Cytoplasmic Ca2+ has No Effect on the Excitability of Chara Plasmalemma

Internodal cells of Chara australis were subjected to two consecutiveintracellular perfusions with a Ca²⁺-free EGTA medium whichdisintegrated the tonoplast within about 10 minutes and thenwith a Ca²⁺-buffered medium. All perfusion media usually contained1 mM ATP. To stop the electrogenic pump, the internode was depletedof intracellular ATP. The excitability of the plasmalemma wasnot significantly influenced by intracellular free Ca²⁺ concentrationsup to 10^–4 M. To trigger action potentials, minimum currentdensities of 1 to 2 µA cm^–2 had to be applied atall tested Ca²⁺ concentrations. In the absence of cytoplasmicATP, excitability was completely lost at all Ca²⁺ concentrations. ¹ Present address: Botanisches Institut der Universit?t Bonn,Venusbergweg 22, D-5300 Bonn, FRG. (Received September 22, 1984; Accepted March 6, 1985)     

Brain gangliosides in monotremes, marsupials and placentals: phylogenetic and thermoregulatory aspects

The concentration and composition of brain gangliosides of 17 mammalian species belonging to the subclasses of Prototheria (monotremes), Metatheria (marsupials), and Eutheria (placentals) were investigated. The mean concentration of brain gangliosides ranges from 525 to 610 micrograms NeuAc/g wet wt in monotremes, 445-900 micrograms in marsupials and from 630 to 1130 micrograms in the placentals. In the phylogenetic series of mammals, a decrease in the complexity of brain ganglioside composition becomes obvious: a drastic reduction in the number of individual ganglioside fractions particularly those of the c-pathway of biosynthesis, took place from the level of monotremes to that of the marsupials and placentals. In monotremes, marsupials and "lower" placentals (insectivores) the percentage of alkali-labile gangliosides is relatively low (between traces and 5%), whereas in the higher evolved mammals it amounts to about 20% of all gangliosides. The ratio of the contents of the two major mammalian ganglioside fractions GD1a and GT1b is generally in the range of 1.0 and even higher; in the heterothermic platypus from the monotremes and in hibernators among the placental mammals, however, it is much lower (about 0.8). These data support the hypothesis that the brain ganglioside composition not only depends on the phylogenetic level of nervous organization (cephalization) but is additionally correlated with the state of thermal adaptation.     

Histochemische Darstellung Sialinsäure-haltiger Verbindungen im ZNS von Mäusen und Goldfischen mit der mPAT („milde“ Perjodsäure-Thionin)-Methode

Zusammenfassung An Gehirnproben von Goldfischen und Labormäusen wurde im Vergleich zu Speicheldrüsenproben (Glandula submandibularis) der Maus die milde Perjodsäure-Thionin (mPAT)-Methode für quantitative Untersuchungen zur histochemischen Lokalisation von Sialinsäure (NeuAc)-haltigen Verbindungen erprobt. Biochemische Gehaltsbestimmungen zeigten nach histologischer Aufarbeitung der Gewebe starke Auswagewebe, bedingt durch dessen höheren Gehalt an lipidgebundenen NeuAc, auswirkten. Eine vorherige KOH-Behandlung der Gewebe führte zu einer Erhöhung der Farbreaktion, was hauptsächlich auf O-acylierte NeuAc sowie möglicherweise auch auf Lactone in den NeuAc-Verbindungen hinweist. Nach Neuraminidase war eine Restfärbung von 45% im Gewebe, speziell im Tectum opticum von Goldfischen, zu beobachten. — Die Verwendung der mPAT-Färbung für eine spezifische und quantitative Darstellung der Gesamt-NeuAc-Verbindungen im ZNS erscheint nur bedingt geeignet, da im Gehirn im Vergleich zur Speicheldrüse zudem nur äußerst geringe NeuAc-Konzentrationen vorliegen, die infolgedessen nur schwache Farbreaktionen hervorrufen.

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Histochemical demonstration of sialic acid-containing compounds in the CNS of mice and goldfish by means of the mPAT (mild periodic acid-thionine)-method

Summary The mild periodic acid-thionine (mPAT)-method was examined for the quantitative research of histochemical localization of sialic acid (NeuAc)-containing compounds in brain samples of goldfish and albino mice in comparison to salivary gland (Glandula submandibularis) of the mouse. Biochemical determinations of NeuAc contents of the tissues showed that during histological treatment a significant decrease in the amount of lipid-bound NeuAc, especially in the brain had occurred, because of its high content of lipidbound NeuAc. A previous KOH-treatment caused in an increase of the colour reaction, which indicated mainly the amount of O-acylated NeuAc just as possibly lactone containing NeuAc-compounds. The intensity of staining, especially in the optic tectum of goldfish, decreased to 45% after neuraminidase-treatment. The low concentration of NeuAc-compounds in the brain in comparison to the salivary glands, results in only a faint staining. Therefore, the use of the mPAT-method seems to be not very suitable for a specific and quantitative staining of all NeuAc-compounds in the CNS.

     

Induction of fever in a teleost fish (Lepomis gibbosus, L.)

Although fishes are ectotherms they are nevertheless able to thermoregulate behaviorally by selecting appropriate water temperatures (1). In a temperature gradient fish will congregate to a species-specific range of preferred temperature (“final thermal referendum”) which is unaffected by previous thermal history of the individual (2,3). Several aquatic (and terrestrial) ectothermic vertebrates have been found to exhibit “behavioral fever” which is manifested as an increase in preferred temperature above the final thermal preferendum (4). Fever can be elicited by pyrogens: whole bacteria (alive or killed), components of bacterial cellwall (endotoxins), endogenous pyrogens, prostaglandins or from several other sources (5). Since the results with fever induction in fish using whole bacteria or endotoxins are very scarce the aim of the present work was to compare possible thermoregulatory effects of endotoxins and prostaglandins in the same species (Lepomis gibbosus, L.) by means of identical methods.     

Tumor suppressor IRF-1 mediates retinoid and interferon anticancer signaling to death ligand TRAIL

Retinoids and interferons are signaling molecules with pronounced anticancer activity. We show that in both acute promyelocytic leukemia and breast cancer cells the retinoic acid (RA) and interferon signaling pathways converge on the promoter of the tumoricidal death ligand TRAIL. Promoter mapping, chromatin immunoprecipitation and RNA interference reveal that retinoid-induced interferon regulatory factor-1 (IRF-1), a tumor suppressor, is critically required for TRAIL induction by both RA and IFNgamma. Exposure of breast cancer cells to both antitumor agents results in enhanced TRAIL promoter occupancy by IRF-1 and coactivator recruitment, leading to strong histone acetylation and synergistic induction of TRAIL expression. In coculture experiments, pre-exposure of breast cancer cells to RA and IFNgamma induced a dramatic TRAIL-dependent apoptosis in heterologous cancer cells in a paracrine mode of action, while normal cells were not affected. Our results identify a novel TRAIL-mediated tumor suppressor activity of IRF-1 and suggest a mechanistic basis for the synergistic antitumor activities of certain retinoids and interferons. These data argue for combination therapies that activate the TRAIL pathway to eradicate tumor cells.