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At least 919 records · Page 51Linked to original sources
PubMed1986

Differential analysis of experimental hypermelanosis induced by UVB, PUVA, and allergic contact dermatitis using a brownish guinea pig model.

In moderately colored guinea-pig skin, UVB, PUVA, and allergic contact dermatitis were shown to induce hyperpigmentation that resembled the pigmentary changes observed in mongoloid human skin. Using this model, we examined the effects of chemical agents, including tyrosinase inhibitors and sunscreen agents, on the color changes induced by UV irradiation. The daily exposure of brownish guinea-pig skin to UVB irradiation at a variety of energies for 3 successive days induced clearly visible black pigmentation on the irradiated rectangular areas of the flank within a few days of irradiation, the maximum being reached about 1 week after irradiation, i.e., similar to the changes that occur in pigmented human skin. Split epidermal sheets prepared from untreated pigmented guinea pigs exhibited 200-400 melanocytes/mm2; 1 week after UV irradiation, the applied areas show an increased number of strongly dopa-positive melanocytes with stout dendrites (800-1,000 cells/mm2). UVA irradiation following an intraperitoneal injection of 8-methoxypsoralen (8-MOP) also produced black pigmentation 1 week after irradiation, and this was paralleled by a marked increase in the number of dopa-positive melanocytes in dopa-reacted split epidermal sheets. Allergic contact dermatitis produced by the application of 1-phenylazo-2-naphthol induced hyperpigmentation after an interval of about 14 days in 10 of the 21 allergy-acquiring animals examined. This induced pigmentation was accompanied by an increase in the number of dopa-positive melanocytes as compared to the number seen in controls. In contrast, allergic contact dermatitis produced by the application of dinitrochlorobenzene failed to induce such a high ratio of postpigmentation, with only 3 of the 21 allergy-acquiring animals showing hyperpigmentation and 5 showing depigmentation; in the latter, there was a slight decrease in the number of dopa-positive melanocytes. To study the preventive effect of tyrosine inhibitors on UVB-induced pigmentation, daily topical applications of these compounds were performed after three daily UVB irradiations. Treatment with 10% hydroquinone for 10 days interrupted UVB-induced pigmentation and resulted in a marked reduction in the number of epidermal melanocytes as compared to the number found in UVB-irradiated, untreated control skin.

Animals↗
PubMed2005

Impact of non-Legionella bacteria on the uptake and intracellular replication of Legionella pneumophila in Acanthamoeba castellanii and Naegleria lovaniensis.

In aquatic environments, Legionella pneumophila survives, in association with other bacteria, within biofilms by multiplying in free-living amoebae. The precise mechanisms underlying several aspects of the uptake and intracellular replication of L. pneumophila in amoebae, especially in the presence of other bacteria, remain unknown. In the present study, we examined the competitive effect of selected non-Legionella bacteria (Escherichia coli, Aeromonas hydrophila, Flavobacterium breve, and Pseudomonas aeruginosa) on the uptake of L. pneumophila serogroup 1 by the amoebae Acanthamoeba castellanii and Naegleria lovaniensis. We also investigated their possible influence on the intracellular replication of L. pneumophila in both amoeba species. Our results showed that the non-Legionella bacteria did not compete with L. pneumophila for uptake, suggesting that the amoeba hosts took in L. pneumophila through a specific and presumably highly efficient uptake mechanism. Living and heat-inactivated P. aeruginosa best supported the replication of L. pneumophila in N. lovaniensis and A. castellanii, respectively, whereas for both amoeba species, E. coli yielded the lowest number of replicated L. pneumophila. Furthermore, microscopic examination showed that 100% of the A. castellanii and only 2% of the N. lovaniensis population were infected with L. pneumophila at the end of the experiment. This study clearly shows the influence of some non-Legionella bacteria on the intracellular replication of L. pneumophila in A. castellanii and N. lovaniensis. It also demonstrates the different abilities of the two tested amoeba species to serve as a proper host for the replication and distribution of the human pathogen in man-made aquatic environments such as cooling towers, shower heads, and air conditioning systems with potential serious consequences for human health.

Acanthamoeba castellanii↗
PubMed1988

Sedimentation field flow fractionation of fused unilamellar vesicles: comparison with electron microscopy and gel filtration.

Sedimentation field flow fractionation (SF3), a relatively new instrumentation methodology for separating particles according to size, has been used to monitor changes in vesicle size during the formation of fused unilamellar vesicles of dipalmitoylphosphatidylcholine. The fusion of 500-A small unilamellar vesicles to 700-A large unilamellar vesicles (LUVs) and the slower conversion to 950-A LUVs at 4 degrees C was readily monitored by SF3 over the time course of a month. Changes in the physical state of these vesicles as a result of structural reorganizations were characterized by high sensitivity differential scanning calorimetry. The advantages and limitations of SF3 are discussed and correlated with electron microscopy and gel filtration.

Calorimetry, Differential Scanning↗
PubMed1976

Kinetics and stoichiometry of light-induced proton release and uptake from purple membrane fragments, Halobacterium halobium cell envelopes, and phospholipid vesicles containing oriented purple membrane.

We have used flash spectroscopy and pH indicator dyes to measure the kinetics and stoichiometry of light-induced proton release and uptake by purple membrane in aqueous suspension, in cell envelope vesicles and in lipid vesicles. The preferential orientation of bacteriorhodopsin in opposite directions in the envelope and lipid vesicles allows us to show that uptake of protons occurs on the cytoplasmic side of the purple membrane and release on the exterior side. In suspensions of isolated purple membrane, approximately one proton per cycling bacteriorhodopsin molecule appears transiently in the aqueous phase with a half-rise time of 0.8 ms and a half-decay time of 5.4 ms at 21degreesC. In cell envelope preparations which consist of vesicles with a preferential orientation of purple membrane, as in whole cells, and which pump protons out, the acidification of the medium has a half-rise time of less than 1.0 ms, which partially relaxes in approx. 10 ms and fully relaxes after many seconds. Phospholipid vesicles, which contain bacteriorhodopsin preferentially oriented in the opposite direction and pump protons in, show an alkalinization of the medium with a time constant of approximately 10 ms, preceded by a much smaller and faster acidification. The alkalinization relaxes over many seconds. The initial fast acidification in the lipid vesicles and the fast relaxation in the envelope vesicles are accounted for by the misoriented fractions of bacteriorhodopsin. The time constants of the main effects, acidification in the envelopes and alkalinization in the lipid vesicles correlate with the time constants for the release and uptake of protons in the isolated purple membrane, and therefore show that these must occur on the outer and inner surface respectively. The slow relaxation processes in the time range of several seconds must be attributed to the passive back diffusion of protons through the vesicle membrane.

Bacteriorhodopsins↗
PubMed1995

Surfactant lipids containing aromatic units produce vesicular membranes with high thermal stability.

Six new vesicle-forming, cationic surfactant lipids are synthesized. Four of them contain 'flat' aromatic units at different locations of hydrophobic segments. In order to estimate the influence of aromatic units in the lipid monomer two other surfactant lipids of related structure with n-butyloxy units in the places of aromatic groups were also prepared. Transmission electron microscopy confirmed the vesicular membrane formation from these newly synthesized lipids. DSC or temperature-dependent keto-enol tautomerism of benzoylacetanilide-doped vesicles reveal a remarkable increase in the thermal stability of the membranes formed from aromatic surfactant lipids in contradistinction to their counterparts that contain n-butyloxy units. The enhanced thermal stability originates presumably as a consequence of inter-monomer stacking.

Calorimetry, Differential Scanning↗
PubMed1984

Developmental analysis of the grandchildless (gs(1)N26) mutation in Drosophila melanogaster: abnormal cleavage patterns and defects in pole cell formation.

This article describes developmental analysis of gs(1)N26 mutation. gs(1)N26 is a temperature-sensitive maternal-effect mutation affecting the formation of the germ line (Y. Niki and M. Okada, Wilhelm Roux's Arch. Dev. Biol. 190, 1-10, 1981). At 25 degrees C, the cleavage nuclei do not divide synchronously and show various degrees of retarded migration to the posterior region. Blastoderm nuclei show antero-posterior mitotic waves; posterior yolk nuclei also are reduced in number at this stage. Pole cells form only when the cleavage nuclei migrate directly to the posterior pole. In fact, the posterior region of young eggs presents the usual ultrastructural features, and it is also able to participate in the formation of pole cells, as was proven by cytoplasmic transfer experiments. Therefore the defects in blastogenesis, in particular in the formation of pole cells of gs(1)N26 embryos, appear to result from the delayed migration of cleavage nuclei to the posterior pole.

Animals↗
PubMed1991

Purification and properties of the low-molecular-weight alpha-crystallin from normal goat lens: comparison with bovine lens.

Low-molecular-weight alpha-crystallin (alpha L-crystallin) isolated from decapsulated lens of goat (Capra hiscus) has been purified to an apparently homogeneous population. Goat alpha L-crystallin closely resembles its bovine counterpart in size, shape, exposition of sulfhydryl groups, subunit composition and the nature of its UV-absorption profile. Like bovine alpha L-crystallin, dissociated subunits of goat alpha L-crystallin assemble upon reassociation into a particle of almost half the size of the native one. However, subunits of goat alpha L-crystallin are found to contain more aromatic amino acid residues than those of bovine subunits leading to a higher value of extinction coefficient (E1cm1%) at 280 nm for the goat protein.

Amino Acids↗