| 1. |
- Ravishankar, Raman, et al.
(författare)
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Physicochemical characterization of silicalite-1 nanophase material
- 1998
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 102:15, s. 2633-2639
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Tidskriftsartikel (refereegranskat)abstract
- A silicalite-1 nanophase material with an elementary particle size of 18-100 nm is synthesized from clear solution and isolated and purified using supercentrifugation. The nanopowder is characterized in detail using scanning electron microscopy, high-resolution transmission electron microscopy, attenuated force microscopy, 29Si magic angle spinning NMR, 13C cross polarization magic angle spinning NMR, X-ray diffraction, dinitrogen physisorption, and thermogravimetric analysis and compared with micrometer-sized silicalite-1. The nanosized and micrometer-sized materials have many common properties including the refined structure and the nature and concentrations of tetrapropylammonium species incorporated during the synthesis. Unique properties of the nanophase are a splitting of the characteristic framework vibration at 550 cm-1 into a doublet at 555 and 570 cm-1, a high concentration of defect sites, and a strain in the crystallites along the "a" crystallographic direction. The nanophase exhibits a two-stage dinitrogen physisorption in the low-pressure region, ascribed to adsorptions in micropores created by the stacking of the nanoparticles in addition to adsorptions in the intracrystalline micropores.
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| 2. |
- Barg, Sebastian, et al.
(författare)
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Different interactions of cardiac and skeletal muscle ryanodine receptors with FK-506 binding protein isoforms
- 1997
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Ingår i: American Journal of Physiology: Cell Physiology. - 1522-1563. ; 272:5 Pt 1, s. C1726-C1733
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, we compare functional consequences of dissociation and reconstitution of binding proteins FKBP12 and FKBP12.6 with ryanodine receptors from cardiac (RyR2) and skeletal muscle (RyR1). The skeletal muscle RyR1 channel became activated on removal of endogenously bound FKBP12, consistent with previous reports. Both FKBP12 and FKBP12.6 rebind to FKBP-depleted RyR1 and restore its quiescent channel behavior by altering ligand sensitivity, as studied by single-channel recordings in planar lipid bilayers, and macroscopic behavior of the channels (ryanodine binding and net energized Ca2- uptake). By contrast, removal of FKBP12.6 from the cardiac RyR2 did not modulate the function of the channel using the same types of assays as for RyR1. FKBP12 or FKBP12.6 had no effect on channel activity of FKBP12.6-depleted cardiac RyR2, although FKBP12.6 rebinds. Our studies reveal important differences between the two ryanodine receptor isoforms with respect to their functional interaction with FKBP12 and FKBP12.6.
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| 3. |
- Barg, Sebastian, et al.
(författare)
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The stimulatory action of tolbutamide on Ca2+-dependent exocytosis in pancreatic beta cells is mediated by a 65-kDa mdr-like P-glycoprotein
- 1999
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 96:10, s. 5539-5544
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Tidskriftsartikel (refereegranskat)abstract
- Intracellular application of the sulfonylurea tolbutamide during whole-cell patch-clamp recordings stimulated exocytosis >5-fold when applied at a cytoplasmic Ca2+ concentration of 0.17 microM. This effect was not detectable in the complete absence of cytoplasmic Ca2+ and when exocytosis was elicited by guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS). The stimulatory action could be antagonized by the sulfonamide diazoxide, by the Cl--channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), by intracellular application of the antibody JSB1 [originally raised against a 170-kDa multidrug resistance (mdr) protein], and by tamoxifen (an inhibitor of the mdr- and volume-regulated Cl- channels). Immunocytochemistry and Western blot analyses revealed that JSB1 recognizes a 65-kDa protein in the secretory granules. This protein exhibited no detectable binding of sulfonylureas and is distinct from the 140-kDa sulfonylurea high-affinity sulfonylurea receptors also present in the granules. We conclude that (i) tolbutamide stimulates Ca2+-dependent exocytosis secondary to its binding to a 140-kDa high-affinity sulfonylurea receptor in the secretory granules; and (ii) a granular 65-kDa mdr-like protein mediates the action. The processes thus initiated culminate in the activation of a granular Cl- conductance. We speculate that the activation of granular Cl- fluxes promotes exocytosis (possibly by providing the energy required for membrane fusion) by inducing water uptake and an increased intragranular hydrostatic pressure.
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| 4. |
- Bauer, M. K. A., et al.
(författare)
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Role of reactive oxygen intermediates in activation-induced CD95 (APO-1/Fas) ligand expression
- 1998
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Ingår i: Journal of Biological Chemistry. - : Elsevier BV. - 0021-9258 .- 1083-351X. ; 273:14, s. 8048-8055
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Tidskriftsartikel (refereegranskat)abstract
- Activation-induced cell death of T lymphocytes requires the inducible expression of CD95 (APO-1/Fas) ligand, which triggers apoptosis in CD95-bearing target cells by an autocrine or paracrine mechanism. Although execution of the CD95 death pathway is largely independent of reactive oxygen intermediates, activation-induced cell death is blocked by a variety of antioxidants. In the present study, we investigated the involvement of redox processes in the regulation of CD95 ligand (CD95L) expression in Jurkat T cells. We show that various antioxidants potently inhibited the transcriptional activation of CD95L following T cell receptor litigation or stimulation of cells with phorbol ester and ionomycin. Conversely, a prooxidant such as hydrogen peroxide alone was able to increase CD95L expression. As detected by Western blot and cytotoxicity assays, functional expression of CD95L protein was likewise diminished by antioxidants. Inhibition of CD95L expression was associated with a decreased DNA binding activity of nuclear factor (NF)-kappa B, an important redox-controlled transcription factor. Moreover, inhibition of NF-kappa B activity by a transdominant I kappa B mutant attenuated CD95L expression. Our data suggest that, although reactive oxygen intermediates do not act as mediators in the execution phase of CD95-mediated apoptosis, they are involved in the transcriptional regulation of CD95L expression.
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| 5. |
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| 6. |
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| 7. |
- Ferrari, D., et al.
(författare)
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Differential regulation and ATP requirement for caspase-8 and caspase-3 activation during CD95- and anticancer drug-induced apoptosis
- 1998
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Ingår i: Journal of Experimental Medicine. - : Rockefeller University Press. - 0022-1007 .- 1540-9538. ; 188:5, s. 979-984
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Tidskriftsartikel (refereegranskat)abstract
- Apoptosis is induced by different stimuli, among them triggering of the death receptor CD95, staurosporine, and chemotherapeutic drugs. In all cases, apoptosis is mediated by caspases, although it is unclear how these diverse apoptotic stimuli cause protease activation. Two regulatory pathways have been recently identified, but it remains unknown whether they are functionally independent or linked to each other. One is mediated by recruitment of the proximal regulator caspase-8 to the death receptor complex. The other pathway is controlled by the release of cytochrome c from mitochondria and the subsequent ATP-dependent activation of the death regulator apoptotic protease-activating factor 1 (Apaf-1). Here, we report that both pathways can be dissected by depletion of intracellular ATP. Prevention of ATP production completely inhibited caspase activation and apoptosis in response to chemotherapeutic drugs and staurosporine. Interestingly, caspase-8, whose function appeared to be restricted to death receptors, was also activated by these drugs under normal conditions, but not after ATP depletion. In contrast, inhibition of ATP production did not affect caspase activation after triggering of CD95. These results suggest that chemotherapeutic drug-induced caspase activation is entirely controlled by a receptor-independent mitochondrial pathway, whereas CD95-induced apoptosis can be regulated by a separate pathway not requiring Apaf-1 function.
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| 8. |
- Ferrari, D., et al.
(författare)
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P2Z purinoreceptor ligation induces activation of caspases with distinct roles in apoptotic and necrotic alterations of cell death
- 1999
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Ingår i: FEBS Letters. - : Elsevier. - 0014-5793 .- 1873-3468. ; 447:1, s. 71-75
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Tidskriftsartikel (refereegranskat)abstract
- Myeloic cells express a peculiar surface receptor for extracellular ATP, called the P2Z/P2X(7) purinoreceptor, which is involved in cell death signalling. Here, we investigated the role of caspases, a family of proteases implicated in apoptosis and the cytokine secretion. We observed that extracellular ATP induced the activation of multiple caspases including caspase-1, -3 and -8, and subsequent cleavage of the caspase substrates PARP and Iamin B. Using caspase inhibitors, it was found that caspases were specifically involved in ATP-induced apoptotic damage such as chromatin condensation and DNA fragmentation, In contrast, inhibition of caspases only marginally affected necrotic alterations and cell death proceeded normally whether or not nuclear damage was blocked. Our results therefore suggest that the activation of caspases by the P2Z receptor is required for apoptotic but not necrotic alterations of ATP-induced cell death. (C) 1999 Federation of European Biochemical Societies.
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| 9. |
- Timerman, A P, et al.
(författare)
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Selective binding of FKBP12.6 by the cardiac ryanodine receptor
- 1996
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Ingår i: Journal of Biological Chemistry. - 1083-351X .- 0021-9258. ; 271:34, s. 20385-20391
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Tidskriftsartikel (refereegranskat)abstract
- The calcium release channels (CRC)/ryanodine receptors of skeletal (Sk) and cardiac (C) muscle sarcoplasmic reticulum (SR) are hetero-oligomeric complexes with the structural formulas (ryanodine recepter (RyR)1 protomer)4(FKBP12)4 and (RyR2 protomer)4(FKBP12.6)4, respectively, where FKBP12 and FKBP12.6 are isoforms of the 12-kDa receptor for the immunosuppressant drug FK506. The sequence similarity between the RyR protomers and FKBP12 isoforms is 63 and 85%, respectively. Using 35S-labeled FKBP12 and 35S-labeled FKBP12.6 as probes to study the interaction with CRC, we find that: 1) analogous to its action in skeletal muscle sarcoplasmic reticulum (SkMSR), FK506 (or analog FK590) dissociates FKBP12.6 from CSR; 2) both FKBP isoforms bind to FKBP-stripped SkMSR and exchange with endogenously bound FKBP12 of SkMSR; and 3) by contrast, only FKBP12. 6 exchanges with endogenously bound FKBP12.6 or rebinds to FKBP-stripped CSR. This selective binding appears to explain why the cardiac CRC is isolated as a complex with FKBP12.6, whereas the skeletal muscle CRC is isolated as a complex with FKBP12, although only FKBP12 is detectable in the myoplasm of both muscle types. Also, in contrast to the activation of the channel by removal of FKBP from skeletal muscle, no activation is detected in CRC activity in FKBP-stripped CSR. This differential action of FKBP may reflect a fundamental difference in the modulation of excitation-contraction coupling in heart versus skeletal muscle.
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| 10. |
- Wiser, O, et al.
(författare)
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The voltage sensitive Lc-type Ca2+ channel is functionally coupled to the exocytotic machinery
- 1999
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Ingår i: Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 96:1, s. 248-253
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Tidskriftsartikel (refereegranskat)abstract
- Although N- and P-type Ca2+ channels predominant in fast-secreting systems, Lc-type Ca2+ channels (C-class) can play a similar role in certain secretory cells and synapses. For example, in retinal bipolar cells, Ca2+ entry through the Lc channels triggers ultrafast exocytosis, and in pancreatic beta-cells, evoked secretion is highly sensitive to Ca2+. These findings suggest that a rapidly release pool of vesicles colocalizes with the Ca2+ channels to allow high Ca2+ concentration and a tight coupling of the Lc channels at the release site. In binding studies, we show that the Lc channel is physically associated with synaptotagmin (p65) and the soluble N-ethylmaleimide-sensitive attachment proteins receptors: syntaxin and synaptosomal-associated protein of 25 kDa. Soluble N-ethylmaleimide-sensitive attachent proteins receptors coexpressed in Xenopus oocytes along with the Lc channel modify the kinetic properties of the channel. The modulatory action of syntaxin can be overcome by coexpressing p65, where at a certain ratio of p65/syntaxin, the channel regains its unaltered kinetic parameters. The cytosolic region of the channel, Lc753-893, separating repeats II-III of its alpha1C subunit, interacts with p65 and "pulls" down native p65 from rat brain membranes. Lc753-893 injected into single insulin-secreting beta-cell, inhibits secretion in response to channel opening, but not in response to photolysis of caged Ca2+, nor does it affect Ca2+ current. These results suggest that Lc753-893 competes with the endogenous channel for the synaptic proteins and disrupts the spatial coupling with the secretory apparatus. The molecular organization of the Lc channel and the secretory machinery into a multiprotein complex (named excitosome) appears to be essential for an effective depolarization evoked exocytosis.
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