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Biomedical subjects

S Johnsen

Publications and source records attributed to S Johnsen.

At least 37 records · Page 2Linked to original sources
PubMed1997

Identification and localization of a possible rhodopsin in the echinoderms Asterias forbesi (Asteroidea) and Ophioderma brevispinum (Ophiuroidea).

Protein extracts of optic cushion tissue from the asteroid Asterias forbesi and arm tissue from the ophiuroid Ophioderma brevispinum were subjected to Western blot analysis. Both tissues contain a membrane-associated protein that reacts with two monoclonal antibodies raised against bovine rhodopsin. This protein migrates slightly behind bovine rhodopsin during sodium-dodecyl-sulfate polyacrylamide gel electrophoresis, suggesting that its molecular weight is slightly larger. Immunohistochemical examination of the optic cushions of A. forbesi revealed a substance that reacts with both monoclonal antibodies; moreover, this substance is more abundant in dark-adapted animals than in light-adapted animals. The arms and central disk of O. brevispinum were also examined immunohistochemically. The tips of the arm spines contain a substance that reacts with both monoclonal antibodies, and at higher magnification this immunoreactive material is localized to small regions within the stroma of the ossicles. Taken together, the biochemical and immunochemical evidence suggests that the cross-reacting protein is homologous to other known rhodopsins and is serving as a visual pigment in echinoderms.

Amino Acid Sequence↗
PubMed1996

Synchronized Terrestrial-Atmospheric Deglacial Records Around the North Atlantic

On the basis of synchronization of three carbon-14 (14C)-dated lacustrine sequences from Sweden with tree ring and ice core records, the absolute age of the Younger Dryas-Preboreal climatic shift was determined to be 11,450 to 11,390 +/- 80 years before the present. A 150-year-long cooling in the early Preboreal, associated with rising Delta14C values, is evident in all records and indicates an ocean ventilation change. This cooling is similar to earlier deglacial coolings, and box-model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the North Atlantic heat conveyor, although the Younger Dryas may have begun as an anomalous meltwater event.

Journal Article↗
PubMed1994

Extraocular sensitivity to polarized light in an echinoderm.

This study tests the hypotheses that the birefringent calcite and stereom structure of the brittlestar (Ophiuroidea, Echinodermata) endoskeleton polarizes light and that certain brittlestars respond to polarized light. The first hypothesis was tested in Ophioderma brevispinum by examining ossicles from freshly killed specimens under polarized light. This analysis revealed that the lateral arm shields, oral arm shields, arm spines and aboral disk ossicles are dichroic and thus polarize light. The second hypothesis was tested in two orientation experiments under polarized light. The results from the first orientation experiment showed (1) that, under polarized light, animals oriented significantly and unimodally, (2) that, under polarized light with the e-vector perpendicular to that in 1, animals oriented significantly and unimodally to within 18 degrees of the bearing of the animals in 1, and (3) that, under unpolarized light, animals did not orient significantly. The results from the second orientation experiment showed that, under polarized light, animals oriented significantly and unimodally to within 17 degrees of an individual preference previously established under polarized light; but under unpolarized light, animals did not orient significantly to an individual preference established under polarized light. Thus, O. brevispinum orients under polarized, but not unpolarized, light. The unimodal orientation and lack of consistent alignment with the e-vector suggest that polarized light is not used as a directional cue but instead as a signal to sustain oriented behavior. The dichroism of the ossicles of O. brevispinum and the animal's capacity (though eyeless) to discriminate between polarized and unpolarized light suggest that the mechanism of polarization sensitivity may rely on polarizing filters built from the animal's skeleton.

Animals↗
PubMed1991

Coevolution to the edge of chaos: coupled fitness landscapes, poised states, and coevolutionary avalanches.

We introduce a broadened framework to study aspects of coevolution based on the NK class of statistical models of rugged fitness landscapes. In these models the fitness contribution of each of N genes in a genotype depends epistatically on K other genes. Increasing epistatic interactions increases the rugged multipeaked character of the fitness landscape. Coevolution is thought of, at the lowest level, as a coupling of landscapes such that adaptive moves by one player deform the landscapes of its immediate partners. In these models we are able to tune the ruggedness of landscapes, how richly intercoupled any two landscapes are, and how many other players interact with each player. All these properties profoundly alter the character of the coevolutionary dynamics. In particular, these parameters govern how readily coevolving ecosystems achieve Nash equilibria, how stable to perturbations such equilibria are, and the sustained mean fitness of coevolving partners. In turn, this raises the possibility that an evolutionary metadynamics due to natural selection may sculpt landscapes and their couplings to achieve coevolutionary systems able to coadapt well. The results suggest that sustained fitness is optimized when landscape ruggedness relative to couplings between landscapes is tuned such that Nash equilibria just tenuously form across the ecosystem. In this poised state, coevolutionary avalanches appear to propagate on all length scales in a power law distribution. Such avalanches may be related to the distribution of small and large extinction events in the record.

Biological Evolution↗
PubMed1990

Identification and characterization of plasma cells in normal human bone marrow by high-resolution flow cytometry.

The low frequency of plasma cells and the lack of specific cell surface markers has been a major obstacle for a detailed characterization of plasma cells in normal human bone marrow. Multiparameter flow cytometry enabled the identification of plasma cells in normal bone marrow aspirates. The plasma cells were located in a unique position in the correlation of forward light scattering, orthogonal light scattering, and immunofluorescent-labeled CD38. The identity of the sorted cell populations was confirmed by microscopic examination of Wright's stained slides and slides stained for cytoplasmic immunoglobulin using polyclonal antibodies reactive with light chains; ie, anti-kappa fluorescein isothiocyanate and anti lambda phycoerythrin (PE). The purity of the sorted plasma cells was greater than 97% (n = 4). The average frequency of plasma cells in normal bone marrow aspirates was low--0.25% of the nucleated cells (n = 7)--but surprisingly consistent between individuals (SD = .05; range 0.14% to 0.30%). A detailed analysis showed two distinct populations of plasma cells: (1) A population relatively smaller by forward light scattering expressed CD22, CD35, and sigE and was identified as early plasma cells (ie, lymphoplasmacytoid), and (2) a population larger by forward light scattering lacked these markers and was identified as mature plasma cells. The antigenic profile of the normal plasma cells was determined in two-color immunofluorescence studies. The expression of cell surface immunoglobulin G (IgG), IgA, IgE, IgD, IgM, and the cell surface antigens CD10, CD11b, CD13, CD11c, CD14, CD15, CD16, CD19, CD22, CD20, CD33, CD35, CD45, and HLA-DR was determined on the plasma cells. A significant heterogeneity in cell surface antigen expression was observed within the plasma cell population. Unexpectedly, myeloid-specific cell surface antigens such as CD33 and CD13 and the early B-cell antigen identified by CD10 were expressed on a proportion of plasma cells. These observations imply that the association of myeloid and early B-cell markers described in multiple myeloma may not be associated with the neoplasia but is a normal phenomenon.

ADP-ribosyl Cyclase↗
PubMed1989

Formation of chlorinated PAH--a possible health hazard from water chlorination.

Four PAH compounds, fluorene, anthracene, fluoranthene and benzo(a)pyrene were dissolved in humus poor (lake) and humus rich water. The samples were chlorinated, stored for three days, and extracted with cyclohexane. Chlorinated derivatives of the four compounds were synthesised and used as calibration standards for quantitative analysis of the corresponding chlorinated PAH formed during the experiment. The synthesized chlorinated PAH were tested for mutagenic activity by the Ames test, and their octanol/water partition coefficient (Pow) were determined by thin layer chromatography. Chlorinated fluorene, fluoranthene and benzo(a)pyrene were formed during chlorination of PAH polluted lake water, but not during chlorination of the humus rich water samples. All chlorinated PAH except 9,10-dichloroanthracene, acted as strong mutagens both in the presence and in the absence of metabolic activation, while benzo(a)pyrene was the only mutagen active parent PAH. The determined Pow showed high lipophilicity for all chlorinated PAH. Theoretically determined bioconcentration factors (BCF) were found to be extremely high, and increased with increasing ring number and increasing number of chlorine atoms attached to the ring.

Anthracenes↗
PubMed1989

Influence of natural aquatic humic substances on the bioavailability of benzo(a)pyrene to Atlantic salmon.

Uptake and bioconcentration factors of benzo(a)pyrene (BaP) in Atlantic Salmon were determined in water containing natural aquatic humic substances (AHS) and control water with low humic content by measuring rate constants for uptake and depuration. The amounts of partition-like and strongly AHS bound BaP were determined by tube dialysis and cyclohexane extraction, respectively. Uptake and bioconcentration factors (BCF) were observed to decrease in the presence of AHS, the values of the BCFs being 2310 and 1160 for control water and AHS respectively. The rate constant for uptake of AHS bound BaP was found to be 30 percent of that of free dissolved BaP.

Animals↗
PubMed1989

Effects of humus concentrations on benzo[a]pyrene accumulation from water to Daphnia magna: comparison of natural waters and standard preparations.

The bioaccumulation of benzo[a]pyrene (BaP) into Daphnia magna from two natural humic waters (one lake water and one bog water), and two humus preparations (Nordic Reference fulvic acid (Nordic FA) and a lyophilized concentrate) of the same aquatic origin was measured by using several dissolved organic carbon (DOC) concentrations for each sample. The partition coefficient (Kp) of BaP to the humus content of the water was determined by an equilibrium dialysis technique. In all four samples, an increase in humus concentration decreased the bioavailability of BaP in a logarithmic manner. The Nordic FA and the natural untreated humic water, from the same source as the water used for isolation of Nordic FA, gave a similar DOC bioaccumulation response and similar Kp values. The difference between the two natural humic waters was obvious, both in the accumulation experiments and the Kp values. The assumption that the total bound fraction of organic pollutant is not available for D. magna is not fully supported by this study.

Animals↗
PubMed1988

Deletion mapping of the beta-glucuronidase gene.

GUSB, the gene for beta-glucuronidase, has been localized to the proximal long arm of chromosome 7 between 7q11.2 and 7q22. Deficiency of beta-glucuronidase results in mucopolysaccharidosis type VII (MPS VII, Sly syndrome). The enzymatic defect has been demonstrated in cultured skin fibroblasts, leukocytes and serum of affected patients. An 8-yr-old boy presented with manifestations similar to MPS VII (mental retardation, short stature, "coarse" facial appearance, mild skeletal involvement and recurrent lower respiratory tract infection) but other, discrepant abnormalities, e.g., bilateral iris colobomata and cleft palate. Normal activity of beta-glucuronidase was found in the patient's leukocytes. Chromosome analysis disclosed an interstitial deletion of 7q with one breakpoint at the interface between bands 11.22 and 11.23 and the other breakpoint within band 21.1. DNA from this patient's leukocytes was analyzed for dosage of GUSB sequences. This locus appeared to be present at the normal diploid level. These findings suggest that GUSB is not in the portion of chromosome 7 deleted in our case, narrowing the smallest region of overlap to 7q21.1----7q22. We therefore assign the beta-glucuronidase gene to 7q21.1----7q22.

Child↗
PubMed1988

Access to primary health care in urban Iceland.

The accessibility by telephone of primary health care was studied in Reykjavik and its surrounding municipalities. Comparison was also made between community run health centres and private practices. About 60% of the total population of Iceland live within the study area. The study used medical secretaries as patient substitutes. During the prescribed telephone time, all "patients" were able to make telephone contact with their practice facilities, and 80% reached their doctor within 10 min. The waiting time for non-acute appointments was never more than three days. The study did not detect any difference in accessibility between community run health centres and privately owned GP practices.

Appointments and Schedules↗
PubMed1987

Pharmacokinetics of ciprofloxacin: intravenous and increasing oral doses.

The pharmacokinetics of ciprofloxacin, after administration of single oral doses of 100, 250, 500, and 1,000 mg, and an intravenous dose of 100 mg, were determined in 12 healthy volunteers (six women and six men). Serum concentrations were determined by high-pressure liquid chromatography, and urine samples were assayed microbiologically. The peak serum concentrations and the total areas under the serum concentration curves increased in proportion to the size of the oral dose. The pharmacokinetics of ciprofloxacin were described by a dose-independent linear relationship. The apparent oral bioavailability was 85 percent, based on comparison of the total areas under the serum concentration curves of the 100-mg dose. The serum concentrations during steady state were not significantly higher than after the first dose. The serum half-life ranged from 3.0 to 3.4 hours after the oral doses, and was 2.9 hours after the intravenous dose. The elimination-phase apparent distribution volume coefficient, delta d,area, was 2.76 liters/kg, and the total body clearance was 42.0 liters/hour. The 24-hour urinary excretion was 42.2 +/- 15.6 percent after the 100-mg intravenous dose and 42.5 +/- 17.6 percent after the 500-mg twice-daily oral dose during steady state.

Administration, Oral↗
PubMed1986

Pharmacokinetics of ciprofloxacin after intravenous and increasing oral doses.

The pharmacokinetics of ciprofloxacin were evaluated after increasing single oral doses of 100, 250, 500 and 1000 mg, and an intravenous dose of 100 mg given to each of 12 healthy volunteers (6 females and 6 males). Concentrations in serum and urine were determined by microbiological assay. The rise in peak serum concentrations and the values of the total area under the serum concentration curve were proportional to the increase in the oral doses. As the oral dose increased a slight increase was observed in the apparent time lag before absorption from 0.34 h after 100 mg to 0.53 h after 1000 mg. The serum half-life after the intravenous dose was 3.2 h. After the oral doses shorter apparent half-life values were observed. The intravenous dose showed an elimination phase distribution volume of 2.76 l/kg and total body clearance of 40.7 l/h. The total urinary excretion was 42.2 +/- 15.6% of the dose after the intravenous dose; the figure was lower after the oral doses. The bioavailability of the 100 mg oral dose was 83.7% as calculated from the value of the total area under the serum curve after the same oral and intravenous dose in all 12 subjects. Ciprofloxacin thus demonstrates normal linear pharmacokinetics, the rise in serum concentrations being proportional to the dose.

Administration, Oral↗
PubMed1981

Surgical treatment of acquired subglottic stenosis.

Seven patients with severe acquired glottic-subglottic stenosis were treated surgically, some of them by the augmentation principle and other by resection. The surgical results are reported and although only 50 per cent could be decannulated it was evident, at the end of a minimum follow-up period of 4 years, that the physical, mental, and social handicaps suffered by a child permanently wearing a cannula are so great that a very active surgical attitude to the problems of laryngeal stenosis is required.

Adolescent↗