Reductive chain separation of botulinum A toxin — a prerequisite to its inhibitory action on exocytosis in chromaffin cells

Cleavage of the disulfide bond linking the heavy and the light chains of tetanus toxin is necessary for its inhibitory action on exocytotic release ofcatecholamines from permeabi1ized chromaffin cells [(1989) FEBS Lett. 242, 245-248; (1989) J. Neurochern., in press]. The related botulinum A toxin also consists of a heavy and a light chain linked by a disulfide bond. The actions ofboth neurotoxins on exocytosis were presently compared using streptolysin O-permeabilized bovine adrenal chromaffin cells. Botulinum A toxin inhibited Ca2 +-stimulated catecholamine release from these cells. Addition of dithiothreitollowered the effective doses to values below 5 nM. Under the same conditions, the effective doses of tetanus toxin were decreased by a factor of five. This indicates that the interchain S-S bond of botulinum A toxin must also be split before the neurotoxin can exert its effect on exocytosis

Ca2+-Stimulated Catecholamine Release from alpha-Toxin Permeabilized PC12 Cells

Two possible cellular pathways of catecholamines from the chromaffin vesicles of PC 12 cells to the surrounding medium are explored in this study. The direct one circumventing the cytoplasm can be activated in a-toxin-permeabilized cells with micromolar levels of free Ca2+. Catecholamine metabolites formed in the cytoplasm (i.e., 3,4-dihydroxyphenylacetic acid and 3,4-dihydroxyphenylethanol) are neither formed nor released from the cells under these conditions. However, when vesicular catecholamines were discharged into the cytoplasm by addition of the ionophore nigericin, such metabolites are formed and released into the medium independent of Ca2+. Both types of experiments provide direct evidence for the operation of Ca2+-induced exocytosis of dopamine and noradrenaline in permeabilized PC12 cells. The Ca2+ dependence of dopamine or noradrenaline release, as measured by the determination of the endogenous catecholamines using the high-performance liquid chromatography technique, exhibits two different phases. One is already activated below 1 pM free Ca2+ and plateaus at 1-5 pM free Ca2+, while a second occurs in the presence of larger amounts of free Ca2+ (10-100 pM). Ca2+-induced catecholamine release from the permeabilized cells can be modulated in different ways: It is enhanced by the phorbol ester 12-0-tetradecanoylphorbol 13-acetate and the diacylglycerol 1 -oleyl-2-acetylglycerol provided Mg*+/ATP is present, and it is inhibited by guanosine 5’-0-(3-thiotriphosphate). The latter effect is abolished by pretreatment of the cells with pertussis toxin but not by cholera toxin. Thus, it appears that Ca2+-induced exocytosis can be modulated via the protein kinase C system, as well as via GTP binding proteins

Aspects of open-flavour mesons in a comprehensive DSBSE study

Open-flavour meson studies are the necessary completion to any comprehensive investigation of quarkonia. We extend recent studies of quarkonia in the Dyson-Schwinger-Bethe-Salpeter-equation approach to explore their results for all possible flavour combinations. Within the inherent limitations of the setup, we present the most comprehensive results for meson masses and leptonic decay constants currently available and put them in perspective with respect to experiment and other approaches.Comment: 38 pages, 26 figures, 2 tables, revised according to reviewer comment

QCD sum rules for D and B mesons in nuclear matter

QCD sum rules for D and B mesons embedded in cold nuclear matter are evaluated. We quantify the mass splitting of D - D-bar and B - B-bar mesons as a function of the nuclear matter density; extrapolated to saturation density it is in the order of 60 and 130 MeV driven essentially by the condensates , and . The genuine chiral condensate , amplified by heavy-quark masses, enters the Borel transformed sum rules for the mass splitting beyond linear density dependence. Including strange quark condensates reveals a umerically smaller and opposite effect for the Ds - Ds-bar mass splitting.Comment: 16 pages, 8 figures, to be published; a broader range of condensate values is discussed (v2

Characterization of hormone and protein release from alpha-toxin- permeabilized chromaffin cells in primary culture

Addition of Staphylococcus aureus alpha-toxin to adult bovine chromaffin cells maintained in primary culture causes permeabilization of cell membrane as shown by the release of intracellular 86Rb+. The alpha-toxin does not provoke a spontaneous release of either catecholamines or chromogranin A, a protein marker of the secretory granule, showing the integrity of the secretory vesicle membrane. However the addition of micromolar free Ca2+ concentration induced the co-release of noradrenaline and chromogranin A. In alpha-toxin-treated cells, the released chromogranin A could not be sedimented and lactate dehydrogenase was still associated within cells, which provides direct evidence that secretory product is liberated by exocytosis. By contrast, permeabilization of cells with digitonin caused a Ca2+- dependent but also a Ca2+-independent release of secretory product, a dramatic loss of lactate dehydrogenase, as well as release of secretory product in a sedimentable form. Ca2+-dependent exocytosis from alpha- toxin-permeabilized cells required Mg2+-ATP and did not occur in the presence of other nucleotides. Thus alpha-toxin is a convenient tool to permeabilize chromaffin cells, and has the advantage of keeping intracellular structures, specifically the exocytotic machinery, intact

R-matrix approach to integrable systems on time scales

A general unifying framework for integrable soliton-like systems on time scales is introduced. The $R$-matrix formalism is applied to the algebra of $\delta$-differential operators in terms of which one can construct infinite hierarchy of commuting vector fields. The theory is illustrated by two infinite-field integrable hierarchies on time scales which are difference counterparts of KP and mKP. The difference counterparts of AKNS and Kaup-Broer soliton systems are constructed as related finite-field restrictions.Comment: 21 page