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M Schober

Publications and source records attributed to M Schober.

24 records · Page 2Linked to original sources
PubMed1985

Calcium channels: basic properties as revealed by radioligand binding studies.

The structural features and molecular properties of calcium channels have been explored with 1,4-dihydropyridines, d-cis diltiazem and verapamil in radiolabeled form. The concept of multiple (at least three) drug receptor sites of the channel (sites 1, 2, and 3) has been proposed. Site 1 is labeled by 1,4 dihydropyridines, site 2 by (+/-) verapamil (in skeletal muscle) and by (-) desmethoxyverapamil (in brain, skeletal muscle, and heart), site 3 by d-cis diltiazem (in skeletal muscle). The three distinct drug receptor sites communicate with each other via reciprocal allosterism and are linked to divalent cation binding sites. The concept of the reciprocal allosteric communication between the receptor sites has been proven by individual labeling of each of the drug receptor sites in the skeletal muscle t-tubule membrane where the density of calcium channels is extremely high. In brain and heart, labeling of the receptor sites 1 and 2 has also been successful. Three novel ligands for the calcium channel are presented: 125I-iodipine, a 1,4 dihydropyridine ligand, which has an exceptionally high specific activity (2,200 Ci/mmol), 3H-azidopine, a high-affinity, photoaffinity ligand and finally (-) 3H-desmethoxyverapamil, a high-affinity radioligand for receptor site 2. These ligands will aid in the isolation and final characterisation of the calcium channel. 125I-iodipine, 3H-azidopine and (-) 3H-desmethoxyverapamil bind to detergent-solubilized channels from skeletal muscle t-tubules. Whereas the 1,4-dihydropyridines label only a 12.9 S macromolecule, (-) 3H-desmethoxyverapamil additionally labels a approximately 5.0 S peak, where almost no high-affinity 1,4 dihydropyridine binding is found. Taken together with the results from target-size analysis experiments and photoaffinity labeling, an oligomeric structure of the channel is most likely. One polypeptide chain (Mr = 145,000) in reduced form has been unambiguously identified and is currently further characterized. It remains to be seen if the all of the earlier postulated four elements of the channel (alpha, beta, delta, gamma) are on different polypeptide chains or if the 145,000 peptide corresponds to the (beta, delta) or the (delta, gamma) element.

Affinity Labels↗
PubMed1984

(-)-[3H]Desmethoxyverapamil, a novel Ca2+ channel probe. Binding characteristics and target size analysis of its receptor in skeletal muscle.

(-)-[3H]Desmethoxyverapamil (2,7-dimethyl-3-(3,4-dimethoxyphenyl)-3-cyan- 7-aza-9-(3-methoxyphenyl)-nonanhydrochloride) was used to label putative Ca2+ channels in guinea pig skeletal muscle. The binding sites for (-)-[3H]desmethoxyverapamil co-purified with t-tubule membrane markers in an established subcellular fractionation procedure. (-)-[3H]Desmethoxyverapamil bound to partially purified t-tubule membranes with a KD of 2.2 +/- 0.1 nM and a Bmax of 18 +/- 4 pmol/mg membrane protein at 25 degrees C. Binding was stereoselectively inhibited by phenylalkylamine Ca2+ antagonists and in a mixed, non-competitive fashion by the benzothiazepine Ca2+ antagonist d-cis-diltiazem and the 1,4-dihydropyridine Ca2+ antagonist (+)-PN 200-110. Target size analysis of the (-)-[3H]desmethoxyverapamil drug receptor site revealed a molecular mass of 107 +/- 2 kDa. In contrast, the target size of the allosterically coupled benzothiazepine drug receptor site, labelled by d-cis-[3H]diltiazem, was 130.5 +/- 4 kDa (p less than 0.01) and of the 1,4-dihydropyridine binding site 179 kDa, when labelled with [3H]nimodipine. It is concluded that (-)-[3H]desmethoxyverapamil is an extremely useful radioligand for the phenylalkylamine-selective receptor site of the t-tubule localized Ca2+ channel which is allosterically linked to two other distinct drug receptor sites.

Animals↗
PubMed1984

Chromogranin immunoreactivity in the central nervous system. Immunochemical characterisation, distribution and relationship to catecholamine and enkephalin pathways.

Chromogranin A, the major soluble protein of the chromaffin granules, was isolated from bovine adrenals and used for immunization of rabbits. Chromogranin (CHR) immunoreactivity was studied by immunochemical and immunohistochemical methods in the adrenal, pituitary, brain and spinal cord of cattle, sheep, rats and guinea pigs using two antisera neither of which cross-reacted with dopamine beta-hydroxylase. Detailed studies were done using tissues from sheep only because very weak immunoreaction was obtained in tissues from the latter two species. Immunoblots of soluble proteins separated by two-dimensional polyacrylamide gel electrophoresis showed that the sera recognized a family of polypeptides in the adrenal which differed in size, but had almost identical isoelectric points. The patterns of immunoreactive proteins in extracts from the adrenal and pituitary were similar. Only two bands corresponding to the major high molecular weight bands in adrenal could be detected in the hippocampus which appeared to have a lower concentration of antigen. Other brain areas also showed two major immunoreactive proteins, one with a molecular weight similar to chromogranin A, and one smaller. Adrenal chromaffin cells, peripheral noradrenergic nerve axons and terminals in the pineal gland, a proportion of the anterior pituitary cells and the neurosecretory terminals of the posterior pituitary were strongly immunoreactive. In addition, CHR-immunoreactivity was widely distributed in the brain and spinal cord. The reactivity was readily visible in some nerve cell bodies and in well-defined pathways and terminal fibre networks. There were neurons whose perikarya were intensely stained but whose terminal projections appeared to be negative, while in other cases, the terminals appeared rich in CHR, while the perikarya were barely stained. All chromogranin immunoreactivity was abolished by absorption of the sera with a lysate from the chromaffin granules, but was not affected by absorption with Met- or Leu-enkephalin, dynorphin1-17, Met-enkephalin-Arg6-Phe7 or BAM-22P. Electron microscopic experiments revealed that the CHR-reaction in cell bodies was almost exclusively confined to the Golgi apparatus, while in synaptic boutons it was found in large dense-cored vesicles common to many types of terminals. In the hippocampal mossy fibre terminals, the immunoreactive granulated vesicles sometimes appeared to have fused with the plasma membrane of the boutons suggesting that the CHR was being secreted by exocytosis. The CHR-immunoreactivity was found to overlap partially with the distribution of many other neuroactive substances.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Medulla↗
PubMed1984

Biochemical and functional properties of large and small dense-core vesicles in sympathetic nerves of rat and ox vas deferens.

A comparative study of the noradrenaline storing vesicles in vas deferens from ox and rat was performed. Microsomal fractions were subjected to density gradient centrifugation. In rat, noradrenaline and dopamine beta-hydroxylase were mainly present in the upper fractions of the gradient, which is consistent with the predominance of light (small dense-core) vesicles in this species. In ox, noradrenaline, dopamine and dopamine beta-hydroxylase were found in the gradient in a bimodal distribution. This is consistent with the presence of about equal numbers of small and large dense-core vesicles in this species. On the other hand, chromogranin A, immunologically related proteins and enkephalin-like immunoreactivity were only present in the dense (large dense-core) vesicle population. In order to study the capability of light and dense vesicles to synthesize noradrenaline we "pulse-labelled" ox vasa deferentia with [3H]tyrosine. Already 3.5 min after the pulse both types of vesicles contained [3H]noradrenaline and [3H]dopamine. During longer "chase" periods the amount of [3H]dopamine gradually declined. We conclude that dense (large dense-core) vesicles contain chromogranin A, immunologically related proteins and enkephalin-like immunoreactivity whereas light (small dense-core) vesicles are devoid of these components. Both types of vesicles contain dopamine beta-hydroxylase and can synthesize noradrenaline from dopamine under in vivo conditions.

Animals↗
PubMed1981

[Bone scintigraphy in the diagnosis and follow up care of malignant head and neck neoplasms].

In diagnosis and localisation of malignant tumors with destruction of the bone, scintigraphy has its special importance in diagnosis as an addition to X-ray tomography. When carcinoma are localized in the middle or dorsal part of the base of the skull scintigraphy may help to calculate the chance for an operation. The exact knowledge of the dimension of the tumor is a valuable help in radiotherapy. In primary diagnosis of destructions of the base of the skull scintigraphy might give an earlier information than X-ray. Malignant tumors of the ear however are sufficiently detected by means of X-rays alone. The main field of scintigraphy is the observation of irradiated and operated malignoma. We recommend 6 or 12 months controls in combination with a clinical observation and with tomographic controls. Scintigraphy became a most valuable tool in the search and diagnosis of metastases in primary malignoma of the mammae, the lungs or the kidneys. In case of metastases in the skull scintigraphy is most helpful to detect them often earlier than by means of X-rays.

Adult↗