2,681 research outputs found
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 -matrix formalism is applied to the algebra of
-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
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