Characterization of the inhibitory effect of glucocorticoids on the DNA replication of adult rat hepatocytes growing at various cell densities

Dexamethasone inhibited the basal and EGF-stimulated DNA synthesis of adult rat hepatocytes in primary culture. The inhibition was glucocorticoid-specific: It was shown by dexamethasone and hydrocortisone, but not by progesterone, testosterone, or estradiol; and was counteracted by the glucocorticoid antagonist RU-38486 in a concentration-dependent manner. Dexamethasone acted by decreasing the rate of entry into S-phase (kG1/S), while cell cycle parameters were unaffected. The steroid was able to decrease the kG1/S severalfold even when added more than 20 hr after EGF, half-maximal effect occurring 11 hr after the addition of dexamethasone. Densely populated areas were much more sensitive to the inhibition by dexamethasone than sparsely populated areas within the same culture dish: A moderate (10 nM) concentration of dexamethasone nearly abolished the DNA synthesis in densely populated areas of hepatocyte cultures with only marginal effect on sparsely populated cells.     

Coexpression of cytokeratin and vimentin in Rathke's cysts of the human pituitary gland

Summary Immunohistochemistry with monoclonal and polyclonal antibodies revealed the presence of cytokeratins in epithelial cells of Rathke's cysts in the pars intermedia of the human pituitary gland. With monoclonal antibodies specific for individual cytokeratins, the expression of CK 18, CK 8, CK 7, and CK 19 could be shown in these cells. Within the hypophysis, CK 19 and CK 7 were restricted to Rathke's cysts and a few epithelial cell clusters in the pars tuberalis, whereas other cytokeratins were also present in endocrine cells of the pars distalis. Furthermore, vimentin and, focally, glial fibrillary acidic protein (GFAP) were detected in the cystic epithelia. By double labelling, coexpression of cytokeratin and vimentin, GFAP and cytokeratin, and GFAP and vimentin could be demonstrated. Compiled data of all known cases of coexpression of cytokeratin and vimentin in normal cells reveal physiological correlations and suggest a functional significance of this rare type of coexpression of intermediate filament proteins.     

Variations in the cytoplasmic region account for the heterogeneity of the chicken MHC class I (B-F) molecules

Molecular variation among major histocompatibility complex (MHC) class I (B-F) proteins from B-homozygous chickens is apparently caused by C-terminal variation. Analysis of the total B-F protein pool revealed substantial heterogeneity with two or three molecular mass constituents, each being comprised by several isoelectric focusing variants. This heterogeneity could not be reduced by enzymatic deglycosylation. By contrast, proteolytic removal of a small (M _r 1000–4000) fragment from the chain resulted in the generation of a M _r 36 000 fragment, common to all the molecular mass variants. Unlike the parent proteins, the M _r 36 000 fragment derived from isolated variants yielded identical, simple patterns in two-dimensional gel electrophoresis and identical finger prints in peptide mapping. This, together with N-terminal amino acid sequencing, as well as comparison of hydrophobicity properties of fragments obtained by gradual proteolytic digestion, indicated that the small peptide responsible for the major B-F heterogeneity was situated in the intracellular, C-terminal part.     

Gramicidin in chromatophores of Rhodobacter sphaeroides

Chromatophores of Rhodobacter sphaeroides were excited with light flashes to generate a transmembrane electrical potential difference. The electric relaxation was measured by electrochromic absorption changes as a function of added gramicidin. At low gramicidin/bacteriochlorophyll (BChl) molar ratios the decay of the electrochromic absorption changes showed a biphasic behaviour, with a fast phase relaxing at some s, and a slow phase relaxing at more than 100 ms. This was attributable to a mixture of vesicles containing gramicidin dimers with others containing none. The concentration dependence of this effect was linear. This implied full dimerization of gramicidin. The data were interpreted to yield an average bacteriochlorophyll content per chromatophore of 770(±150) and the conductance of a single gramicidin dimer in the chromatophore membrane of 15(±4) pS (in about 115 mM KCl).Abbreviations BChl Bacteriochlorphyll - tricine N-Tris[hydroxymethyllmethylglycine Offprint requests to: W. Junge     

Statistic evaluation of the influence of species variation,culture conditions,surface wettability and fluid shear on attachment and biofilm development of marine bacteria

A budding coccoid bacterium, (CH1), a Vibrio sp. and a Pseudomonas sp. were investigated for factors governing their attachment to glass surfaces in static batch culture and laminar flow continuous culture systems. An analysis of variance showed that the three species exhibited very different responses. For CH1 attachment was dependent on cell density, incubation time and nutrient concentration. The Vibrio sp. was affected by nutrient concentration while the attachment of the Pseudomonas sp. was independent of cell density, incubation time and nutrient concentration. A comparison of attachment to hydrophilic and hydrophobic surfaces showed that attachment of the Vibrio sp. and CH1 to hydrophilic surfaces was 3 and 10 times greater respectively than to hydrophobic surfaces while Pseudomonas attached in equal numbers to both surfaces. The continuous culture system with defined flow hydrodynamics and growth conditions at steady state revealed a random sampling effect 3 times smaller than the batch culture system did. When the biofilm development of Pseudomonas sp. was followed during 46 h at different fluid shear under laminar and turbulent flow conditions, the former biofilm reached 3.3·10⁸ cells·cm^-2 and the latter 8.2·10⁷ cells·cm^-2.Non-common abbreviation NSS Nine salt solution     

Thylakoids from pea seedlings grown under intermittent light: biochemical and flash-spectrophotometric properties.

Thylakoid membranes were isolated from pea seedlings grown under intermittent light (2-min light/118-min dark cycles). These preparations differed from controls (thylakoids from plants grown under 16-h light/8-h dark cycles) in the following respects: 15 times smaller chlorophyll/protein ratio, 10 times greater chlorophyll a/b ratio, absence of light-harvesting chlorophyll a/b binding proteins, and 2-3-fold greater ratio of photosystem II over photosystem I. In addition we found the following: (1) Electrogenic electron transfer around cytochrome b6/f under flashing light was greatly enhanced, probably as a consequence of the greater photosystem II/photosystem I ratio. (2) The rate of proton uptake from the medium at the acceptor side of photosystem II was enhanced, probably by unshielding of the quinone binding domain. (3) The N,N'-dicyclohexylcarbodiimide sensitivity of the proton-pumping activity of photosystem II was absent, which was consistent with the attribution of a N,N'-dicyclohexylcarbodiimide-induced protonic short circuit to chlorophyll a/b binding proteins. (4) The sensitivity of oxygen evolution under continuous light to variations of pH or the concentration of Ca2+ was altered. Chlorophyll a/b binding proteins serve as light-harvesting antennas. We found in addition that they modulated the activity of water oxidation and, in particular, the proteolytic reactions around photosystem II.