of pinaverium bromide, a quaternary ammonium compound, with binding sites for (L-type) calcium channel blockers was investigated in rat ileum smooth muscle. 2. Pinaverium inhibited [3H]-(+)-PN200-110 ([3H]-(+)-isradipine) specific binding to tissue homogenates incompletely (Ki 0.38 microM; maximal inhibition 80%). In contrast, binding to single cell preparations (obtained by collagenase treatment) and to saponin-treated homogenates was completely inhibited. These data are compatible with the view that, in untreated homogenates, 20% of [3H]-(+)-isradipine binding sites are not accessible to pinaverium because it is associated with sealed inside-out vesicles. 3. Pinaverium bromide increased the apparent KD of [3H]-(+)-isradipine binding to saponin-treated homogenates but did not significantly affect the Bmax value. Moreover, the dissociation rate constant of [3H]-(+)-isradipine binding was not changed by pinaverium. These data suggest that pinaverium interacts with the dihydropyridine binding site in a competitive manner. However, in contrast to uncharged dihydropyridine calcium antagonists, pinaverium inhibited, rather than stimulated, [3H]-diltiazem binding to rat brain membranes (at 30-37 degrees C). 4. Although Bmax values of [3H]-(+)-isradipine were similar in homogenates prepared from tissue and cells (collagenase-treated), the KD value was significantly higher in cell homogenates (166 vs 95 pM). Similarly, the Ki value of pinaverium was higher in cell preparations than in tissue homogenates (0.77 vs 0.38 microM). Thus, collagenase can significantly modify the dihydropyridine recognition site.5. The competitive interaction of pinaverium, a permanently charged drug, with [3H]-(+)-isradipine bound to intact cells and its absence of interaction with [3H]-(+)-isradipine bound to sealed inside-out vesicles imply that the dihydropyridine receptor lies near the external surface of the plasma membrane.

Animals↗
PubMed1991

Distribution of alpha 1 and alpha 2 (Na+,K+)-ATPase isoforms between the junctional (t-tubular) and non-junctional sarcolemmal domains of rat ventricle.

The alpha 1 and alpha 2 (Na+,K+)-ATPase isoforms in microsomal fractions from adult rat ventricle could not be separated by density gradient centrifugation. Both isoforms were mainly recovered in low-density subfractions and their distribution pattern was superimposable to those of other typical plasma membrane constituents (5'-nucleotidase, muscarinic receptors) but differed from that of 1,4-dihydropyridine receptors, which were mainly associated with high-density subfractions. Thus, both (Na+,K+)-ATPase isoforms were present essentially in the non-junctional sarcolemmal domain, i.e. at the cell surface, while 1,4-dihydropyridine receptors (voltage-dependent calcium channels) seemed much more concentrated in the junctional domain, which is predominantly of t-tubular origin. Therefore, the high inotropic efficacy of low ouabain concentrations in rat ventricle cannot be explained on the basis of a preferential localization of the high-affinity receptors (alpha 2 isoform) in the vicinity of junctional structures. The difference in inotropic efficacy between high and low ouabain concentrations might be related to differences in stimulus response coupling associated with alpha 1 and alpha 2 isoforms, as suggested by the greater sensitivity of the effect of low concentrations to ethylisopropylamiloride, an inhibitor of Na(+)-H+ exchange.

5'-Nucleotidase↗
PubMed1991

Binding sites for 1,4-dihydropyridine Ca(2+)-channel modulators in rat intestinal smooth muscle.

The contractile response of intestinal smooth muscle to depolarization is characterized by a phasic and a tonic component which are differently sensitive to blockade by 1,4-dihydropyridines. As this difference in sensitivity could be related to different binding sites associated with distinct calcium channels, we analyzed the binding of the calciumantagonist 1,4-dihydropyridine (+)PN 200-110 [isopropyl-4-(2,1,3-benzodiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5- methoxycarbonyl-pyridine-3-carboxylate] in longitudinal smooth muscle of the rat ileum. We carried out saturation binding experiments on intact tissue exposed to physiological and depolarizing (100 mmol l-1 K+) solution, and on different membrane fractions: the total microsomal fraction, the light microsomal fraction (enriched with plasma membranes) and the mitochondrial fraction. Binding of 3H(+)PN 200-110 to the intact longitudinal smooth muscle of rat ileum appeared to be voltage-dependent, KD decreased in depolarized tissue whereas Bmax was unchanged (change in membrane potential was assessed by measuring the distribution of 3H-tetraphenylphosphonium bromide). In membrane fractions two binding sites were detected, a high-affinity site associated with plasma membrane and a low-affinity site presumably associated with mitochondria (abundant in the fractions where the cytochrome c oxidase activity was high, and undetectable in the light microsomes poor in cytochrome c oxidase activity). The KD value of the high-affinity binding in isolated membrane fractions was similar to the KD value measured in intact depolarized tissue. The low affinity binding increased at high ionic strength and did not display any stereoselectivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Postnatal maturation of excitation-contraction coupling in rat ventricle in relation to the subcellular localization and surface density of 1,4-dihydropyridine and ryanodine receptors.

To better understand excitation-contraction coupling in cardiac muscle, we investigated the main Ca2+ channels involved in that process in adult and neonatal rat ventricle. Voltage-dependent (L-type) Ca2+ channels and sarcoplasmic reticulum Ca2+ release channels were labeled by means of [3H] (+)-PN200-110 and [3H]ryanodine, respectively. The number of [3H]ryanodine binding sites (per gram tissue) increased more than that of [3H] (+)-PN200-110 binding sites over the postnatal period (2.1-fold versus 1.35-fold, respectively). After equilibration of microsomal fractions in density gradient, ryanodine receptors were characterized by a heavy distribution pattern that did not change appreciably between days 1 and 30 after birth. In neonatal tissue, 1,4-dihydropyridine receptors were found mainly in low-density subfractions, together with other sarcolemmal constituents, whereas in adult tissue, they were recovered predominantly in high-density subfractions, together with ryanodine receptors. Thus, after birth, and in parallel with the development of T tubules, there was a progressive concentration of L-type Ca2+ channels in junctional structures of high equilibrium density, where they were situated close to the Ca2+ release channels of the sarcoplasmic reticulum. In adult ventricle, L-type channels were, on an average, threefold more abundant in T tubules than in external sarcolemma. In parallel mechanical studies, we found that the inhibitory action of ryanodine on systolic contraction was much more pronounced in adult than in neonatal right ventricle, and that, conversely, neonatal tissue was more sensitive that adult tissue to inhibitors of L-type channels. We conclude that, in view of the presumed mechanism of Ca2+ release from the sarcoplasmic reticulum, that is, Ca(2+)-induced Ca2+ release, the predominant localization in adult rat ventricle of the major Ca2+ entry pathway in the vicinity of the Ca2+ release pathway is of great functional significance. Furthermore, owing to the relative stoichiometry of Ca2+ entry and Ca2+ release channels in junctional structures (about 1:9), a physical link between these channels is not likely to be involved in the modulation of Ca2+ release from the sarcoplasmic reticulum in cardiac muscle.

Animals↗
PubMed1991

Effects of a chronic treatment by nisoldipine, a calcium antagonistic dihydropyridine, on arteries of spontaneously hypertensive rats.

Earlier studies have shown that relaxation in response to several agents is impaired in arteries from spontaneously hypertensive rats (SHR). We had previously reported that SHR aortas present a delayed relaxation when first exposed for 35 minutes to a 100 mM KCl solution and then transferred into physiological solution. The first phase of relaxation appeared similar in SHR and Wistar-Kyoto rat arteries, but the second phase was markedly slowed down in SHR arteries, giving rise to a postcontraction tone. In this study, we found that this postcontraction tone could be demonstrated not only in the aorta but also in the mesenteric artery, was independent of the presence of endothelium, increased with the age of SHR, and disappeared progressively when arterial segments were submitted to successive cycles of KCl depolarization followed by reimmersion in physiological solution. Chronic treatment of SHR with nisoldipine at doses that blocked the development of hypertension and attenuated the concomitant hypertrophy of heart and aorta, or in vitro pretreatment of SHR arteries with nisoldipine, decreased the contractile force developed by arteries in response to KCl depolarization and normalized the subsequent relaxation. [3H] (+)-PN200-110 binding studies on heart and brain homogenates indicated an increase in apparent Kd in nisoldipine-fed rats without significant change in Bmax. Binding data were compatible with the view that occupation of dihydropyridine receptors by nisoldipine after chronic oral administration was responsible for the modifications observed ex vivo in the mechanical activity of arteries. We conclude that the postcontraction tone of SHR arteries was mainly due to an abnormally prolonged activation of calcium channels after transfer of depolarized arteries into the physiological solution and that a labile or slowly releasable factor was probably involved in this phenomenon. We suggest that the antihypertensive action of nisoldipine might be related to the mechanisms involved in the suppression of the postcontraction tone as observed in vitro and that this mode of action could be more important than the vasodilating effect of this drug.

Animals↗
PubMed1990

Modulation of the action of calcium antagonists in arteries.

This paper is a review of the experimental evidence showing that specific binding sites for dihydropyridine Ca antagonists are involved in inhibition of stimulus-dependent Ca entry into arterial cells and thereby in inhibition of the contractile response. The apparent affinity of the dihydropyridine binding site is related to the proportion of a high- and a low-affinity state which is regulated by membrane potential but could also be dependent upon other factors such as G proteins. Among Ca antagonists, a subgroup of agents exhibiting voltage dependence may be identified. Their apparent pharmacological potency is highly dependent on resting membrane potential and on the duration of the depolarizing stimulus.

Animals↗
PubMed1990

[Postnatal maturation of excitation-contraction coupling of the heart].

We have studied the post-natal maturation of excitation-contraction coupling in rat ventricle by means of pharmacological agents that selectively modulate either Ca entry via voltage-dependent sarcolemmal channels (dihydropyridines) or Ca release from sarcoplasmic reticulum (ryanodine). We have investigated the effects of those agents on cardiac contractility, and we have used them as radioligands to examine the properties of their receptors. Our results show that, after birth, dihydropyridine receptors (i.e. voltage-dependent Ca channels) redistribute to transverse tubules, in close proximity of terminal cisternae of sarcoplasmic reticulum. This redistribution favors the mechanism whereby, in adult ventricle, extracellular Ca entry triggers Ca release from sarcoplasmic reticulum.

Animals↗
PubMed1989

Effect of endothelin-1 on calcium channel gating by agonists in vascular smooth muscle.

Rat isolated aorta was more sensitive to the contractile effect of endothelin-1 (ET-1) when the endothelium was removed. ET-1 was more potent on mesenteric resistance arteries than on aorta. A threshold concentration of ET-1 (100 pM) enhanced the contractile responses of aortic rings to Bay K 8644 and clonidine, especially in the absence of endothelium. Potentiation of clonidine-evoked contraction was accompanied by an enhancement of 45Ca influx and was abolished by nifedipine. These actions of ET-1 (100 pM) could not be attributed to a decrease in membrane potential or in cAMP levels. ET-1 (100 pM) decreased cGMP in intact aortic rings, which could contribute to its actions in the presence of endothelium. Removal of endothelium reduced cGMP levels and these were not further decreased by ET-1. Since ET-1 exerted a pronounced potentiating effect in the absence of endothelium, it is likely that ET-1 modulates calcium channels by an additional mechanism, unrelated to cyclic nucleotides.

Animals↗
PubMed1988

Pharmacologic relevance of dihydropyridine binding sites in membranes from rat aorta: kinetic and equilibrium studies.

The kinetic features of the interaction of dihydropyridines with rat aortic smooth muscle were investigated in parallel mechanical and binding studies. The inhibitory action of (+)-PN200-110 and nisoldipine on contractions evoked by potassium chloride depolarization was characterized by a pronounced time dependency, in which the inhibition increased slowly after depolarization to attain a steady-state value, while with (-)-PN200-110 and (+)-Bay K8644 the inhibition was almost instantaneous. To explain these observations, specific binding sites for dihydropyridines were studied in membranes isolated from rat aorta, using [3H](+)-PN200-110 as a radioligand. We found that the time course of the development of inhibition of potassium chloride-evoked contractions by various concentrations of (+)-PN200-110 paralleled the time course of [3H](+)-PN200-110 binding to isolated membranes and that the level of inhibition was predictable from the level of occupation of these binding sites. These results indicate that depolarization increases the affinity of calcium channels for dihydropyridines in vascular smooth muscle and that the time course of the inhibitory effect on contraction is determined by the time course of association with the high-affinity state of the channel.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1985

Subcellular localization of [3H]-nitrendipine binding sites in guinea-pig ileal smooth muscle.

The binding of [3H]-nitrendipine was studied in microsomal fractions isolated from guinea-pig ileal smooth muscle. Only one class of specific binding sites was detected, with a KD of 0.4 nM. For various dihydropyridine derivatives, including the stereoisomers of nimodipine and the 'Ca agonist' Bay K 8644, the potency for inhibition of [3H]-nitrendipine binding correlated well with the reported pharmacological potency in smooth muscle preparations. To establish the subcellular localization of [3H]-nitrendipine binding sites, untreated and digitonin-treated microsomal fractions were subfractionated by isopycnic density gradient centrifugation. The density distribution of [3H]-nitrendipine binding was markedly shifted by digitonin towards higher densities, as were the distributions of 5'-nucleotidase and [3H]-ouabain binding, whereas the distributions of NADPH:cytochrome c reductase and NADH:cytochrome c reductase were hardly modified by digitonin. It is concluded that most, if not all, [3H]-nitrendipine binding sites in guinea-pig ileal smooth muscle are present in the plasma membrane, in agreement with the postulated mode of action of dihydropyridines as inhibitors of plasmalemmal Ca channels.

5'-Nucleotidase↗
PubMed1983

Alteration of membrane barrier in stripped rough microsomes from rat liver on incubation with GTP: its relevance to the stimulation by this nucleotide of the dolichol pathway for protein glycosylation.

The membrane barrier of stripped rough microsomes from rat liver is markedly altered on incubation with GTP at 37 degrees C: after 30 min the structure-linked latency of mannose-6-phosphatase was considerably reduced, and esterase and nucleoside diphosphatase were partly released into the suspension medium. This phenomenon was already maximal with 30 microM GTP and was specific for this nucleotide. Similar conditions enhance the dolichol-mediated glycosylation of protein in microsomes incubated with uridine diphosphate N-acetylglucosamine and guanosine diphosphate mannose (Godelaine, D., H. Beaufay, M. Wibo, and A. Amar-Costesec, 1979, Eur. J. Biochem., 96:17-26; Godelaine, D., H. Beaufay, and M. Wibo, 1979, Eur. J. Biochem., 96:27-34). The GTP-induced permeability and glycosylation activities evolved in parallel in rough microsomes subjected to various treatments to detach the ribosomes and were maximal after removal of congruent to 60% of the RNA. In addition, GTP had no effect of this type in smooth microsome subfractions. Triton X-100, in spite of complex inhibitory effects on glycosylation reactions, mimicked the action of GTP by increasing the amount of microsomal dolichylphosphate that reacts with uridine diphosphate N-acetylglucosamine and by enhancing synthesis of dolichylpyrophosphoryl-chitobiose at concentrations greater than 2 mg/ml. Thus, GTP may activate dolichol-mediated glycosylation reactions in stripped microsomes by lowering the permeability barrier that prevents access of sugar nucleotides to the inner aspect of the membrane. The genuine role of GTP in the functioning of the endoplasmic reticulum membrane in situ remains unknown. Because GTP seems to act only on rough microsomes, we hypothesize that this role is somehow related to biosynthesis of protein by the rough endoplasmic reticulum.

Acid Anhydride Hydrolases↗