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M Israël

Publications and source records attributed to M Israël.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1993

The effect of MR16728, a cetiedil analogue, on acetylcholine release in Torpedo synaptosomes.

MR16728, a cetiedil analogue, enhanced acetylcholine (ACh) release (up to 145% of control) from Torpedo synaptosomes when the release was triggered by a Ca2+ ionophore, A23187 or ionomycin, in the presence of 4 mM Ca2+ in the release medium, but inhibited ACh release induced by KCl depolarization of the presynaptic membrane. MR16728 also inhibited Ca(2+)-ATPase activity measured in purified synaptosomal presynaptic membranes. We studied the stimulation by MR16728 as a function of its concentration; the half-maximal effect was reached at the concentration of 13.5 microM. Moreover the stimulation was more pronounced (up to 300%) when a low concentration of Ca2+ (in the 10-micromolar range) was added to the medium. The enhancement of ACh release was also observed in proteoliposomes having incorporated mediatophore, a presynaptic membrane protein, able to release ACh in a Ca(2+)-dependent manner. Thus, mediatophore is a potential presynaptic target for MR16728.

Acetamides↗
PubMed1993

Glutamate and acetylcholine release from cholinergic nerve terminals, a calcium control of the specificity of the release mechanism.

We describe, in the present work, a continuous procedure for measuring the release of glutamate, and have applied it to analyze the co-release of glutamate and acetylcholine from cholinergic nerve terminals of electric organ synaptosomes. The two substances were measured in similar conditions using the two continuous chemiluminescent assays. The protein "Mediatophore" reconstituted in proteoliposomes was also able to translocate both transmitters with a preference for glutamate when the external calcium was increased between 3 and 10 mM. However, at lower calcium concentrations a clear preference for acetylcholine was found. For a regulated calcium entry as obtained by electrical stimulation of the nerve the release mechanism was fully specific for acetylcholine. Since the specificity of mediatophore depends on the local calcium amounts, the possible role of mediatophore at acetylcholine or glutamate specific synapses may be envisaged and is discussed in relation to the calcium control of specificity.

Acetylcholine↗
PubMed1993

Immunolabelling of the presynaptic membrane of Torpedo electric organ nerve terminals with an antiserum towards the acetylcholine releasing protein mediatophore.

Mediatophore is a nerve terminal membrane protein purified from Torpedo electric organ on its ability to translocate acetylcholine upon calcium action. An antiserum able to immunoprecipitate mediatophore activity was used to study the subcellular distribution of this protein. The presynaptic membrane exhibited a strong and discontinuous immunogold labelling, especially at the active zone where ACh is thought to be released. Two antigens were recognized on immunoblots of synaptosomal membranes: the 15-kDa subunit of mediatophore and a 14-kDa membrane protein that has a wide non-neuronal distribution. Antibodies purified from the serum on native mediatophore and monospecific towards the 15-kDa antigen still gave a high presynaptic membrane localized labelling. In addition, a few 14-kDa protein sites were present at the active zone. The Schwann cell finger interposed between the presynaptic membrane and the postsynaptic arch also exhibited the 14-kDa antigen raising the question of a possible interaction of mediatophore with the 14-kDa protein originating from the Schwann cell.

Acetylcholine↗
PubMed1992

Calcium-induced acetylcholine release and intramembrane particle occurrence in proteoliposomes equipped with mediatophore.

Proteoliposomes obtained from the mediatophore, a purified Torpedo electric organ nerve terminals protein, and endogenous lipids were used for a study of calcium-induced release of acetylcholine and freeze-fracture electron microscopy. Large intramembrane particles were induced by the influx of calcium into proteoliposomes, as previously observed for synaptosomes or stimulated electric organ nerve terminals. The involvement of mediatophore in a calcium dependent acetylcholine translocation seems therefore to be related to the occurrence of a category of intramembrane particles in the course of the release process.

Acetylcholine↗
PubMed1992

Effect of N,N'-dicyclohexylcarbodiimide on acetylcholine release from Torpedo synaptosomes and proteoliposomes reconstituted with the proteolipid mediatophore.

The mediatophore is a presynaptic membrane protein that has been shown to translocate acetylcholine (ACh) under calcium stimulation when reconstituted into artificial membranes. The mediatophore subunit, a 15-kDa proteolipid, presents a very high sequence homology with the N,N'-dicyclohexylcarbodiimide (DCCD)-binding proteolipid subunit of the vacuolar-type H(+)-ATPase. This prompted us to study the effect of DCCD, a potent blocker of proton translocation, on calcium-dependent ACh release. The present work shows that DCCD has no effect on ACh translocation either from Torpedo synaptosomes or from proteoliposomes reconstituted with purified mediatophore. However, using [14C]DCCD, we were able to demonstrate that the drug does bind to the 15-kDa proteolipid subunit of the mediatophore. These results suggest that although the 15-kDa proteolipid subunits of the mediatophore and the vacuolar H(+)-ATPase may be identical, different domains of these proteins are involved in proton translocation and calcium-dependent ACh release and that the two proteins have a different membrane organization.

Acetylcholine↗
PubMed1991

Evidence for an association of the 15-kDa proteolipid of mediatophore with a 14-kDa polypeptide.

The present report shows that mediatophore, a nerve terminal membrane protein that translocates acetylcholine on calcium action, forms a complex with a 14-kDa polypeptide. The complex was identified based on the following results. (a) A polyclonal antimediatophore antiserum that immunoprecipitates activity precipitates both the 15- and 14-kDa polypeptides. (b) After HPLC purification of mediatophore, both antigens were found in the same peak. (c) After 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate solubilization of presynaptic membranes or of the purified mediatophore, an immunoaffinity column made with the anti-14-kDa antigen monoclonal antibody retained both the 14-kDa and the 15-kDa polypeptide. Similarly, immunoprecipitation experiments using protein A-coated beads sedimented an immunocomplex in which both antigens were found. (d) The 14-kDa antigen could be localized in the synaptosomal membrane where mediatophore and its 15-kDa component are found.

Animals↗
PubMed1991

[Crisis intervention in a hospital setting: theoretical and practical aspects].

This paper explores the rationale for establishing a crisis intervention service in a psychiatric hospital setting. After reviewing the pertinent literature, a description will be provided for a crisis service that has been operating since 1987 in the psychiatric department of a general hospital. Data collected over a 6 month period will be presented in order to examine the types of patients referred to the service, the length of stay on the service and the follow-up. Our findings indicate that a large proportion of the patients referred to the service are diagnosed as having major psychiatric disorders and require some form of medical intervention. Nevertheless, a group of patients could be identified who benefit from traditional crisis intervention and who after receiving circumscribed treatment, require no hospital follow-up. The data will be utilized to outline the various roles that a crisis service can play in a psychiatric institution. The discussion will also focus on the structure and functioning of the service and its potential impact on the rest of the system.

Adolescent↗
PubMed1990

A 15 kDa proteolipid found in mediatophore preparations from Torpedo electric organ presents high sequence homology with the bovine chromaffin granule protonophore.

Upon SDS PAGE of isolated mediatophore, an acetylcholine-translocating protein, a doublet at 15 kDa was identified. Amino acid sequencing after CNBr cleavage gave a 17 residue-long peptide completely homologous with a sequence of the proton-translocating proteolipid from bovine chromaffin granules. A 51-mer oligodeoxynucleotide corresponding to this sequence was used to screen a library of electric lobe cDNAs constructed in lambda Zap II. A positive recombinant clone was isolated and found to encode the complete sequence of a 15.5 kDa protein highly homologous to the bovine chromaffin or yeast vacuolar ATPase proteolipid. In vitro translation of sense RNA transcripts of the clone indeed yielded a single 15 kDa proteolipid. Northern blot analysis showed that the 1.3 kb mRNA encoding this protein is significantly expressed in nervous tissues but not in electric organ or liver of Torpedo marmorata.

Acetylcholine↗
PubMed1990

Acetylcholine translocating protein: mediatophore at rat neuromuscular synapses.

The neuromuscular synapses of the rat sternomastoid muscles contain a membrane protein, mediatophore, that endows artificial membranes with a calcium-dependent acetylcholine release mechanism. Mediatophore and choline acetylase had similar distributions along the muscle. Sciatic nerve membranes contain mediatophore, and a purified preparation was obtained from the nerve.

Acetylcholine↗
PubMed1989

Effect of cetiedil analogs on acetylcholine and choline fluxes in synaptosomes and vesicles.

Cetiedil is a potent blocker of acetylcholine and choline fluxes. Several analogs of this compound have been synthesized and their effect on acetylcholine (ACh) and choline fluxes in synaptosomes and on ACh uptake in synaptic vesicles have been studied. The effects of these analogs were compared to those of other drugs acting on cholinergic functions. All these compounds were also studied in relation to the ACh translocating properties of the mediatophore, a protein recently purified from cholinergic nerve membranes and probably involved in the final step of release. We thus obtained a pattern of drug action for the three functions under study. The patterns of drug action on ACh release from synaptosomes or proteoliposomes were similar and clearly different from those for either synaptosomal choline transport or vesicular ACh uptake. In addition, the main outlines of the structure-function relationship for each of the functions studied, are described for cetiedil analogs.

Acetylcholine↗
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

Calcium-independent release of acetylcholine from electric organ synaptosomes and its changes by depolarization and cholinergic drugs.

Chemiluminescent detection was applied to measure the continuous spontaneous Ca2+-independent liberation of acetylcholine (ACh) from Torpedo electric organ synaptosomes. Differentiation between the release of ACh and choline was achieved by inhibiting cholinesterases with phospholine, and a way to quantify the continuous release was devised. The method permitted measurements during short time intervals from minute amounts of tissue and without an accumulation of ACh in the medium. Synaptosomes continuously liberated small amounts of ACh during incubations in the presence of 3 mM K+ and in the absence of Ca2+. The spontaneous liberation of ACh was similar both quantitatively and qualitatively at pH values of 8.6 and 7.8. It was unaltered by MgCl2 (10.4 mM), 2-(4-phenylpiperidino)cyclohexanol (10 microM), ouabain (104 microM), atropine (10 microM), and valinomycin (102 nM). Carbamoylcholine brought about a decrease, which could be partially reversed by atropine. The Ca2+-independent output of ACh was increased considerably when the concentration of K+ ions was raised (eightfold at 103 and 35-fold at 203 mM K+). Carbamoylcholine (104 microM) blocked the increase in ACh release produced by high K+; this effect of carbamoylcholine was not reversed by atropine (10 microM). When Ca2+ was added to synaptosomes depolarized by a high concentration of K+, the amount of ACh released during the first 1-3 min after the addition of Ca2+ was at least 20 times higher than in the absence of Ca2+, but the release returned rapidly to predepolarization values. Similarly high values of ACh release could be achieved by adding Ca2+ plus the ionophore A23187 and even higher values by adding Ca2+ plus gramicidin.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1987

Different effects of electrical stimulation of the mesencephalic and pontine reticular formation on the release of dopamine and acetylcholine in the cat caudate nucleus.

The effects of unilateral electrical stimulation of the pontine (PRF) and mesencephalic (MRF) reticular formation on the release of acetylcholine (ACh) and of [3H]dopamine continuously synthesised from [3H]tyrosine were examined in both caudate nuclei of halothane-anaesthetised cats implanted with push-pull cannulae. Stimulation of PRF led to a prolonged bilateral increase in the release of [3H]dopamine, whereas a significant reduction in [3H]amine release was observed in the ipsilateral caudate nucleus following stimulation of the MRF. Changes in ACh release were also seen, but they seemed to be independent from those in dopamine release: the release of ACh was enhanced markedly in both caudate nuclei following stimulation of the MRF, whereas a more moderate increase in the release of ACh occurred ipsilaterally following stimulation of the PRF. These data indicate that both the MRF and the PRF are involved in the control of dopaminergic and cholinergic transmission in the basal ganglia.

Acetylcholine↗
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↗