Biomedical subjects

J Wensink

Publications and source records attributed to J Wensink.

11 recordsLinked to original sources

PubMed1990

Hearing loss related to zinc deficiency in rats.

Based on the observation that the zinc concentration in the cochlea of guinea pigs is very high, Shambaugh in North America has suggested that zinc plays an important role in hearing. Zinc deficiency is not infrequently present in growing children and elderly people, and thus might result in a hearing loss, which should be treated with zinc supplementation. The present experiment examined the effects of a zinc-deficient diet on hearing in 7-week-old rats. The auditory brainstem response threshold was measured in four rats before, during and after a zinc-deficient diet. Concentrations of zinc in the brain and in several other organs were measured, and the cochleas were examined microscopically. No hearing loss or morphological change in the cochlea of these animals was detected, although a clear zinc-deficient status was reached.

Animals↗

PubMed1989

Dietary zinc deficiency has no effect on auditory brainstem responses in the rat.

Zinc has been shown to effect--in vitro--a number of processes associated with neurotransmission. We have tested whether the rate of impulse conduction--in vivo--as measured from the latencies of auditory brainstem responses (ABR), is influenced by dietary zinc deficiency in the rat. Dietary zinc deficiency for up to 26 wk had no effect on the wave I-IV interval compared to zinc-adequate fed animals. The results are discussed in relation to the observed constancy of brain overall and extracellular fluid zinc concentrations under conditions of dietary zinc deficiency.

Animals↗

PubMed1988

Effect of excess dietary histidine on rate of turnover of 65Zn in brain of rat.

The effect of the chronic administration of histidine on the brain zinc level was examined in growing, male Wistar rats. Using a purified diet, the minimum zinc requirement for normal growth and normal plasma and tissue zinc levels was found to be around 10 ppm. Given this zinc content, the diet was supplemented with 5% and 8% histidine, respectively, or with 10% glycine (as control). Brain zinc was analyzed by measuring the rate of turnover of 65Zn from 2-4 weeks after a single injection of the tracer. Feeding the diet supplemented with 5% histidine caused a small decrease in the plasma zinc concentration and a slight increase in the rate of turnover of 65Zn in the cerebrum and the cerebellum as compared to the control group. The animals fed the diet supplemented with 8% histidine became severely zinc deficient (as evidenced by a 50% reduction in the plasma zinc content), however, the rate of turnover of 65Zn in all brain regions examined was significantly decreased as compared to the control group. The results indicate that histidine has no specific complexing action on the brain zinc.

Animals↗

PubMed1988

Zinc uptake into synaptosomes.

Zinc uptake was studied in synaptosomes, isolated by the Ficoll flotation technique, using the radiotracer 65Zn. True uptake of zinc could be discriminated from binding to the outside of the synaptosomes by the absence of accumulation at 0 degree C and the dependency of the rate of uptake on the medium osmolarity. The zinc uptake, studied in the presence of various zinc-complexing agents, showed saturation kinetics when analyzed in terms of [Zn]free, yielding Km = 0.25 microM. The zinc uptake was independent of both ATP and the Na+ gradient. No efflux of zinc could be demonstrated from preloaded synaptosomes due to the formation of insoluble zinc complexes inside the synaptosomes. The results are discussed in terms of the modulation of diverse neurochemical processes by zinc.

Adenosine Triphosphate↗

PubMed1987

The effect of dietary zinc deficiency on the mossy fiber zinc content of the rat hippocampus. A microbeam PIXE study. Particle Induced X-Ray Emission.

The effect of dietary zinc deficiency on the mossy fiber zinc content of the rat hippocampus was investigated using PIXE (Particle Induced X-Ray Emission) spectroscopy. Using the proton microbeam (60 X 60 microns), 2 mm line-scans were made on hippocampal sections and the data were expressed as absolute zinc concentrations. Values of 55 and 136 ppm (dry weight) were found for the mean background zinc level and the maximum mossy fiber zinc level, respectively, in animals fed a control diet containing 50 ppm zinc. Treatment of these animals with dithizone caused about 50% reduction in the maximum mossy fiber zinc level. Feeding a zinc-deficient diet for 28 days did not cause a decrease in the mossy fiber zinc level, however, feeding the zinc-deficient diet for 90 days reduced the maximum mossy fiber zinc level by about 30%. The results are discussed in relation to the behavioral abnormalities that have been observed in zinc-deficient animals.

Animals↗

PubMed1982

Attachment of lipoprotein to the murein of Escherichia coli.

The rate of incorporation of [3H]diaminopimelate into the lipoprotein attachment sites was compared to the rate of its incorporation into total acid-insoluble and dodecylsulphate-insoluble murein. In contrast to earlier findings, we could detect no significant difference in these rates of incorporation, suggesting that the lipoprotein molecules are not specifically excluded from the murein growth sites. The amount of lipoproteins bound to the murein increased when the cells entered the stationary phase of growth.

Bacterial Proteins↗

PubMed1981

Outer-membrane vesicles released by normally growing Escherichia coli contain very little lipoprotein.

The lipoprotein content of the outer-membrane medium vesicles, which are released from Escherichia coli during normal growth, was compared to the lipoprotein content of the corresponding cellular outer membranes. It was found that the medium vesicles contained only 35% free lipoprotein and almost none of the bound lipoprotein when compared with cellular outer membranes. Medium vesicles also had reduced amounts of protein II and a protein V (Mr = 16 000), while they contained large amounts of pore-forming proteins I and lamB. A mechanism is proposed in which outer membrane vesicles are formed when the outer membrane expands faster than the underlying peptidoglycan layer. The lack or enrichment of individual proteins in medium vesicles may be determined by their interactions with the peptidoglycan-bound lipoprotein complex.

Cell Membrane↗

PubMed1981

Identification of different forms of the murein-bound lipoprotein found in isolated outer membranes of Escherichia coli.

The identification of the free and murein-bound forms of the Escherichia coli lipoprotein on dodecylsulphate-polyacrylamide gels was systematically investigated by analyzing the low-molecular-weight proteins (Mr less than 20 000) of both cytoplasmic and outer membranes. The free form of the lipoprotein was identified on 15% polyacrylamide gels as the fastest migrating component (Mr = 7200-7500) of isolated outer membranes; it could be separated from a small cytoplasmic membrane protein (Mr = 6500) which was probably identical to the dicyclohexylcarbodiimide binding proteolipid of the membrane-bound ATPase. Lysozyme treatment of both outer membranes and murein sacculi failed to convert the murein-bound lipoprotein into a fragment of uniform size; instead the bound form appeared as a series of bands consisting of lipoprotein bound to one, two,...eight murein subunits. The composition of this ladder depended on the method used to isolate outer membranes. Beside these lipoprotein bands the outer membrane contained two other proteins, III and V; the relation of these proteins to previously described proteins is discussed.

Bacterial Proteins↗

PubMed1981

Conversion of free lipoprotein to the murein-bound form.

The time-course of the conversion of free lipoprotein to the murein-bound form was followed after pulsing growing cells of Escherichia coli for 2 min with [35S]methionine. The conversion of the free to the bound form was measured by two independent methods. First, the appearance of murein-bound lipoprotein was determined in isolated murein sacculi after extraction with hot 4% sodium dodecylsulphate. Second, the ratio of various forms of the bound lipoprotein to the free lipoprotein was determined in outer membranes. Both methods indicated that the half-maximal amount of bound lipoprotein was reached within one-sixth of a generation time.

Cell Membrane↗

PubMed1980

Some characteristics of the outer membrane material released by growing enterotoxigenic Escherichia coli.

The high-molecular-weight material released into the medium by Escherichia coli AP1, an enterotoxigenic strain of porcine origin, has been isolated and resolved into two clearly distinct fractions, based on sucrose density gradient and differential centrifugation, chemical analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and freeze-fracture electron microscopy. These two fractions, referred to as "medium vesicles" and "medium lipopolysaccharides", were compared with the cellular outer and cytoplasmic membranes, the periplasmic fraction, and the cytoplasmic fraction. The medium vesicles closely resembled outer membrane and accounted for 3 to 5% of the total cellular outer membrane. They contained most of the heat-labile enterotoxin (LT) activity released into the medium by E. coli AP1. The medium lipopolysaccharide consisted mostly of lipopolysaccharide and a small amount of outer membrane and contained relatively little LT activity. Based on experiments with E. coli K-12 strains, in which about 5% of the newly synthesized outer membrane is lost from areas of outer membrane synthesis, it is proposed that enterotoxigenic E. coli strains release LT as part of such newly synthesized outer membrane fragments and that released outer membrane fragments may function as physiologically significant LT carriers.

Centrifugation, Density Gradient↗

PubMed1978

Isolation of the membranes of an enterotoxigenic strain of Escherichia coli and distribution of enterotoxin activity in different subcellular fractions.

The intracellular localization of enterotoxin in Escherichia coli AP1, a strain of porcine origin which produces high levels of heat-labile, but no heat-stable enterotoxin, has been examined. The cytoplasmic and outer membranes of this strain both contained enterotoxin activity, while the membranes isolated from a serologically related non-enterotoxigenic strain (E. coli AP2) also of porcine origin, did not show enterotoxin activity. The periplasmic fraction isolated from the enterotoxigenic strain contained considerable enterotoxin activity, but this activity was associated with outer membrane fragments present in the periplasmic fraction. Thus, of the total cellular enterotoxin activity, about 55%, 15% and 30% were present in the outer membrane, cytoplasmic membrane and the cell cytoplasm, respectively. The specific activity of enterotoxin was 20 units per mg protein in the cytoplasm and 90 and 150 units per mg protein in the cytoplasmic and outer membranes, respectively.

Biological Assay↗