No abstract

Interleukin-1 (IL-1

The cytokine interleukin 1 (IL-1) is an important mediator of connective-tissue destruction in arthritic joints but the mechanisms by which IL-1 mediates signal transduction in chondrocytes is poorly understood. Previous results have indicated that IL-1 receptors co-localize with focal adhesions [Qwarnstrom, Page, Gillis and Dower (1988) J. Biol. Chem. 263, 8261-8269], discrete adhesive domains of cells that function in cell attachment and possibly in signal transduction. We have determined whether focal adhesions restrict IL-1-induced Ca2+ signalling in primary cultures of bovine chondrocytes. In cells grown for 24 h on fibronectin, the basal intracellular Ca2+ ion concentration ([Ca2+]i) was 100+/-3 nM. Optimal increases of [Ca2+]i above baseline were induced by 10 nM IL-1 (183+/-30 nM above baseline). There was no significant difference between cells plated on fibronectin or type II collagen (P>0.2; 233+/-90 nM above baseline). Ca2+ transients were significantly decreased by the inclusion of 0.5 mM EGTA in the bathing buffer (74+/-11 nM above baseline), and 1 microM thapsigargin completely blocked Ca2+ transients. Cells plated on poly-(l-lysine) or suspended cells showed no Ca2+ increases, whereas cells grown on fibronectin exhibited IL-1-induced Ca2+ responses that corresponded temporally to the time-dependent cell spreading after plating on fibronectin. Cells plated on poly-(l-lysine) and incubated with fibronectin-coated beads exhibited vinculin staining in association with the beads. In identical cell preparations, IL-1 induced a 136+/-39 nM increase of [Ca2+]i above baseline in response to 10 nM IL-1beta. There were no IL-1-induced Ca2+ increases when cells on poly-(l-lysine) were incubated with fibronectin-coated beads for only 15 min at 37 degrees C, in cells maintained for 3 h at 4 degrees C, in cells incubated with BSA beads for 3 h at 37 degrees C, or in cells pretreated with cytochalasin D. Labelling of IL-1 receptors with 125I-IL-1beta showed 3-fold more specific labelling of focal adhesion complexes in cells incubated with fibronectin-coated beads compared with cells incubated with BSA-coated beads, indicating that IL-1 receptor binding or the number of IL-1 receptors was increased in focal adhesions. These results indicate that, in chondrocytes, IL-1-induced Ca2+ signalling is dependent on focal adhesion formation and that focal adhesions recruit IL-1 receptors by redistribution in the cell membrane.

The influences of alloyed Lu, Hf and Cr on the oxidation and spallation behavior of NiAl were investigated. Although Lu has a "block effect" of Al as Hf does, the oxidation rate of Lu-doped NiAl is significantly higher, due to: (1) inhibitation of θ-to α-Al 2 O 3 transformation in early oxidation stage; (2) stronger scale grain refinement effect and enhanced oxygen transport rate. Segregation of S and C occurs not only at the alloy/scale interface, but also within the scale. Both Lu and Hf can significantly improve the scale adherence. However, This beneficial effect can be easily overcompensated by Cr.

A high performance NiCoCrAlY bond coat with dense dendritic microstructure was fabricated using laser powder deposition (LPD) technique. The thermally grown oxides (TGO) formed on the coating deposited by laser powder deposition is predominantly alumina instead of the mix oxides usually formed on the coatings prepared by air plasma spray and high velocity air fuel. Isothermal oxidation tests performed at 1150 °C reveal that the LPD bond coat shows significantly better spallation resistance and lower TGO growth rate. The superior spallation resistance of the TGO is further discussed in relation to the unique microstructure of the LPD bond coat.