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N Morel

Publications and source records attributed to N Morel.

At least 91 records · Page 5Linked to original sources
PubMed1989

Pharmacological properties of voltage-dependent calcium channels in functional microvessels isolated from rat brain.

Voltage-operated calcium channels were studied in rat intracerebral microvessels. The contractile reactivity to KCl-depolarization was assessed by the measurement of internal diameter of superfused microvessels. Dihydropyridine receptor sites associated with calcium channels were identified and characterized using 3H(+)PN 200-110 [isopropyl-4-(2,1,3-benzodiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5- -methoxycarbonyl-pyridine-3-carboxylate]. Depolarization induced by high-KCl solution produced a marked reduction of the internal diameter of cerebral microvessels which was associated with the appearance of rhythmic activity. The vessel contraction was reversible and abolished by nimodipine. Binding studies with 3H(+)PN 200-110 revealed the existence of a single class of specific, stereoselective and voltage-dependent binding sites which bound (+)PN 200-110 with a KD of 88 +/- 6.6 pmol l-1 at 37 degrees C in microvessels incubated in NaCl medium. When microvessels were incubated in KCl-medium, the apparent KD value was reduced to 35 +/- 2 pmol l-1. Bmax was not significantly changed. The effect of KCl was not related to concomitant changes in the Na concentration. The potency of various dihydropyridine derivatives in inhibiting 3H(+)PN 200-110 binding was in agreement with their pharmacological potency in smooth muscle preparations. The effect of PN 200-110 and of nimodipine was stereoselective. Ki values of PN 200-110 and of nimodipine were increased in depolarized preparations, while nifedipine's potency was unchanged. Verapamil was only a partial inhibitor of 3H(+)PN 200-110 binding. The effect of diltiazem was stereoselective: the (+)-cis isomer enhanced the binding and the (-)-cis isomer of diltiazem poorly inhibited the binding of PN 200-110. Results showed that isolated cerebral microvessels possess functional voltage-operated calcium channels, which contain potential-modulated receptors for dihydropyridine calcium entry blockers with characteristics similar to those described in other tissues.

Animals↗
PubMed1989

The rapid induction by interleukin-2 of pulmonary microvascular permeability.

The clinical use of interleukin-2 (IL-2) is limited by severe cardiopulmonary dysfunction. This study examines the mechanism of respiratory failure related to IL-2, using sheep with chronic lung lymph fistulae. Awake animals were infused with an intravenous (I.V.) bolus of IL-2 10(5) U/kg (n = 5) or its excipient (EXC) control (n = 3), every 8 hours for 4 to 5 days. Cardiopulmonary function was monitored daily for at least one 8-hour period. Within 2 hours after each IL-2 administration, mean pulmonary arterial pressure (MPAP) rose. On Day 1, the mean rise was from 13 to 26 mmHg (p less than 0.05), and on Day 5, to 29 mmHg (p less than 0.05). MPAP returned to baseline levels after 2-3 hours. Pulmonary arterial wedge pressure was unchanged from 4 mmHg. There were transient falls in arterial oxygen tension, from 88 to 77 mmHg on Day 1 and to 73 mmHg (p less than 0.05) on Day 5. Lung lymph flow (QL) rose from 2.4 to 6.8 ml/30 minutes (p less than 0.05) on Day 1, and from 4.7 to 10.2 ml/30 minutes (p less than 0.05) on Day 5, whereas the lymph/plasma protein ratio increased on Day 1 from 0.69 to 0.83 (p less than 0.05) and from 0.63 to 0.71 (p less than 0.05) on Day 5. This documents an increase in pulmonary microvascular permeability. Thromboxane (Tx)B2 levels increased transiently after each IL-2 injection in plasma from 195 to 340 pg/ml (p less than 0.05) and in lung lymph from 222 to 772 pg/ml (p less than 0.05) on Day 1, and to similar levels on Day 5. There was a progressive rise in cardiac output from 5.7 to 8.6 1/minute (p less than 0.05) during the 5 days of infusion. Systemic blood pressure did not change. Temperature rose from 39.1 to 41.2 C (p less than 0.05), and shaking chills were common. There was a progressive fall in leukocyte count, from 8.4 to 3.2 X 10(3)/mm3 (p less than 0.05) by Day 5, reflecting a 77% fall in lymphocytes. Lung lymph lymphocyte counts rose, and lymphocyte clearance increased.(ABSTRACT TRUNCATED AT 250 WORDS)

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

Is the acetylcholine releasing protein mediatophore present in rat brain?

Mediatophore is a protein purified from the nerve terminal membranes of Torpedo electric organ. It confers to artificial membranes a calcium-dependent mechanism that translocates acetylcholine. When similar reconstitution experiments are applied to rat brain synaptosomal membranes they reveal the presence of mediatophore activity with properties close to those described for the Torpedo protein (extractability, sensitivity to calcium, and effect of the drug cetiedil). The activity was more abundant in synaptosomal membranes than in mitochondrial or myelinic membranes and in cholinergic areas as compared to cerebellum.

Acetylcholine↗
PubMed1988

Selective modulation by membrane potential of the interaction of some calcium entry blockers with calcium channels in rat mesenteric artery.

1. The effects of flunarizine, (+)-PN 200-110 and nifedipine on [3H]-(+)-PN 200-110 specific binding were investigated in intact rat mesenteric arteries bathed in physiological solution or in KCl-depolarizing solution, and in a membrane fraction from rat mesenteric arteries. 2. Unlabelled dihydropyridines, (+)-PN 200-110 and nifedipine, inhibited [3H]-(+)-PN 200-110 specific binding concentration-dependently in polarized as well as in depolarized intact arteries. The Ki value of (+)-PN 200-110 was decreased in arteries bathed in KCl-depolarizing solution compared to arteries bathed in physiological solution, while the Ki value of nifedipine was not significantly changed. Ki values measured in depolarized arteries were close to the IC50 values (concentrations inhibiting by 50% the KCl-contraction of rat mesenteric artery). 3. Flunarizine (10(-6) M) was unable to displace the specific binding of [3H]-(+)-PN 200-110 in intact arteries bathed in physiological solution. At 10(-7) M-10(-6) M, it inhibited the binding in depolarized arteries, suggesting that prolonged depolarization is required for the interaction of flunarizine with the dihydropyridine receptor. 4. In a membrane fraction isolated from rat mesenteric arteries, (+)-PN 200-110, nifedipine and flunarizine were all able to displace completely the specific binding of [3H]-(+)-PN 200-110. Displacement curves were parallel and Hill coefficients were close to unity. Ki values were close to the values obtained in depolarized intact arteries. 5. These results revealed a good correlation between the data obtained from binding tests and from pharmacological studies for dihydropyridine calcium entry blocking drugs, taking into account the time-dependence associated with their action on KCl-contraction compared to their binding properties. There was an important discrepancy between the concentrations of flunarizine active in binding studies and those active in pharmacological studies, which could be accounted for by the existence of multiple binding sites for calcium entry blockers in calcium channels.

Animals↗
PubMed1987

Histamine-operated calcium channels in intestinal smooth muscle of the guinea-pig.

The effects of Bay K 8644 and of nifedipine on histamine-induced mechanical and electrical responses were studied in the longitudinal smooth muscle of the ileum and in the taenia coli isolated from the guinea-pig. Nifedipine (10(-9)-10(-7) M) depressed the tonic and phasic components of histamine contraction. Phasic tension was less sensitive to nifedipine inhibition than was tonic tension (I50: 27 +/- 6 and 2.6 +/- 0.4 nM respectively). Bay K 8644 (10(-8)-10(-7) M) increased tension and rhythmic activity of intestinal smooth muscle and potentiated the histamine responses. The phasic tension evoked by histamine 10(-5) M and the phasic tension evoked by the KCl depolarizing solution showed the same sensitivity to nifedipine inhibition (I50: 28 +/- 5 nM) and were similarly potentiated by Bay K 8644. The tonic tension in response to the KCl-depolarizing solution was more sensitive to nifedipine inhibition than was the tonic tension in response to histamine and was not potentiated by Bay K 8644. These results indicate that different Ca entry pathways, dependent or not on modification of the membrane potential, are involved in the contractile response evoked by histamine in intestinal smooth muscle.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1987

Calcium-induced desensitization of acetylcholine release from synaptosomes or proteoliposomes equipped with mediatophore, a presynaptic membrane protein.

A "fatigue" of acetylcholine (ACh) release is described in cholinergic synaptosomes stimulated with the calcium ionophore A23187 or gramicidin. A small conditioning calcium entry, which did not trigger a large ACh release, led to a decrease of transmitter release elicited by a second large calcium influx. This fatigue was half-maximal at approximately 30 microM external calcium and developed in a few minutes. In contrast, activation of release by calcium was very rapid and was half-maximal at approximately 0.5 mM external calcium. Activation and desensitization of release could be attributed to the recently identified presynaptic membrane protein, the "mediatophore." Proteoliposomes equipped with purified mediatophore showed a calcium-dependent activation and "fatigue" of ACh release similar to that of synaptosomes. It was found that the ionophore A23187 rapidly equilibrated internal and external calcium concentrations in proteoliposomes. Thus, the external calcium concentration gave the internal concentration required for activation or desensitization of proteoliposomal ACh release. The mediatophore showed remarkable calcium binding properties (20 sites/molecule) with a KD of 25 microM. The physiological implications of desensitization on the organization of release sites are discussed.

Acetylcholine↗
PubMed1987

Cetiedil, a drug that inhibits acetylcholine release in Torpedo electric organ.

The effects of cetiedil, a vasodilatator substance with reported anticholinergic properties, were examined on cholinergic presynaptic functions at the nerve electroplaque junction of Torpedo marmorata using either synaptosomes or slices of intact tissue. Cetiedil abolished the calcium-dependent release of acetylcholine (ACh) triggered by depolarization or by addition of A23187 ionophore, a finding localizing the site of action downstream from the calcium entry step. In addition, a direct effect on the release process itself was indicated by the observation that cetiedil blocks the release of ACh mediated by a recently isolated presynaptic membrane protein, the mediatophore, reconstituted into ACh-containing proteoliposomes. In all three preparations, ACh release was inhibited by cetiedil with a Ki of 5-8 microM. Under the conditions used in these release experiments, the synthesis of ACh and its compartmentation within the nerve terminals were not modified. However, the drug was able to reduce high-affinity choline uptake and vesicular ACh incorporation when it was given together with the radioactive precursor, a result showing that cetiedil has a broad inhibitory action on cholinergic uptake processes.

Acetylcholine↗
PubMed1987

Prolonged depolarization increases the pharmacological effect of dihydropyridines and their binding affinity for calcium channels of vascular smooth muscle.

Experiments were performed on isolated rat mesenteric arteries with the calcium-antagonistic dihydropyridine derivative PN 200-110 in order to examine how its time-dependent effect on K+-evoked contraction might be related to voltage sensitive binding. (+)-PN 200-110 is a potent blocker of the K+-contraction in mesenteric artery. Inhibition of the K+-contraction was time-dependent and dose-effect curves were shifted to the left with the duration of depolarization. The (-)-isomer of PN 200-110 was less potent than the (+)-isomer but its action was also time-dependent. (+)-[3H]PN 200-110 binding has been determined in arteries bathed in physiological or high K+-solutions. Nonspecific binding measured in the presence of 10(-6) M nifedipine was not different in polarized and in depolarized arteries but specific binding was increased markedly after 30 min of depolarization. Specific binding data were well fitted by one hyperbolic curve describing a one-to-one binding to a single class of sites. Maximum binding capacity was unchanged whereas apparent dissociation constant was significantly lower in depolarized arteries. Depolarization also shifted to the left displacement curves of (+)-[3H]PN 200-110 by (+)- and (-)-PN 200-110. These results indicate that time-dependent effect of dihydropyridines in vascular smooth muscle is related to increased affinity of depolarized arteries for those drugs, suggesting that calcium channels in vascular smooth muscle are modulated by membrane potential in a way similar to that reported for cardiac muscle.

Animals↗
PubMed1987

[Cholinergic chemical transmission. Mechanisms of control].

The isolation of fractions of purified synaptic constituents has permitted to localize the enzymes involved in cholinergic mechanisms and to evaluate the acetylcholine concentration of vesicular stores and of the cytoplasmic pool where transmitter is synthetized. The isolation of cholinergic synaptosomes allowed study the mechanisms and regulations controlling the release process. The depletion of cytoplasmic acetylcholine elicited by stimulation is discussed in parallel to the role of synaptic vesicles. Presynaptic membrane proteins seem to be directly involved in the release of the transmitter.

Acetylcholine↗
PubMed1986

Purification of a presynaptic membrane protein that mediates a calcium-dependent translocation of acetylcholine.

A protein, which we call "mediatophore," that mediates calcium-dependent release of acetylcholine from proteoliposomes has been purified from the presynaptic plasma membrane. About 250 micrograms of this material was obtained from 500 g of Torpedo marmorata electric organ. Precipitation of the protein and subsequent removal of associated lipids inactivated the protein, which then became water soluble; this permitted evaluation of its Stokes radius (52 A) and its sedimentation coefficient (9.8 +/- 0.75 S) and, hence, an approximate molecular mass of 210 +/- 16 kDa could be determined. PAGE analysis showed that the protein is made of 17-kDa subunits, not linked by disulfide bonds. When this material was observed by electron microscopy after negative staining, the apparently pentameric structures had an average diameter of about 7 nm.

Acetylcholine↗
PubMed1986

Solubilization and partial purification of a presynaptic membrane protein ensuring calcium-dependent acetylcholine release from proteoliposomes.

In previous work, it was shown that cytoplasmic acetylcholine decreased on stimulation of Torpedo electric organ or synaptosomes in a strictly calcium-dependent manner. This led to the hypothesis that the presynaptic membrane contained an element translocating acetylcholine when activated by calcium. To test this hypothesis, the presynaptic membrane constituents were incorporated into the membranes of liposomes filled with acetylcholine. The proteoliposomes thus obtained released the transmitter in response to a calcium influx. The kinetics and calcium dependency of acetylcholine release were comparable for proteoliposomes and synaptosomes. The presynaptic membrane element ensuring calcium-dependent acetylcholine release is most probably a protein, since it was susceptible to Pronase, but only when the protease had access to the intracellular face of the presynaptic membrane. Postsynaptic membrane fractions contained very low amounts of this protein. It was extracted from the presynaptic membrane under alkaline conditions in the form of a protein-lipid complex of large size and low density which was partially purified. The specificity of the calcium-dependent release for acetylcholine was tested with proteoliposomes filled with equal amounts of acetylcholine and choline or acetylcholine and ATP. In both cases, acetylcholine was released preferentially. After cholate solubilization and gel filtration, the protein ensuring the calcium-dependent acetylcholine release was recovered at a high apparent molecular weight (between 600,000 and 200,000 daltons), its apparent sedimentation coefficient being 17S after cholate elimination. This protein is probably an essential coin of the transmitter release mechanism. We propose to name it mediatophore.

Acetylcholine↗
PubMed1985

Large-scale purification of presynaptic plasma membranes from Torpedo marmorata electric organ.

The presynaptic plasma membrane (PSPM) of cholinergic nerve terminals was purified from Torpedo electric organ using a large-scale procedure. Up to 500 g of frozen electric organ were fractioned in a single run, leading to the isolation of greater than 100 mg of PSPM proteins. The purity of the fraction is similar to that of the synaptosomal plasma membrane obtained after subfractionation of Torpedo synaptosomes as judged by its membrane-bound acetylcholinesterase activity, the number of Glycera convoluta neurotoxin binding sites, and the binding of two monoclonal antibodies directed against PSPM. The specificity of these antibodies for the PSPM is demonstrated by immunofluorescence microscopy.

Acetylcholinesterase↗
PubMed1985

Large-scale purification of Torpedo electric organ synaptosomes.

A procedure for the large-scale purification of Torpedo electric organ synaptosomes is described. The synaptosomal fraction obtained is very pure as judged from biochemical and morphological data. In addition, acetylcholine (ACh) release was demonstrated after KCl depolarization of synaptosomes in the presence of calcium. Two hundred grams of electric organ can be fractionated in a single run, allowing biochemical studies on presynaptic membrane constituents.

Acetylcholine↗
PubMed1984

Sodium/calcium exchange in smooth-muscle microsomal fractions.

The existence of Na+ -dependent Ca2+ transport was investigated in microsomal fractions from the longitudinal smooth muscle of the guinea-pig ileum and from the rat aorta, and its activity was compared with that of the plasmalemmal ATP-dependent Ca2+ pump previously identified in these preparations. The rate of Ca2+ release from plasmalemmal vesicles previously loaded with Ca2+ through the ATP-dependent Ca2+ pump was transiently faster in the presence of 150 mM-NaCl in the medium than in the presence of 150 mM-KCl or -LiCl or 300 mM-sucrose. Na+-loaded vesicles took up Ca2+ when an outwardly directed Na+ gradient was formed across the membrane. The Ca ionophore A23187 induced a rapid release of 85% of the sequestered Ca2+, whereas only 15% was displaced by La3+. Ca2+ accumulated by the Na+-induced Ca2+ transport was released by the addition of NaCl, but not KCl, to the medium. Ca2+ uptake in Na+-loaded vesicles was inhibited in the presence of increasing NaCl concentration in the medium. Half-maximum inhibition was observed with 28 mM-NaCl. Data fitted the Hill equation, with a Hill coefficient (h) of 1.9. Na+-induced Ca2+ uptake was a saturable function of Ca2+ concentration in the medium. Half-maximum activity was obtained with 18 microM-Ca2+ in intestinal-smooth-muscle microsomal fraction and with 50 microM-Ca2+ in aortic microsomal fraction. The results suggest that in these membrane preparations a transmembrane movement of Ca2+ can be driven by a Na+ gradient. However, the Na+-induced Ca2+ transport had a lower capacity, a lower affinity and a slower rate than the ATP-dependent Ca2+ pump.

Adenosine Triphosphate↗
PubMed1984

Reconstitution of a functional synaptosomal membrane possessing the protein constituents involved in acetylcholine translocation.

Reconstitution of a functional presynaptic membrane possessing calcium-dependent acetylcholine release properties has been achieved. The proteoliposomal membrane obtained gains its acetylcholine-releasing capabilities from presynaptic membrane proteins. At the peak of acetylcholine release, intramembrane particles became more numerous in one of the proteoliposomal membrane faces. This phenomenon resembles the intramembrane particle rearrangements found in stimulated synaptosomes. No visible structures capable of releasing acetylcholine as a result of the calcium influx were found inside the proteoliposomes. This supports the view that the release of free cytosolic acetylcholine from stimulated nerve terminals can be directly attributed to presynaptic membrane proteins. These proteins were extracted in a functional form from the synaptosomal membrane.

Acetylcholine↗