PubMed Health⌕ Search

Biomedical subjects

N Morel

Publications and source records attributed to N Morel.

At least 55 records · Page 3Linked to original sources
PubMed1997

Role of nitric oxide in the contractile response to 5-hydroxytryptamine of the basilar artery from Wistar Kyoto and stroke-prone rats.

1. Isolated basilar arteries from spontaneously hypertensive stroke-prone rats (SHRSP) are more sensitive to the contractile effect of 5-hydroxytryptamine (5-HT) than those from normotensive Wistar Kyoto rats (WKY). This has been attributed to a different proportion of 5-HT receptor subtypes mediating these responses. In the present study we have examined if differences in nitric oxide release could also contribute to this difference in sensitivity to 5-HT. 2. At rest, the normalized internal diameter was significantly smaller in SHRSP (297.4 +/- 3.5 microm, n = 88) than in WKY (375.1 +/- 4.0 microm, n = 62, P<0.01) arteries. The contractile response to 100 mM KCl was higher in WKY (3.57 +/- 0.15 mN mm(-1), n = 22) than in SHRSP arteries (2.32 +/- 0.20 mN mm(-1), n = 28, P<0.01). 3. When added on the plateau of contraction to 5-HT (1 microM), acetylcholine (ACh, 3 microM) evoked significant relaxation in all preparations from WKY (n = 20), but only in 15 out of 26 preparations from SHRSP. The mean relaxations were 55.4 +/- 5.2% in WKY and 20.6 +/- 4.6% in SHRSP (as % of the contractile tone evoked by 5-HT: P<0.01). 4. The NO synthase inhibitor N(omega)-nitro-L-arginine (L-NOARG, 0.1 mM) produced a similar increase in tone in both WKY and SHRSP. This tone was equal (in % of the contractile response to 100 mM KCl) to 70.8 +/- 4.4% in WKY (n = 20) and 67.6 +/- 5.9% in SHRSP (n=26) and was reversed by L-arginine (1 mM) and by 1,4-dihydropyridine calcium channel blockers (10 nM nisoldipine, 10 nM lacidipine, 100 nM nifedipine). The L-NOARG-induced tone was absent when the arteries were bathed in phosphate-free Krebs (pH 7.4). 5. EC50 values of 5-HT were about four fold smaller in SHRSP than in WKY arteries (P<0.01). The maximal response to 5-HT (Emax) was higher than 100 mM KCl-contraction in SHRSP but not in WKY arteries. Removal of endothelium produced a shift to the left of the 5-HT curve in WKY, but not in SHRSP arteries. 6. When evoked in phosphate-free Krebs, the contractile responses to 5-HT showed tachyphylaxis, but the responses were reproducible by adding the agonist at 30 min intervals. In such conditions, EC50 values of 5-HT were about two fold smaller in SHRSP than in WKY arteries (P<0.01). In phosphate-free Krebs, the blockade of NO synthase did not change the contractile response to 100 mM KCl; it reduced EC50 and increased Emax of 5-HT in WKY, but not in SHRSP. 7. These results confirm that the sensitivity to 5-HT is higher in basilar artery isolated from SHRSP than in those from WKY. They show that endothelium-dependent vasorelaxation to ACh is impaired in SHRSP. The finding that removal of endothelium or blockade of NO synthase augmented the contractile response to 5-HT in WKY, but not in SHRSP basilar arteries indicates that the difference in responsiveness to 5-HT observed between WKY and SHRSP basilar arteries might be, at least in part, related to dissimilarities in NO release. Furthermore, the L-NOARG-induced contraction sensitive to calcium channel blockers indicates that, in basilar arteries, NO production might lower L-type calcium channel opening and thereby control the tone of the vessels.

Acetylcholine↗
PubMed1997

Rapid anterograde axonal transport of the syntaxin-SNAP 25-VAMP complex.

During the process of docking and fusion of synaptic vesicles to the presynaptic membrane, several presynaptic proteins bind sequentially to a core complex associating two proteins of the presynaptic membrane, syntaxin and SNAP 25, and a protein of synaptic vesicles, VAMP/synaptobrevin. We have immunoprecipitated this core complex after CHAPS solubilization of pure cholinergic synaptosomes of Torpedo electric organ, using anti-syntaxin or anti-VAMP immunobeads. In parallel, we studied syntaxin and VAMP, which are transported by the rapid axonal flow to the nerve endings. We found that syntaxin and VAMP accumulating at the proximal end of an electric nerve ligature were already engaged in complexes, as in synaptosomes. In unligated nerves also, significant amounts of VAMP associate with syntaxin. The possibility that these complexes form after solubilization was eliminated because added VAMP was unable to associate with syntaxin in solubilized control nerves and because similar amounts of complex were obtained after sodium dodecyl sulfate or CHAPS solubilization. Hence, syntaxin is already associated with SNAP 25 and VAMP during axonal transport, before reaching nerve endings.

Animals↗
PubMed1997

[Preclinical study of the action of a calcium channel blocker during salt load].

Cardiovascular hypertrophy is a common feature of hypertension, but it is not known if this is related only to increased blood pressure or also to non-hemodynamic factors. Indeed, drug treatment of hypertension with hydralazine does reduce blood pressure but not cardiovascular hypertrophy. We used Stroke-prone rats (SHRSP) who are sensitive to salt load in order to better characterize the action of an antihypertensive agent on salt-dependent vascular hypertrophy and change in reactivity of calcium channels. SHRSP were submitted to salt load from 8 to 14 weeks of age with or without lacidipine, a long acting dihydropyridine. We observed that the cardiovascular hypertrophy was attenuated by lacidipine 0.3 mgkg-1 day-1 which did not change high blood pressure. The action of 1 mgkg-1 day-1 was higher on hypertrophy but, in addition, it reduced blood pressure. The salt-related increase in vascular responsiveness to the calcium channel activator Bay K 8644 was blunted by lacidipine treatment in both basilar and mesenteric arteries. By contrast with basilar artery, in mesenteric artery, this increased responsiveness was insensitive to bosentan, an endothelin antagonist but could be related to smooth muscle cell depolarization inhibited by lacidipine treatment. The present results confirm that lacidipine has blood pressure-independent effect on tissue remodeling in hypertension. They show that vascular response to salt is heterogeneous among vessels but is equally sensitive to lacidipine.

Animals↗
PubMed1996

Site-directed mutants designed to test back-door hypotheses of acetylcholinesterase function.

The location of the active site of the rapid enzyme, acetylcholinesterase, near the bottom of a deep and narrow gorge indicates that alternative routes may exist for traffic of substrate, products or solute into and out of the gorge. Molecular dynamics suggest the existence of a shutter-like back door near Trp84, a key- residue in the binding site for acetylcholine, in the Torpedo californica enzyme. The homology of the omega loop, bearing Trp84, with the lid which sequesters the substrate in neutral lipases displaying structural homology with acetylcholinesterase, suggests a flap-like back door. Both possibilities were examined by site-directed mutagenesis. The shutter-like back door was tested by generating a salt bridge which might impede opening of the shutter. The flap-like back door was tested by de novo insertion of a disulfide bridge which tethered the omega loop to the body of the enzyme. Neither type of mutation produced significant changes in catalytic activity, thus failing to provide experimental support for either back door model. Molecular dynamics revealed, however, substantial mobility of the omega loop in the immediate vicinity of Trp84, even when the loop was tethered, supporting the possibility that access to the active site, involving limited movement of a segment of the loop, is indeed possible.

Acetylcholinesterase↗
PubMed1996

Facilitation of the vasorelaxant action of calcium antagonists by basal nitric oxide in depolarized artery.

We investigated the effect of NO/cyclic GMP pathway on the action of calcium antagonists (isradipine, nisoldipine, lacidipine, verapamil, diltiazem) in rat aorta exposed to 100 mM KCl. For this purpose constitutive NO synthase was blocked by using 100 microM N omega-nitro-L-arginine (L-NNA). The steady-state contractile response evoked by 100 mM KCl was enhanced when the basal NO release had been blocked. The combined effects of basal NO release and calcium antagonists resulted in an inhibition greater than additive. Concentrations of calcium antagonists producing 50% inhibition of contraction were about 3-fold lower in the presence of the basal NO release than in its absence (P < 0.01). 45Ca2+ influx stimulated by 100 mM KCl was not affected by the basal NO release, but was inhibited by isradipine and verapamil regardless of NO blockade. Thus, the facilitation of the action of calcium antagonists by NO/cyclic GMP pathway seemed not to be accompanied by a modification of their action on L-type calcium channels. To confirm this, we measured the contractile tension and the calcium signal in fura-2 loaded rings, pretreated with either verapamil or verapamil plus 8-bromo cyclic GMP (BrcGMP), and further exposed to increasing concentrations of extracellular Ca2+ ([Ca2+]o) in 100 mM KCl solution. The increase in cytosolic Ca2- ([Ca2+]cyt) evoked by increasing ([Ca2+]o) in rings pretreated with verapamil alone was not different from rings pretreated with verapamil plus BrcGMP. In contrast, the [Ca2+]o-contraction curve was significantly shifted to the right in rings pretreated with verapamil plus BrcGMP. These results show that the NO/cyclic GMP pathway facilitates the inhibitory effect of calcium antagonists on 100 mM KCl-evoked contraction. This phenomenon is not related to a modification of calcium channel blockade, but could result from the reduction of the sensitivity of contractile machinery to Ca2+ by cyclic GMP.

Animals↗
PubMed1996

Inhibition by bosentan, an endothelin antagonist, of the hypersensitivity to Ca2+ channel activator evoked by salt-loading in basilar artery of stroke-prone spontaneously hypertensive rats.

High salt diet dramatically decreases the life time of spontaneously hypertensive stroke-prone rats (SHRSP). This has been related to an increase in the incidence of stroke. We have investigated the influence of high salt diet on the reactivity to the Ca2+ channel activator Bay K 8644 of basilar artery isolated from SHRSP. The results show that the sensitivity of basilar artery to Bay K 8644 was increased by salt load and that this hypersensitivity was blunted by bosentan, an ETA/ETB antagonist.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1996

Association of syntaxin with SNAP 25 and VAMP (synaptobrevin) in Torpedo synaptosomes.

Two proteins of the presynaptic plasma membrane, syntaxin and SNAP 25, and VAMP/ synaptobrevin, a synaptic vesicle membrane protein, form stable protein complexes which are involved in the docking and fusion of synaptic vesicles at the mammalian brain presynaptic membrane. Similar protein complexes were revealed in an homogeneous population of cholinergic synaptosomes purified from Torpedo electric organ by combining velocity sedimentation and immunoprecipitation experiments. After CHAPS solubilization, virtually all the nerve terminal syntaxin was found in the form of large 16 S complexes, in association with 65% of SNAP 25 and 15% of VAMP. Upon Triton X100 solubilization, syntaxin was still recovered in association with SNAP 25 and VAMP but in smaller 8 S complexes. A small (2-5%) percentage of the nerve terminal 15 kDa proteolipid subunit of the v-H+ATPase and of mediatophore was copurified with syntaxin, using two different antisyntaxin monoclonal antibodies. The use of an homogeneous population of peripheral cholinergic nerve terminals allowed us to extend results on the composition of the brain presynaptic protein complexes to the Torpedo electric organ synapse, a model of the rapid neuromuscular synapses.

Acetylcholine↗
PubMed1996

Breed differences in boar taint: relationship between tissue levels boar taint compounds and sensory analysis of taint.

A total of 228 intact male pigs form Duroc, Hampshire, Landrace, and Yorkshire breeds were used in the experiment. Samples of salivary gland and backfat were collected at slaughter for colorimetric assay of salivary and fat 16-androstene levels and fat skatole levels. Fat levels also were tested by a sensory panel using an R-index technique for detecting the presence of boar taint. The proportion of tainted carcasses determined by the sensory panel was 5.0% for androstenone and 11.4% for skatole, with a combined total of 15.0% tainted from either source. Sensory analysis of taint showed a lower proportion (P < .05) of tainted carcasses in Hampshire, with no difference in taint across the other three breeds. Analysis of taint compounds indicated that overall 14.5% of pigs had salivary gland 16-androstene levels and 20.9% had fat 16-androstene levels above acceptable limits. There was a higher (P < .05) proportion of Duroc pigs above the threshold levels for 16-androstenes in both salivary gland and fat. Landrace pigs had the lowest (P < .05) average tissue concentrations of steroids and skatole. Across breeds, only 1.8% of pigs had fat skatole concentrations above .25 ppm, which has been suggested as threshold levels of skatole for taint. The canonical correlation coefficient between fat compound levels and the R-indices of fat 16-androstenes and skatole was .40 (P < .001). Our results indicate breed differences in tissue levels of taint compounds and in taint assessed by a sensory panel. Levels of 16-androstene steroids were highly associated with taint, but more pigs had measured levels above the threshold than those identified as tainted by sensory analysis. Levels of fat skatole were low overall and did not account for all the pigs judged as tainted from skatole by sensory analysis.

Androstenes↗
PubMed1995

Evidence for a direct interaction of thapsigargin with voltage-dependent Ca2+ channel.

The effect of thapsigargin, an inhibitor of the sarco-endoplasmic reticulum Ca(2+)-ATPase, on voltage-dependent Ca2+ channels has been investigated in the A7r5 cell line and in membrane preparations from rat aorta, heart and brain. Patch-clamp technique showed that, at micromolar concentrations, thapsigargin inhibited the L-type Ca2+ channel current in A7r5 cells. It depressed the current at all voltages without change in the steady state inactivation curve. The rates of inactivation of the Ca2+ current were highly variable among the cells suggesting that more than one component of L-type Ca2+ current coexist in A7r5 cells, differing in the kinetics of inactivation. Thapsigargin appeared to be more potent on the slower-inactivating Ca2+ current than on the faster-inactivating one. In the same range of concentrations, thapsigargin inhibited the specific binding of 3H(+)-isradipine in intact cells while 45Ca2+ uptake in intracellular stores of skinned cells was inhibited at nanomolar concentrations. The equilibrium dissociation constant of 3H(+)-isradipine was increased in the presence of thapsigargin as a result of an increase of the dissociation rate constant indicating that the inhibitory effect of the antagonist cannot be attributed to a simple competitive interaction with the dihydropyridine binding site. Maximum binding capacity was unaffected. A similar pattern of inhibition of 3H(+)-isradipine binding was observed in membrane preparations from rat aorta, heart and brain. Those results indicate that, at micromolar concentrations, thapsigargin inhibits the voltage-dependent Ca2+ current by a direct interaction with the L-type Ca2+ channels.

Animals↗
PubMed1995

Effects of 8-bromo cyclic GMP and verapamil on depolarization-evoked Ca2+ signal and contraction in rat aorta.

1. The pharmacological action of NO donors is usually attributed to a cellular rise in guanosine 3':5'-cyclic monophosphate (cyclic GMP), but this hypothesis is based only on indirect evidence. Therefore, we have studied the effects of cyclic GMP on Ca2+ movements and contraction in rat isolated endothelium-denuded aorta stimulated by KCl depolarizing solution using the permeant analogue 8-bromo cyclic GMP (BrcGMP). Isometric contraction and fura-2 Ca2+ signals were measured simultaneously in preparations treated with BrcGMP and with verapamil. The activation of calcium channels was estimated by measuring the quenching rate of the intracellular fura-2 signal by Mn2+ and by the depolarization-dependent influx of 45Ca2+. 2. Stimulation with 67 mM KCl-solution evoked an increase in cytosolic Ca2+ concentration ([Ca2+]cyt) and a contractile response which were inhibited by pretreatment with verapamil (0.1 microM) or BrcGMP (0.1-1 mM). However, the inhibition of the fura-2 Ca2+ signal was significantly higher with verapamil than with BrcGMP, whereas the contraction was inhibited to a similar extent. 3. When preparations were exposed to K(+)-depolarizing solution in which the calcium concentration was cumulatively increased, the related increase in fura-2 Ca2+ signal was barely affected by BrcGMP, whereas the contractile tension was strongly and significantly inhibited. 4. Cellular Ca2+ changes were also estimated with 45Ca2+. 45Ca2+ influx in resting preparations was significantly reduced by BrcGMP (0.1 mM) but not by verapamil (0.1 microM); 45Ca2+ influx in KCl-depolarized preparations was reduced by verapamil but was unaffected by BrcGMP. 5. Measurements of Mn2+-induced quenching of the intracellular fura-2 signal showed that BrcGMPdid not affect divalent cation entry in K+-stimulated preparations, whereas verapamil concentration dependently inhibited Mn2+ entry stimulated by K+-depolarization.6. The present results indicate that BrcGMP did not affect voltage-dependent Ca2+ channel gating in the rat aorta. For a given fura-2 Ca2+ signal, the contraction was lower in preparations exposed toBrcGMP than in the untreated ones, suggesting that the activation of cyclic GMP-dependent kinases reduced the contractile efficacy of calcium. Furthermore, the reduction of depolarization-dependent 45Ca2+ uptake reported with sodium nitroprusside, a NO donor, was not observed with biologically active concentrations of BrcGMP, suggesting that this drug could have additional mechanisms of action,unrelated to activation of protein G-kinase.

Animals↗
PubMed1994

The endothelin ETA receptor antagonist, BQ-123, normalizes the response of SHR aorta to Ca2+ channel activator.

Hypertension is associated with a hypersensitive response to the Ca2+ channel activator, Bay K 8644. We investigated the effect of the endothelin ETA receptor antagonist, BQ-123, on the contractions induced by Bay K 8644 in aorta from spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats. BQ-123 (1 microM) decreased the sensitivity to Bay K 8644 of aorta of SHR down to that of WKY. This observation is consistent with a role for endothelin in hypertension.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1994

Characterization of aminopeptidase N from Torpedo marmorata kidney.

A major antigen of the brush border membrane of Torpedo marmorata kidney was identified and purified by immunoprecipitation. The sequence of its 18 N terminal amino acids was determined and found to be very similar to that of mammalian amino-peptidase N (EC 3.4.11.2). Indeed aminopeptidase N activity was efficiently immunoprecipitated by monoclonal antibody 180K1. The purified antigen gives a broad band at 180 kDa after SDS-gel electrophoresis, which, after treatment by endoglycosidase F, is converted to a thinner band at 140 kDa. This antigen is therefore heavily glycosylated. Depending on solubilization conditions, both the antigen and peptidase activity were recovered either as a broad peak with a sedimentation coefficient of 18S (2% CHAPS) or as a single peak of 7.8S (1% CHAPS plus 0.2% C12E9), showing that Torpedo aminopeptidase N behaves as an oligomer stabilized by hydrophobic interactions, easily converted into a 160 kDa monomer. The antigen is highly concentrated in the apical membrane of proximal tubule epithelial cells (600 gold particles/microns2 of brush border membrane) whereas no labeling could be detected in other cell types or in other membranes of the same cells (basolateral membranes, vacuoles or vesicles). Monoclonal antibodies prepared here will be useful tools for further functional and structural studies of Torpedo kidney aminopeptidase N.

Amino Acid Sequence↗
PubMed1994

Selective interaction of the calcium antagonist amlodipine with calcium channels in arteries of spontaneously hypertensive rats.

The mechanism of the antihypertensive action of the 1,4-dihydropyridine Ca2+ antagonist amlodipine was investigated by measuring dihydropyridine receptor occupation and the contractile responses to Ca2+ channel activation in aortas and mesenteric arteries from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) after chronic administration of amlodipine. Amlodipine treatment (10 mg/kg/day orally) significantly reduced the increase in blood pressure (BP) in SHR, but did not change BP in WKY. It more potently decreased the contractile response induced by Bay K 8644 in SHR than in WKY aorta. In both SHR and WKY arteries, the functional effect of chronic amlodipine treatment was related to occupation of the specific dihydropyridine binding sites similar to that which occurs after in vitro exposure to amlodipine 5 nM. Resting membrane potential (RMP) of aortic smooth muscle cells (SMC) from SHR was depolarized by 12 mV as compared with SMC from WKY, indicating that the higher potency of amlodipine in arteries from SHR could be related to the depolarization-induced increase in affinity for amlodipine of Ca2+ channels in SHR.

Administration, Oral↗
PubMed1993

Antisense probes against mediatophore block transmitter release in oocytes primed with neuronal mRNAs.

Antisense oligodesoxynucleotides were used to determine whether the mediatophore proteolipid is necessary for the Ca(2+)-dependent release of the neurotransmitter acetylcholine. Xenopus laevis oocytes were injected with poly(A)+ mRNAs extracted from the electric lobes of Torpedo marmorata. The electric lobes contain an homogeneous population of cholinergic neurons homologous to motoneurons. Addition of antisense probes hybridizing to the mediatophore 15 kDa subunit inhibited the expression of both the mediatophore proteolipid in oocyte membranes and the Ca(2+)-dependent acetylcholine release. Expression of other neuronal functions such as synthesis of [14C]acetylcholine from [14C]acetate was not inhibited. Another antisense probe specific for the sequence of a related proteolipid cDNA (the 15 kDa subunit of the chromaffin granule protonophore) was used as a control. It did not hybridize with the Torpedo mediatophore mRNA and, injected in addition to electric lobe mRNAs, it did not inhibit either mediatophore expression or acetylcholine release. We showed in addition that the mRNA primed oocytes did not contain a vesicular pool of acetylcholine. It was concluded (i) that the mediatophore proteolipid is essential for Ca(2+)-dependent acetylcholine release and (ii) that the cytosolic pool of neurotransmitter seems to be preferentially used in this system.

Acetylcholine↗