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Biomedical subjects

W Hanke

Publications and source records attributed to W Hanke.

At least 145 records · Page 8Linked to original sources
PubMed1989

Corticosteroid receptors in liver cytosol of the clawed toad, Xenopus laevis: influence of thyroid and ovarian hormones.

The glucocorticoid receptor capacity Ro and the dissociation constant Kd were determined in the liver of Xenopus laevis by Scatchard analysis. In 5-year-old female toads Ro was about three times higher than that in males (153.9, 54.3 fmol/mg protein) and Kd was similar in both sexes (4.0, 4.1 nM). Some of the animals used had abnormal enlarged thyroid glands, atrophic ovaries, or both defects in connection with different levels of Ro, but not of Kd, compared to those of normal animals. Females with ovarian atrophy showed significantly lower Ro values, in the same range as in normal males, and a high liver weight. In male and female toads with enlarged thyroid glands and in animals with both defects a significantly higher Ro occurred compared to that of the corresponding group without this abnormality. To study the influence of thyroid hormones on glucocorticoid receptors, young toads (2-3 years old) received injections of 4-phenyl-2-thiouracil, T3, or T4 on 7 consecutive days. Ro and Kd were determined on the following day. Doses of 50 and 500 ng T3 and of 500 and 5000 ng T4 per gram of body weight and day resulted in an increase of Ro up to 250% of the controls. Injections of T3 were more efficient in males than in females. The effect of thyroxine was about the same in both sexes. These observations suggest that thyroid and ovarian hormones exert an influence on glucocorticoid receptor capacity and may belong to the factors which regulate glucocorticoid receptors.

Animals↗
PubMed1988

Corticosteroid receptors in liver cytosol of the clawed toad, Xenopus laevis: daily and seasonal variations.

In postmetamorphic Xenopus laevis liver cytosol the glucocorticoid binding capacity R0 and the dissociation constant Kd were determined. The receptor assay included an incubation period of 24 hr at 0-4 degrees with sodium molybdate to stabilize the receptor. Dexamethasone, triamcinolone acetonide, and corticosterone as tritiated ligands were compared regarding the R0 (67.6, 57.2, and 30.7 fmol/mg protein), the Kd (3.54, 0.56, and 9.03 nM), and the rate of dissociation in young specimens of X. laevis. In adult toads the [3H]dexamethasone receptor binding capacity was threefold higher in females than in males (153.86 +/- 12.19, 54.29 +/- 4.5 fmol/mg protein)--with about the same Kd (3.97 +/- 0.57, 4.08 +/- 0.28 nM). Young toads were kept under an artificial light regime (light from 600 to 1800 hr) and dexamethasone binding was measured every 3 hr. Unlike Kd, R0 showed a significant diurnal variation with maximal values at 600 and 1800 hr, which occurred about 9 hr after a maximal level of corticosterone in serum was reached (900, 2100). Seasonal variations of the [3H]dexamethasone and [3H]corticosterone binding capacity were different in both sexes of adult X. laevis. Maximal values in males were found in June/July and October/November. In females, the R0 was increased in the second half of the year with the maximum in August (275.5 +/- 45.02 fmol/mg protein). No correlation between R0 and the concentrations of corticosterone or aldosterone existed.

Aldosterone↗
PubMed1988

Long-term starvation in Xenopus laevis Daudin--II. Effects on several organs.

1. The effect of starvation for 12 months on organo-somatic indices, glycogen, protein and water contents of several organs and the Na+/K+ ratio in muscle was studied in the South African clawed toad Xenopus laevis Daudin. 2. The liver- and ovary-somatic index were reduced by 30 and 70% of the initial value after 12 months. Fat bodies had disappeared after approximately 6 months of starvation. The indices of heart and kidney were not changed. 3. Glycogen concentration of the liver, ovaries and muscle were depleted nearly totally during the first half of the experimental time, whereas glycogen in the kidney seemed to be unaffected. 4. Protein concentration increased in the liver, decreased in the muscle and remained constant in the kidney. 5. Starvation caused an increase of the water concentration of the whole animal and different organs, especially at the end of the experiment. 6. The Na+/K+ ratio of the muscle increased significantly after 6 months of starvation and reached a maximum after 10 months.

Animals↗
PubMed1988

cGMP-dependent channel protein from photoreceptor membranes: single-channel activity of the purified and reconstituted protein.

The cGMP-dependent channel protein has been purified from bovine rod photoreceptor membranes and incorporated into planar lipid membranes. At low divalent cation concentrations, cGMP stimulated single-channel current fluctuations. The probability Po of the channel being open strongly depended on the cGMP concentration (EC50 = 31 microM; Hill coefficient, n = 2.3); whereas the single-channel conductance (lambda = 26 pS) was independent of the agonist concentration. The agonist-stimulated increase in the probability of an open channel was largely due to shorter closed times and, to a lesser extent, due to the channel staying open for a longer time. The current-voltage relationship of the single open channel deviated from ohmic behavior, and the open probability decreased at more negative membrane potentials. The rectification of the macroscopic cGMP-induced current in artificial bilayers that contained many channel copies can be accounted for by the voltage dependence of channel gating together with the nonlinearity of the current-voltage curve of an open channel. Current fluctuations exhibited a variety of sublevels, indicating that the channel may exist in more than one conductive state.

Animals↗
PubMed1988

Electrical and biochemical properties of the cGMP-gated cation channel from rod photoreceptors.

The light-sensitive channel in the surface membrane of vertebrate photoreceptors is gated directly and cooperatively by cGMP, and the activation mechanism does not involve phosphorylation by a cGMP-dependent protein kinase. The channel protein most likely is composed of several copies of a single type of polypeptide, which can be removed from photoreceptor membranes by detergents and functionally reincorporated into the membrane of liposomes or planar bilayers. Most channel properties are preserved in the reconstituted system and provide a unique system to study the mechanisms of activation, regulation, and ion permeation in more detail.

Animals↗
PubMed1988

Pathogenic and non-pathogenic Entamoeba: pore formation and hemolytic activity.

Pore-forming activity in planar lipid bilayers and liposomes of extracts from differentially pathogenic Entamoeba and the capacity of trophozoites and subcellular fractions to lyse human red blood cells (hrbc) were investigated. In all amebas studied, the two activities paralleled each other. They were high in E. histolytica irrespective of the virulence of the particular strain, but low in non-pathogenic E. histolytica-like amebas of human origin as well as in E. invadens, which is pathogenic for reptiles, and in E. moshkovskii isolated from sewage. We conclude that the capacities to insert pores and to lyse are not sufficient for virulence although they may be necessary. The subcellular distribution of the hemolytic activity of E. histolytica and its sensitivity to a variety of inhibitors and activators differ from those of other known amebic cytotoxic activities including pore formation. Therefore, there may be an additional constituent of E. histolytica involved in the cytotoxicity of the parasite.

Animals↗
PubMed1987

Identification, purification, and functional reconstitution of the cyclic GMP-dependent channel from rod photoreceptors.

The cyclic GMP-dependent cation channel from bovine rod outer segments has been purified to greater than 90% homogeneity by a rapid two-step chromatographic procedure. The purified channel has an apparent molecular mass of 63 kDa as determined by NaDodSO4/gel electrophoresis. When incorporated into the membrane of liposomes, the purified protein mediates the cyclic GMP-dependent efflux of entrapped Ca2+. The reconstituted channel protein exhibits properties similar to the cyclic GMP-dependent channel observed in excised patches of the plasma membrane and in disk membranes. Cyclic GMP activated the channel cooperatively (Hill coefficient n = 3.1) with an apparent Michaelis constant of approximately 11 microM. After reconstitution of the purified protein into a planar lipid bilayer, we recorded cyclic GMP-stimulated single-channel activity. The single-channel conductance at physiological salt concentrations and in the absence of divalent cations was 26 pS. The drug l-cis-diltiazem, shown to block the cyclic GMP-dependent channel in excised patches of the plasma membrane and in isolated disks of rod outer segments, was ineffective against the purified channel.

Animals↗
PubMed1987

Characterization of the channel properties of a neuronal acetylcholine receptor reconstituted into planar lipid bilayers.

An alpha-toxin-binding membrane protein, isolated from the head and thoracic ganglia of the locus (Locusta migratoria), was reconstituted into planar lipid bilayers. Cholinergic agonists such as acetylcholine, carbamylcholine, and suberyldicholine induced fluctuations of single channels, which suggests that the protein represents a functional cholinergic receptor channel. The antagonist d-tubocurarine blocked the activation of the channels, whereas hexamethonium had only a weak effect; similar properties have been described for nicotinic insect receptors in situ. The channel was selectively permeable to monovalent cations but was impermeable to anions. The conductance of the channel (75 pS in 100 mM NaCl) was independent of the type of agonist used to activate the receptor. Kinetic analysis of the channel gating revealed that, at high agonist concentrations (50 microM carbamylcholine), more than one closed state exists and that multiple gating events, bursting as well as fast flickering, appeared. At very high agonist concentrations (500 microM carbamylcholine), desensitization was observed. Channel kinetics were dependent on the transmembrane potential. Comparing the conductance, the kinetics, and the pharmacology of nicotinic acetylcholine receptor from insect ganglia and fish electroplax reconstituted into bilayers revealed obvious similarities but also significant differences.

Animals↗
PubMed1986

The distribution of interrenal stimulating activity in the brain of Xenopus laevis.

The stimulation of corticosteroid release by the interrenal tissue of Xenopus laevis was investigated using an in vitro preparation of the interrenals and a radioimmunoassay for determinations of corticosterone and aldosterone in the perifusate. The stimulatory activity of four different areas was tested, the pars distalis, the post- and preoptic hypothalamus, and the cerebrum. It was found that besides the pars distalis, the post- and preoptic hypothalamus exhibit stimulatory activity on the interrenals. No such activity was found in the cerebrum. There was a decrease of activity found from the pars distalis to the postoptic and then to the preoptic part of the hypothalamus. The release of both steroids had different sensitivity. Aldosterone release was significantly elevated by all three different tissues, while the increase of the release of corticosterone was only found significant in the case of stimulation by the pars distalis. The results also make clear that the increase of the release of corticosterone is less than that of aldosterone. The ratio of corticosterone to aldosterone decreased significantly after stimulation. This points to the fact that the rate of conversion of corticosterone to aldosterone (18-hydroxylation) is stimulated more than the production of corticosterone from progesterone.

Adrenal Cortex Hormones↗
PubMed1986

Circadian rhythm of interrenal activity in Xenopus laevis.

Young specimens of Xenopus laevis were kept under constant environmental conditions (artifical light from 600 to 1800 hr, feeding between 800 and 900 hr) and the concentrations of aldosterone and corticosterone in the serum were measured every 3 hr. Furthermore, the kidneys containing the interrenals were removed and their corticosteroid release under stimulation by the pars distalis and mammalian ACTH was determined. Under these conditions, the corticosteroid levels in the serum were maximal from 900 to 1200 hr (corticosterone, 7.7 +/- 0.47 ng/ml; aldosterone, 2.8 +/- 0.27 ng/ml) and minimal during the night (corticosterone, 5.2 +/- 0.43 ng/ml; aldosterone, 1.7 +/- 0.18 ng/ml). The basal secretion rate of the interrenals in vitro showed the opposite course (corticosterone, 24 +/- 3 to 72 +/- 8 pg/min/tissue; aldosterone, 46 +/- 5 to 68 +/- 9 pg/min/tissue). Stimulation by the pars distalis and mammalian ACTH clearly increased the secretion rate. After both types of stimulation the original rhythm was lost for aldosterone but still present for corticosterone. The ratio of the amounts of corticosterone/aldosterone was greater than 1.0 in the serum but less than 1.0 in the incubation fluid. It decreased significantly after stimulation in vitro by pars distalis or ACTH.

Adrenal Glands↗
PubMed1985

A comparison of physiological changes in carp, Cyprinus carpio, induced by several pollutants at sublethal concentrations. I. The dependency on exposure time.

Carp were exposed to 10 different pollutants at sublethal concentrations for 6, 24, or 72 hr. Blood, liver, and white muscle samples were taken after the exposure time together with samples of control handled fish. Serum concentrations of glucose, cortisol protein, and cholesterol were determined. Similarly, the liver and muscle glycogen contents were measured. The effects of the following pollutants were examined: aldrin (100 micrograms/liter), atrazine (100 micrograms/liter), DDT (50 micrograms/liter), dieldrin (20 micrograms/liter), endrin (2 micrograms/liter), hexachlorbenzene (100 micrograms/liter), lindane (100 micrograms/liter), methanol (1 ml/liter), 4-N-phenol (100 micrograms/liter), toluene (100 microliters/liter). The rises in serum glucose and cortisol were the most frequent changes occurring after exposure to the pollutants. A decline in plasma protein and cholesterol content was also often observed. Liver glycogen concentration increased first in most cases and was reduced after longer exposure. Muscle glycogen was affected differently, sometimes reduced by exposure to the pollutants. The experimental design allows for the gradual increase in toxicity of the pollutants used regarding the applied concentrations. Furthermore, the aim of the paper is to evaluate the tests for proof of toxicity of those chemicals. The determination of serum glucose and cortisol levels can be proposed as mostly useful. The clearest changes in all parameters were found after treatment with 100 micrograms/liter atrazine and 50 micrograms/liter DDT. When serum glucose and cortisol concentrations were quickly elevated, signs for exhaustion could be seen after 72 hr of exposure.

Animals↗
PubMed1985

Accumulation of pollutants in fish.

The amount of radioactivity which derived from 14C-labeled pollutants was determined in liver, kidney, intestine, blood, muscle and gills of carp, exposed for 6, 24 and 72 hr to high external concentrations of urea, methanol, atrazine and PCP. The results allowed one to calculate roughly the uptake rate for these compounds. It was low for urea (0.055 micrograms/g per hr), higher for methanol (0.12) and atrazine (0.16) and highest for PCP (1.5). The bioaccumulation factors (BFs) were determined for the different substances and organs. They correlated with the hydrophilic-lipophilic nature of the chemicals. The more lipophilic the substances the more accumulation occurred in the liver. PCP accumulated the most. BF was 300-400 in most tissues except muscle where it was quite low. The BF was 3-4 for atrazine in liver, kidney and intestine, but just 1 in blood, muscle and gills. There is some evidence that the BF for methanol equals 1 in liver, kidney, gills and intestine. It is less than 1 in blood and muscle. Urea was equally distributed in all organs and in the external medium.

Animals↗