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First principles simulations of steps on the -AlF3(100) surface between two, previously identified, low-energy terminations have been performed. The optimization of these structures leads to the formation of microfacets having the (010) orientation. The microfaceted surface is found to have a lower surface energy than either of the low-energy terminations used to construct the model stepped system. This suggests that the (100) surface is not, thermodynamically, the most stable termination of -AlF3. We have therefore also investigated the structure and stability of the (010) and (001) surfaces and find that both of these surfaces are lower in energy than the (100) surfaces. The surface energies of these planes are used to construct an approximate Wulff plot and thus predict the equilibrium crystal morphology.

Solid aluminium fluorides have great potential for use in a range of reactions that are catalysed by strong Lewis acids. However, very little is known about the detailed atomic scale structure of their surfaces. We present new results for the surface structure of β-AlF3based on first principles simulation and compare these with our earlier work on α-AlF3. On the basis of these simulations we can explain the observed reactivity of the aluminium fluoride materials. We can also use these results to postulate a mechanism for the observed high reactivity shown by amorphous, ‘high-surface area’ AlF3.

Algorithms that can robustly identify post-translational protein modifications from mass spectrometry data are needed for data-mining and furthering biological interpretations. In this study, we determined that a mass-based alignment algorithm (OpenSea) for de novo sequencing results could identify post-translationally modified peptides in a high-throughput environment. A complex digest of proteins from human cataractous lens, a tissue containing a high abundance of modified proteins, was analyzed using two-dimensional liquid chromatography, and data was collected on both high and low mass accuracy instruments. The data were analyzed using automated de novo sequencing followed by OpenSea mass-based sequence alignment. A total of 80 modifications were detected, 36 of which were previously unreported in the lens. This demonstrates the potential to identify large numbers of known and previously unknown protein modifications in a given tissue using automated data processing algorithms such as OpenSea. Keywords: proteomics • mass spectrometry • protein identification • bioinformatics • de novo sequencing • mass-based alignment • post-translational modification • human lens • crystallin • cataract

The ontogeny of the testicular mitogenic activity of Sprague Dawley rats was evaluated by stimulation in vitro of [3H]thymidine uptake and cell number in Swiss 3T3 and transformed NIH 3T3 fibroblasts. Addition of various amounts of testicular cytosolic protein resulted in a dose-dependent increase in cell number in both cell lines. The [3H]thymidine responses to testicular cytosolic proteins was also dose dependent but in a nonparametric manner. In addition, the responses of 3T3 cells to testicular cytosol was apparently dependent on the developmental stage of the testis, the time of stimulation, and the proliferative nature of the fibroblast cell line. These results suggest the presence of multiple forms of mitogenic substance in testicular cytosol and imply that the relative amounts of these substances may depend on the age of the donor animal. These substances may be important in the proliferation or differentiation of cell types at various stages of testicular development.

Karesek's demand-control model has been extremely influential and is widely used to predict a range of health outcomes, yet there have been comparatively few intervention studies and relatively little evidence of its impact on the design of work to improve health. This article discusses the tension between meeting the need for a model of psychosocial work factors and health outcomes which is simple enough to be theoretically useful in multidisciplinary research over a wide range of occupations yet is specific enough to generate useful information to influence policies and guide interventions. It is suggested that the success of the model in driving research has led to the neglect of a range of other psychosocial factors. Furthermore, while the appeal of the model lies in its apparent simplicity, variables are too broadly defined and complex to easily translate research findings into practical recommendations. To provide more practically useful evidence about risk factors, it is suggested that epidemiological studies should employ more clearly defined and specific variables incorporated in more complex psychosocial models which take into account the work context and the changing nature of work. © 1998 John Wiley & Sons, Ltd.

This study has focused on the characteristics of the Na+-K+-ATPase in in vitro preparations of vascular smooth muscle cells (VSMCs) derived from the rat carotid artery. The maximum velocity of enzyme reaction (Vmax) for the specific activity of the enzyme in the VSMCs' preparations was 2.36 +/- 0.04 (SE) mumol Pi X mg cell protein-1 X h-1 or 0.82 +/- 0.02 mumol Pi X 10(6) cells-1 X h-1. The activation of the enzyme by potassium, sodium and ATP has been investigated. The half-maximal values for potassium and sodium activation of the enzyme in the preparations were 1.18 and 10-20 meq/l, respectively. The respective Vmax values for potassium and sodium activation were reached at concentrations of 4-10 and 80-100 meq/l. The Michaelis constant for ATP was 0.83 mM. Calcium exerted a potent inhibition on the activity of the enzyme (I50 at 1 mM). It has been concluded that the Na+-K+-ATPase kinetic pattern in in vitro preparations of VSMCs is quite similar to that observed in homogenates or subcellular fractions of other tissues.

The number of Na+ pump units (Bmax) and the equilibrium dissociation constant (Kd) for ouabain as well as parameters of K+ binding to the Na+ pump were examined in in vitro-grown vascular smooth muscle cells ( VSMC ) derived from Sprague-Dawley rats. The technique to measure these variables utilizes analyses of [3H]ouabain displacement from its VSMC receptors by nonlabeled ouabain and K+. The mean values for Bmax and Kd in the cultured VSMCs were 1.95 X 10(5) receptor sites per single VSMC and 2.68 X 10(-6) M, respectively. The equilibrium dissociation constant for K+ (Ki) was 0.92 mM. K+ binding to the cultured VSMCs demonstrated positive cooperativity with a Hill coefficient (n) of 1.78.

Among the mouse-human hybrids prepared in our laboratory one clone was found to contain only human chromosome 5 with an integrated selectable marker. This monochromosomal hybrid was used to investigate different aspects related to the toxicity of diphtheria toxin (DT). The hybrid was as sensitive to diphtheria toxin as the human donor cells. The protective effect of NH4Cl against diphtheria toxin could be demonstrated in the hybrid and also in the mouse and human cell lines. The reversal of the protective NH4Cl effect at acid pH also could be demonstrated in all three cell types. Incubation of cells with 125I-diphtheria toxin at 37 degrees C in the presence of methylamine showed a time-dependent increase in specific association in the human and the hybrid but not in the mouse cell line. The results obtained for the first time on a stable monochromosomal hybrid suggest that chromosome 5 is both necessary and sufficient for the expression of DT sensitivity.

This study explores the relationship between extracellular calcium (Cao) and Na+-K+ regulation as it particularly pertains to the activity of the Na+ pump in cultured vascular smooth muscle cells (VSMCs) originating from Sprague-Dawley rats. As compared with cells incubated in media containing 0.5, 2.0, or 4.0 mM calcium, when the Na pump is active, VSMCs incubated in a Ca-deficient medium show a marked increase in intracellular sodium and no significant change in intracellular potassium. Associated with the rise in intracellular sodium there is an augmented activity of the Na pump. When the Na pump is inhibited, VSMCs incubated in either high-Ca medium (Cao = 4.0 mM) or Ca-deficient medium manifest a greater decline in intracellular potassium than cells incubated in media containing 0.5 or 2.0 mM calcium. Furthermore, when the Na pump is inhibited, VSMCs incubated in a Ca-deficient medium exhibit higher intracellular sodium levels in comparison with their counterparts incubated in media containing calcium. Flux experiments indicate that the aforementioned changes reflect increased membrane permeabilities to Na+ and K+. It is concluded that by regulating the permeability of the VSMC membrane, Cao plays an important role in the intracellular Na+-K+ homeostasis and that its effect on the Na pump is mediated via perturbations in the intracellular Na+ and K+ concentrations.

The binding of ouabain and K+ to the Na+ pump were analyzed in serially passed cultured vascular smooth muscle cells (VSMCs) originating from spontaneously hypertensive (SH), Wistar-Kyoto (WKY), and American Wistar (W) rats. Our techniques have utilized analyses of displacement of [3H]ouabain by both unlabeled ouabain and K+ from specific binding sites on the VSMCs. We have found that each of the VSMC preparations from the three rat strains appeared to demonstrate one population of specific ouabain receptors (Na+ pumps); the number of Na+ pump units (mean +/- SE, expressed as 10(5) units/cell; number of observations indicated in parentheses) of both the SH and WKY rats was significantly lower than the number of Na+ pump units of W rat VSMCs [SH: 3.00 +/- 0.02 (231), WKY: 2.87 +/- 0.05 (245), and W: 3.62 +/- 0.04 (225)]; the equilibrium dissociation constant values (microM) for ouabain in VSMCs of SH and WKY rats were similar but were significantly higher than that of VSMCs derived from W rats [SH: 4.69 +/- 0.09 (231), WKY: 4.57 +/- 0.12 (245), and W: 3.69 +/- 0.17 (225)]; and among the VSMCs originating from the three rat strains, the apparent equilibrium dissociation constant value for K+ (mM) was the lowest in those of the SH rat [1.04 +/- 0.003 (143), compared with VSMCs of the WKY rat [1.54 +/- 0.006 (135)] and W rat [1.19 +/- 0.003 (136)]. Our previous studies have demonstrated increased passive Na+ and K+ transport rate constants of SH rat VSMCs compared with either W or WKY rat cells. These findings suggest the possibility of higher permeabilities of the SH cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Na+-K+ passive transport and activity of the Na+ pump were examined in serially passed cultured vascular smooth muscle cells originating from spontaneously hypertensive (SH), Wistar-Kyoto (WKY), and Wistar (W) rats. Measurements included 22Na+ and 86Rb+ (K+ analogue) uptake and washout rate constants as well as intracellular Na+ and K+ levels. The aforementioned variables were studied in cells subjected to either 2 mM Ca2+ or Ca2+-deficient media. In 2 mM Ca2+ medium, SH rat cells demonstrated the highest exchange (uptake and washout) rate constants for Na+ and Rb+ (K+) among cells of the three rat strains. At this extracellular Ca2+ concentration, the Na+ pump activity of SH rat cells was higher than that of WKY rat cells and was not different from that of W rat cells. Incubation in Ca2+-deficient medium resulted in increased magnitudes of Rb+ washout and Na+ uptake rate constants in all cell preparations associated with elevated intracellular Na+ concentrations and augmented activity of the Na+ pump. Under this condition, cells derived from SH rats showed the highest Na+ uptake and Rb+ washout rate constants associated with the highest Na+ pump activity. The increase in intracellular Na+ level in Ca2+-deficient medium was the highest in SH rat cells. These findings show that innate membrane defects and the response of the Na+ pump to these abnormalities can be demonstrated in in vitro-grown vascular smooth muscle cells of the SH rat.