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At least 1,531 records · Page 85Linked to original sources
PubMed2000

Absorption of hydrophobic compounds into the poly(dimethylsiloxane) coating of solid-phase microextraction fibers: high partition coefficients and fluorescence microscopy images.

The use of solid-phase microextraction with poly(dimethylsiloxane) (PDMS)-coated glass fibers for the extraction and analysis of hydrophobic organic analytes is increasing. The literature on this topic is characterized by large discrepancies in partition coefficients and an uncertainty of whether highly hydrophobic analytes are retained by absorption into the fiber coating or by adsorption to the fiber surface. We applied a new method, which minimizes the impact of experimental artifacts, to determine PDMS water partition coefficients of 17 hydrophobic analytes including chlorinated benzenes, PCBs, PAHs, and p,p'-DDE. These partition coefficients are several orders of magnitude higher than some reported values. Two observations strongly suggest that the retention of hydrophobic organic substances is governed by partitioning into the PDMS coating. (1) The partition coefficients are proportional with octanol/water partition coefficients. (2) The fluorescence of fluoranthene was observed to be homogeneously distributed within the polymer coating when studied by means of fluorescence microscopy. Implications of these findings for the application of solid-phase microextraction with respect to potential detection limits, with respect to biomimetic extraction, and with respect to measurements in multicompartment systems are discussed.

Benzene↗
PubMedDate not supplied

Nanostructure of native pectin sugar acid gels visualized by atomic force microscopy.

Height and phase shift images of high methoxyl sugar acid gels (HMSAG) of pectin were obtained by atomic force microscopy in the tapping mode. Images revealed that pores in these gels were fluid and flattened out when measured as a function of time. These images revealed for the first time the structure of adsorbed sugar on pectin in the hydrated native gels and how the pectin framework is organized within these gels. Segmentation of images revealed that the underlying pectin framework contained combinations of rods, segmented rods, and kinked rods connected end to end and laterally. The open network of strands was similar to pectin aggregates from 5 mM NaCl solution imaged earlier by electron microscopy (Fishman et al., Arch. Biochem. Biophys. 1992, 294, 253). Area measurements revealed that the ratio of bound sugar to pectin was in excess of 100 to 1 (w/w). Furthermore, images indicated relatively small differences in the organization of native commercial citrus pectin, orange albedo pectin, and lime albedo pectin gels at optimal pH as determined in this study. The findings are consistent with earlier gel strength measurements of these gels. In addition, values of gel strength were consistent with values of molar mass and viscosity of the constituent pectins in that they increased in the same order. Finally, we demonstrated the advantage of simultaneous visualization of height and phase shift images for observing and quantitating the nanostructure of relatively soft gels which are fully hydrated with a buffer.

Citrus aurantiifolia↗
PubMed2003

Microcrystallization of indomethacin using a pH-shift method.

This study developed a microcrystallization process for indomethacin, a nonsteroidal anti-inflammatory drug (NSAID), using a pH-shift method in aqueous solution. The physicochemical properties of the microcrystals produced were similar to those of the standard crystalline powder in X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FT-IR) analyses, except for a lower XRD peak height and a slightly lower melting temperature (Tm) (1.5 degrees C). Phase contrast microscopy and scanning electron microscopy (SEM) showed that the indomethacin microcrystals were plate-like with a uniform size distribution (mean diameter =10.4+/-0.4 microm). In the initial phase, the dissolution rate of the indomethacin microcrystals was about 2.2 times higher than that of the standard crystalline powder. The biological activity of the indomethacin microcrystals was about 20% higher than that of the standard crystalline powder in their ability to inhibit the proliferation of colon cancer cells (HT-29).

Cell Survival↗
PubMed2001

The human kinesin-like protein RB6K is under tight cell cycle control and is essential for cytokinesis.

Several members of the kinesin superfamily are known to play a prominent role in the motor-driven transport processes that occur in mitotic cells. Here we describe a new mitotic human kinesin-like protein, RB6K (Rabkinesin 6), distantly related to MKLP-1. Expression of RB6K is regulated during the cell cycle at both the mRNA and protein level and, similar to cyclin B, shows a maximum during M phase. Isolation of the RB6K promoter allowed identification of a CDE-CHR element and promoter activity was shown to be maximal during M phase. Immunofluorescence microscopy using antibodies raised against RB6K showed a weak signal in interphase Golgi but a 10-fold higher signal in prophase nuclei. During M phase, the newly synthesized RB6K does not colocalise with Rab6. In later stages of mitosis RB6K localized to the spindle midzone and appeared on the midbodies during cytokinesis. The functional significance of this localization during M phase was revealed by antibody microinjection studies which resulted exclusively in binucleate cells, showing a complete failure of cytokinesis. These results substantiate a crucial role for RB6K in late anaphase B and/or cytokinesis, clearly distinct from the role of MKLP-1.

5' Untranslated Regions↗
PubMedDate not supplied

[Yeast peroxisomes, their development and operation].

Yeast peroxisomes (microbodies) were studied, particularly with yeast methylotrophs, using light-optical microscopy, viz. intravitam phase- and anoptral-contrast microscopy, with cytochemical as well as fixed and stained objects. The data obtained were compared with cytochemical as well as fixed and stained objects. The data obtained were compared with other evidence that we had gained on methylotrophs studied by electron microscopy and with the results obtained by investigating the peroxisomes of yeast cultures grown on nutrient containing other carbon sources. The activity of exocatalase and endocatalase, the enzymes characteristic of peroxisomes, was assayed at different growth phases of yeast methylotrophs and was found to be correlated with the cycle of development of peroxisomes. The content of biotin and inositol and its dynamics were studied in the methylotroph cells. Possible origin of peroxisomes is discussed as well as their development and the mechanism of degradation. A close contact and functional relationship have been established between peroxisomes and mitochondria.

Biotin↗
PubMed2001

Cellular overexpression of heme oxygenase-1 up-regulates p21 and confers resistance to apoptosis.

BACKGROUND: Induction of heme oxygenase-1 (HO-1) protects against diverse insults in the kidney and other tissues. We examined the effect of overexpression of HO-1 on cell growth, expression of p21, and susceptibility to apoptosis. METHODS: LLC-PK1 cells were genetically engineered to exhibit stable overexpression of HO-1. The effects of such overexpression on cell growth, the cell cycle, and the cell cycle-inhibitory protein, p21, were assessed; additionally, the susceptibility of these HO-1 overexpressing cells to apoptosis induced by three different stimuli (TNF-alpha/cycloheximide, staurosporine, or serum deprivation) was evaluated by such methods as the quantitation of caspase-3 activity, phase contrast microscopy, and the TUNEL method. RESULTS: HO-1 overexpressing LLC-PK1 cells demonstrated cellular hypertrophy, decreased hyperplastic growth, and growth arrest in the G0/G1 phase of the cell cycle. HO-1 overexpressing cells were markedly resistant to apoptosis induced by TNFalpha/cycloheximide or staurosporine as assessed by the caspase-3 activity assay. Such overexpression also conferred resistance to apoptosis induced by serum deprivation as evaluated by the TUNEL method; in these studies, inhibition of HO attenuated the resistance to apoptosis. Expression of the cyclin dependent kinase inhibitor, p21CIP1, WAF1, SDI1, as judged by Northern and Western analyses, was significantly increased in HO-1 overexpressing cells, and decreased as HO activity was inhibited. Moreover, this reduction in expression of p21 attendant upon the inhibition of HO activity in HO-1 overexpressing cells paralleled the loss of resistance of these cells to apoptosis when HO activity is inhibited. The pharmacologic inducer of HO-1, hemin, increased expression of p21 in wild-type cells and decreased apoptosis provoked by TNF-alpha/cycloheximide. CONCLUSION: Cellular overexpression of HO-1 up-regulates p21, diminishes proliferative cell growth, and confers marked resistance to apoptosis. We speculate that such up-regulation of p21 contributes to the altered pattern of cell growth and resistance to apoptosis. Our studies uncover the capacity of HO-1 to markedly influence the cell cycle in renal epithelial cells. In light of the profound importance of the cell cycle as a determinant of cell fate, we speculate that the inductive effect of HO-1 on p21 and the attendant inhibitory effect on the cell cycle provide a hitherto unsuspected mechanism underlying the cytoprotective actions of HO-1.

Animals↗
PubMed1984

Phagocytosis of hepatocyte mitochondria by rat Kupffer cells in vitro.

Kupffer cells in primary culture bind and endocytose rapidly added rat liver mitochondria. Using phase contrast microscopy various stages of the uptake and digestion of these organelles were documented. Activities of mitochondrial enzymes within the Kupffer cells increased during the early phase of phagocytosis; they later declined, reaching the endogenous level of the Kupffer cell mitochondria after 3 to 4 h. The uptake was enhanced in the presence of heparin or rat serum, while iodoacetate, cytochalasin B or anti-fibronectin antisera were inhibitory. The transient presence of enzymatically active hepatocyte mitochondria renders Kupffer cells capable of producing urea. This mechanism partially explains earlier observations of urea formation in non-parenchymal rat liver cells.

Animals↗
PubMed1985

Neodymium:YAG laser iridotomy in the cynomolgus monkey.

The histologic effects of various Neodymium:YAG laser energy levels were evaluated after iridotomy formation in cynomolgus monkey eyes. Scanning election microscopy of the corneal endothelium above the treated areas revealed no significant cell loss or pleomorphism when compared to the adjacent untreated areas. Light and phase contrast microscopy demonstrated closure of the iridotomies in most cases by a bridge of iris pigment epithelium. In several specimens, stromal tissue and pigment laden cells were present over the attenuated iris pigment epithelium. There were four lens opacities with rupture of the anterior lens capsule and anterior epithelial cell hyperplasia in one. No damage was apparent in the trabecular meshwork or retina with light microscopy or fluorescein angiography.

Animals↗