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  • 1
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Stimulation of β2-adrenergic receptors on the cell surface by adrenaline or noradrenaline leads to alterations in the metabolism, excitability, differentiation and growth of many cell types. These effects have traditionally been thought to be mediated exclusively by receptor ...
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Mitogenic lectins such as phytohaemagglutin (PHA) and con-canavalin A, and non-mitogenic lectins such as wheat germ agglutinin, lead to a rapid rise in [Ca2+]i even when there is no proliferative response9, and this hampers attempts to evaluate the requirement for an increase in [Ca2"^ in the ...
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  • 3
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] ES cells targeted at one calreticulin allele were engineered by inserting the PGKneo6 selection cassette in the antisense orientation at the calreticulin start site through homologous recombination (Fig. la)7. ES cells homozygous for the calreticulin mutation (double knockout) were isolated by ...
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  • 5
    ISSN: 1432-1424
    Keywords: intracellular pH ; cytoplasmic Ca2+ ; thymic lymphocytes ; chelator ; trace metals ; nigericin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effect of lowering intracellular pH on the membrane potential (E m ) of rat thymic lymphocytes was studied using the potential-sensitive dyebis-oxonol. Cells were acid loaded by addition of the electroneutral K+/H+ exchanging ionophore nigericin. Acidification to pH 6.3 in Na+-free solution resulted in a biphasic change inE m : an early transient hyperpolarization followed by a sustained depolarization. These changes were associated with a rise in cytosolic free Ca2+ ([Ca2+] i ). The hyperpolarization was eliminated when the change in [Ca2+] i was prevented using BAPTA, an intracellular Ca2+ chelator. Moreover, a similar hyperpolarization was elicited by elevation of [Ca2+] i at physiological pH i using ionomycin, suggesting involvement of Ca2+-activated K+ channels. In contrast, the depolarization phase could not be mimicked by raising [Ca2+] i with ionomycin. However, intracellular BAPTA effectively inhibited the acidificationinduced depolarization. Inhibition was also obtained by extracellular addition of EGTA or dithiothreitol, even when the external free Ca2+ concentration remained unaltered. These observations suggested a possible role of contaminating trace metals. Cytosolic acidification is envisaged to induce intracellular accumulation of one or more trace metals, which induces the observed changes inE m . Accordingly, similar changes inE m can be induced without acidification by the addition of small amounts of Cu2+ to the medium. The ionic basis of theE m changes induced by acidification and the significance of these observations are discussed.
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  • 6
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have compared some features of the resting and the insulin-stimulated uptake of α-aminoisobutyrate (AIB) in frog skeletal muscle. We found a substantial difference between the two processes, namely, that resting AIB uptake is Na-independent while the insulin-stimulated fraction of the AIB uptake is Na-dependent. Since the amino acid transport systems in frog skeletal muscle are poorly characterized, we have also surveyed some of their properties. One of the most interesting findings of this survey is that both the uptake and efflux of AIB are inhibited by low concentrations of PCMBS (parachloro-mercury-benzene sulfonic acid 5×10−5 m). In contrast, the carrier mediated transport of basic amino acids is neither inhibited by this mercurial agent nor accelerated by insulin. The action of PCMBS strongly suggests the presence of a critical sulfhydryl group in the amino acid carrier system utilized by AIB. This group is exposed to the outside solution since PCMBS penetrates cell membranes poorly, and in addition its inhibitory actions were reverted by agents that do not penetrate the cell membrane like albumin or glutathione.
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  • 7
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The [3H] phlorizin-binding component of brush border vesicles was enrichedin situ by negative purification. Several procedures, known to effect selective solubilization of membrane components, were used separately or in combination to remove proteins unrelated to the binding. Deoxycholate ruptured the vesicles and released 67% of their protein, thereby increasing the specific [3H] phlorizin-binding activity of the pellet three-to fourfold. Extracting the deoxycholate-pellets with either NaI or alkaline solutions released up to 38% of the deoxycholate-insoluble protein without significantly affecting phlorizin binding. The polypeptide composition of the membranes at the different stages was analyzed by NaDodSO4-polyacrylamide gel electrophoresis. A number of polypeptides present in the original vesicles could be ruled out as essential components of the [3H] phlorizin binding entity. Intact and deoxycholate-treated vesicles were subjected to proteolytic attack. Papain liberated sucrase and isomaltase from intact vesicles, but affected neither other Coomassiestained bands nor phlorizin binding. Neither the protein composition nor the binding properties of sealed vesicles were influenced by trypsin or chymotrypsin. However, all the proteolytic enzymes tested on deoxycholate-treated membranes substantially reduced [3H] phlorizin binding and produced concomitantly the disappearance of several bands from the electrophoretic profile. Pretreatment of vesicles with papain, followed by deoxycholate extraction and incubation in alkaline media, increased the specific binding activity of the membranes up to ninefold by removing close to 90% of the protein. A limited number of polypeptides are suggested as possible candidates for the glycoside-binding site of intestinal brush borders.
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  • 8
    ISSN: 1432-1424
    Keywords: platelets-secretory granules ; α-granules ; membrane isolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Porcine α-granules, prepared by a modification of pre-existing methods, were found to be essentially homogeneous by transmission electron microscopy. Freeze-fractured samples of isolated granules revealed numerous intramembranous particles on the EF (exoplasmic fracture) surface and to a lesser extent on the PF (protoplasmic fracture) surface whereas the PS (protoplasmic) surface was relatively smooth. The granules appear to be sealed, as evidenced by: a) the retention of their electron dense core material; b) the inability of impermeant labels to react with the granule contents, and c) the finding that the intragranular proteins are refractory to mild hydrolysis by externally added proteases. Membranes were isolated by alkali extraction of the granules and used for biochemical characterization. Approximately 87% of the protein, but only insignificant amounts of phospholipid were removed by this procedure, which yielded membrane vesicles devoid of the dense core. The membranes contain one major and several minor polypeptides of molecular weights ranging from 28,000 to 230,000, as determined by polyacrylamide gel electrophoresis. The major polypeptide contains carbohydrate residues. The exposure of specific proteins on the cytoplasmic surface of the granule membrane was determined by a combination of surface-specific labeling and proteolysis of intact granules, followed by membrane isolation and analysis. In sealed granules, only a limited number of bands are modified by the reagents whereas most of them are affected following granule lysis, indicating asymmetry in their transmembrane disposition. The fraction eluted by alkali extraction was also analyzed and found to contain nine major polypeptides of molecular weights ranging from 230,000 to 43,000. These are compared to the weights of the macromolecules believed to be secreted from α-granules, as determined by radioimmunological techniques.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 90 (1986), S. 1-12 
    ISSN: 1432-1424
    Keywords: antiport ; pH regulation ; volume regulation amiloride ; growth factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
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  • 10
    ISSN: 1573-4935
    Keywords: amiloride ; Na+/H+ exchange ; antiport ; superoxide ; leukocytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The cytoplasmic pH undergoes a biphasic change when neutrophils are activated. The role of Ca2+ in initiating these changes was investigated. No correlation was found between the increased cytosolic [Ca2+] and the stimulation of the Na+/H+ antiport. Similarly, the cytoplasmic acidification elicited by activation in Na+-free media was found to be unrelated to [Ca2+]. Reversal of Na+/H+ exchange was also ruled out as the source of the acidification. Data using a variety of soluble activators indicate that metabolic acid generation is largely responsible for the observed drop in cytoplasmic pH.
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