Chronic effects of glucose on insulin signaling in A-10 vascular smooth muscle cells

To examine the effects of hyperglycemia on insulin signaling in A-10 vascular smooth muscle cells, cells were treated with extracellular D-glucose and effects of insulin were studied on the diacylglycerol-protein kinase C signaling system. A-10 cells specifically bound 125I-insulin, and insulin-like growth factor-I did not displace the label. 125I-insulin binding was unaltered under hyperglycemic conditions. To determine if insulin receptors were coupled to other insulin-regulated processes, diacylglycerol, protein kinase C, and glucose transport were evaluated. Insulin increased cellular diacylglycerol (DAG) levels which were also increased following glucose treatment and not further stimulated by insulin. The uptake of 2-[3H]deoxy-D-glucose (2-DOG) was stimulated by insulin and 12-O-tetradecanoyl phorbol 13-acetate (TPA). Insulin- and TPA-stimulated 2-[3H]DOG uptake was inhibited by a protein kinase inhibitor, staurosporine. Preincubation of cells with 500 nM TPA overnight resulted in the inhibition of insulin- and TPA-stimulated 2-[3H]DOG uptake. Protein kinase C activity was translocated from cytosolic to membrane fractions following insulin treatment. Overnight glucose (25 mM) treatment resulted in a 50% decrease in protein kinase C enzyme activity and > 90% decrease in protein kinase C beta immunoreactive levels. Protein kinase C activity and levels were not affected by osmotic control media containing mannitol. A-10 cells express GLUT4-type glucose transporters. Neither insulin-regulatable glucose transporter (GLUT4) mRNA nor GLUT4 protein levels were diminished by glucose. Significant decreases in insulin- and TPA-stimulated 2-[3H]DOG uptake occurred, however, with glucose. The down-regulation of protein kinase C beta and resultant inhibition of 2-[3H]DOG uptake by chronic glucose suggests a biochemical link between hyperglycemia and DAG-protein kinase C signaling in vascular smooth muscle cells.     

Kinetic trapping of oxygen in cell respiration

Cell respiration in eukaryotes is catalysed by mitochondrial enzyme cytochrome c oxidase. In bacteria there are many variants of this enzyme, all of which have a binuclear haem iron-copper centre at which O2 reduction occurs, and a low-spin haem, which serves as the immediate electron donor to this centre. It is essential that the components of the cell respiratory system have a high affinity for oxygen because of the low concentration of dissolved O2 in the tissues; however, the binding of O2 to the respiratory haem-copper oxidases is very weak. This paradox has been attributed to kinetic trapping during fast reaction of O2 bound within the enzyme's binuclear haem iron-copper centre. Our earlier work indicated that electron transfer from the low-spin haem to the oxygen-bound nuclear centre may be necessary for such kinetic oxygen trapping. Here we show that specific decrease of the haem-haem electron transfer rate in the respiratory haem-copper oxidase from Escherichia coli leads to a corresponding decrease in the enzyme's operational steady-state affinity for O2. This demonstrates directly that fast electron transfer between the haem groups is a key process in achieving the high affinity for oxygen in cell respiration.     

Clinical applications of fundus reflection densitometry

Fundus reflection densitometry or retinal densitometry is a non-invasive technique to examine the visual photopigment kinetics in living eyes. The technique is based on the comparison of the reflected light from the fundus in a fully light adapted eye (when all visual photopigment has been bleached) with the reflected light following complete dark adaptation (when the retina contains its maximum amount of visual photopigment). The technique provides a measure of the density of visual photopigment, its time constant of regeneration, its distribution and spectral characteristics if measured at a series of wavelengths. Fundus reflection densitometry in the human eye was introduced 40 years ago. Presently, it is the only available technique from which direct and objective insight can be obtained into visual photopigment. This knowledge is particularly relevant in eyes where abnormalities of photoreceptor function are suspected. This paper summarizes the current knowledge of fundus reflection densitometry in the diseased and in the aging human retina, gathered over the last 30 years. Considerable improvements of the instrument for clinical purposes have been obtained, and are also discussed.     

Cell cycle and genetic requirements of two pathways of nonhomologous end-joining repair of double-strand breaks in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, an HO endonuclease-induced double-strand break can be repaired by at least two pathways of nonhomologous end joining (NHEJ) that closely resemble events in mammalian cells. In one pathway the chromosome ends are degraded to yield deletions with different sizes whose endpoints have 1 to 6 bp of homology. Alternatively, the 4-bp overhanging 3' ends of HO-cut DNA (5'-AACA-3') are not degraded but can be base paired in misalignment to produce +CA and +ACA insertions. When HO was expressed throughout the cell cycle, the efficiency of NHEJ repair was 30 times higher than when HO was expressed only in G1. The types of repair events were also very different when HO was expressed throughout the cell cycle; 78% of survivors had small insertions, while almost none had large deletions. When HO expression was confined to the G1 phase, only 21% were insertions and 38% had large deletions. These results suggest that there are distinct mechanisms of NHEJ repair producing either insertions or deletions and that these two pathways are differently affected by the time in the cell cycle when HO is expressed. The frequency of NHEJ is unaltered in strains from which RAD1, RAD2, RAD51, RAD52, RAD54, or RAD57 is deleted; however, deletions of RAD50, XRS2, or MRE11 reduced NHEJ by more than 70-fold when HO was not cell cycle regulated. Moreover, mutations in these three genes markedly reduced +CA insertions, while significantly increasing the proportion of both small (-ACA) and larger deletion events. In contrast, the rad5O mutation had little effect on the viability of G1-induced cells but significantly reduced the frequency of both +CA insertions and -ACA deletions in favor of larger deletions. Thus, RAD50 (and by extension XRS2 and MRE11) exerts a much more important role in the insertion-producing pathway of NHEJ repair found in S and/or G2 than in the less frequent deletion events that predominate when HO is expressed only in G1.     

The anabolic effects of parathyroid hormone on cortical bone mass, dimensions and strength--assessed in a sexually mature, ovariectomized rat model

We examined the effect of the pineal neurohormone melatonin (MLT) on protection from viral encephalitis. The antiviral activity of MLT was evaluated in normal mice inoculated with Semliki Forest virus (SFV) and in stressed mice injected with the attenuated non-invasive West Nile virus (WN-25). Administration of MLT (s.c.) daily from 3 days before through 10 days after virus inoculation reduced viremia and significantly postponed the onset of disease and death by 7 to 10 days. Moreover, MLT injection reduced mortality of SFV (10 PFU) inoculated mice from 100% to 44%. In mice inoculated with high dose of SFV (100 PFU), MLT postponed death and reduced mortality by 20%. In all of the surviving mice anti-SFV antibodies were detected 22 days after virus inoculation. Infection of mice stressed by either isolation or dexamethasone injection with WN-25 induced mortality of 75% and 50% respectively, which was reduced by MLT administration to 31% and 25%, respectively. The efficiency of MLT in protecting from lethal viral infections warrants further investigations on its mechanisms of action.     

Identification of clinical yeast isolates by using the Microring YT

We investigated predisposing factors for the development of heterotopic ossification in a retrospective study of 637 hip arthroplasties, of which 484 were unilateral, 62 bilateral and 29 revision operations. The frequency of heterotopic ossification after a primary hip arthroplasty was 57 percent. In a univariate analysis, men, patients with hypertrophic arthrosis, and cemented arthroplasty were all at risk of developing heterotopic ossification. After a multivariate analysis, the male sex and the cemented arthroplasty remained as significant factors. In bilateral operations, the contralateral side developed heterotopic ossification in 82 percent when the primary hip operation had already caused ossification. There was no increase in ossifications after the contralateral operation. Half of the revision operations had an increase of heterotopic ossification from 1 to 4 Brooker classes.