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Biomedical subjects

M Höfer

Publications and source records attributed to M Höfer.

At least 73 records · Page 4Linked to original sources
PubMed1987

[Aspergillosis following liver transplantation as a hospital infection].

In the first four weeks after a liver transplantation, there was an invasive aspergillosis with a lethal course in three out of five patients who were treated postoperatively in the same room. The clinical symptoms were very different. One patient was asymptomatic, and the diagnosis could only be made by autopsy. In another patient, pulmonary symptoms, and in the third patient, cerebral symptoms were the most prominent. In the two latter patients, the infection was demonstrated in the sputum and by bronchoalveolar lavage. The disease course was fulminant in all patients, and therapy was without success. Owing to this high incidence, mycological investigations were carried out on the ward. A flower bench in the hall beside the ward was probably the main focus of distribution. To avoid such nosocomial infections, foci of aspergillus distribution should if possible be removed from the surroundings of patients with weakened immune resistance.

Adult↗
PubMed1987

[Problems in the reconstruction of bile flow in orthotopic liver transplantation].

In hepatic transplantation complications of the biliary drainage were frequently observed. Ischemia of the extrahepatic bile duct which occurs for anatomical reasons can cause necrosis of the bile duct. The reconstruction of biliary drainage by biliodigestive anastomosis results in ascending infections of the graft. Biliary sludge could obstruct the intra- or extrahepatic bile duct. Recently, operation methods are mainly applied in which the function of Oddi's sphincter is preserved, i.e. choledocho-choledochostomy or gallbladder conduit method. If it is not possible to perform these methods the Roux-y-jejunum loop is used. Finally, an immediate operative revision of the biliary drainage is indicated if its complication is diagnosed.

Bile Ducts↗
PubMed1987

Alteration of thymus and of immune regulatory-antifibroblast factors in acute and chronic hepatic damage.

We studied in this paper the behavior of immunosuppressive and fibroblast proliferation inhibitory factors in the acute, chronic damage and cirrhotic alteration of the liver. We induced in LEW-rats acute hepatic necrosis by i.v. application of dimethylnitrosamine (DMNA: 35 mg/kg b.wt.) and by i.m. injection of CCl4 (1 ml/kg b.wt., twice a week). After 2-4 weeks we found chronic hepatic damage and after 8-10 weeks liver cirrhosis. As a control, untreated animals were used. Sera and liver factors were prepared from the animals and used for inhibition tests of fibroblast proliferation and MLC reaction. Furthermore, cell count and cell subpopulation of the thymus were determined by monoclonal antibodies (W3/25, OX-8). LF of untreated and DMNA-treated animals exhibited very strong unspecific inhibition effects of fibroblast proliferation and allogenic stimulation. However, with progression of hepatic damage (chronic hepatitis and cirrhosis) both suppressive abilities were gradually reduced. Normal sera showed very slight inhibition of allogenic stimulation but sera of animals with acute hepatic damage showed very strong inhibition. In the 2 weeks of CCl4 treatment, their inhibitory abilities were more than 40%, and with progression of hepatic damage they were gradually reduced. Normal sera or sera of animals with chronic hepatic damage could not suppress the fibroblast proliferation; however, sera of acute hepatic damage inhibited it very strongly. With chronic hepatic damage, the thymus gradually atrophied and, after 10 weeks of CCl4 treatment, it had atrophied completely. Thymocyte differentiation was found only in animals with acute hepatic damage. This suggests that factors which were liberated from the damaged hepatocytes caused differentiation of the thymocytes.

Acute Disease↗
PubMed1987

Thymus alteration in hepatic regeneration.

We performed 70% hepatectomy in LEW rats and examined immunologic alterations during hepatic regeneration; especially, thymus weight and cell count, T-cell subpopulations, differentiation ratio of thymocytes (DR) and ratio of T-helper to T-suppressor/cytotoxic cells (Th-Tsc). Strongest liver regeneration was observed on postoperative days 2-5 and it was completed on day 7. During hepatic regeneration a significant thymus atrophy in weight and cell count was found on day 3 and 5, it normalized from the 7th day on. T-cells were highly differentiated during liver regeneration with a DR of 35.7 +/- 2.5%, 64.0 +/- 4.4% and 38.8 +/- 3.0% on postoperative days 3, 5, and 7, respectively, and at the same time Th-Tsc ratio was reduced to 0.57 +/- 0.11, 0.38 +/- 0.04 and 0.57 +/- 0.05, respectively. DR and Th-Tsc ratio showed a trend to normalization from the 7th day on. No changes of thymus and T-cell subpopulations occurred in a sham-operated control group. Since we found such thymus alterations also in spontaneous or drug induced tolerant graft recipients, we conclude that the hepatic regenerative potential possesses a suppressive effect on immune responses.

Animals↗
PubMed1987

The electrochemical gradient of H+ in Candida albicans and its relevance to the uptake of nutrients.

The electrochemical gradient of protons, delta microH+, in Candida albicans was estimated between pH 3.5 and 8.5. The electrical potential difference (delta psi) and the chemical proton gradient (delta pH) were measured by steady-state distribution of tetraphenylphosphonium ion and of propionic acid across the plasma-membrane, respectively. In the pH range tested, the intracellular pH was maintained fairly constant at values between 7.3 and 8.1. On the other hand, there was an up to three fold enhancement of delta psi under similar conditions. The uptake of a neutral (glycine), an acidic (L-glutamate) and a basic (L-arginine) amino-acids and of the aldopentose (D-xylose) was determined under different values of delta microH+, which was manipulated by varying the pH of the cell suspension. The rate of uptake of D-xylose and glycine appeared to follow delta microH+ while the uptake velocity of L-arginine could be correlated to changes in delta psi. The rate of uptake of L-glutamate, although at highest among the rates of tested nutrients, was, however, largely independent of delta microH+. This and other reasons (discussed below) indicate that delta microH+ may not be the sole driving force of nutrients uptake in C. albicans.

Biological Transport↗
PubMed1987

Relevance of cation-exchange capacity of cell wall in detecting H+-symport in yeasts.

Addition of mono- or divalent cations to unbuffered yeast suspensions causes acidification of the medium. In some yeasts (Rhodotorula glutinis and Metschnikowia reukaufii) this represented a mediated H+ extrusion in exchange for cations (mostly K+). However, in some other yeasts (Pichia humboldtii and Candida albicans) the pH change was very rapid. The rapid acidification of the media by Pichia humboldtii was found to be due to high cation-exchange capacity of its cell wall. This cation-exchange was saturable, exhibited high affinity for divalent cations and was stoichiometric under appropriate experimental conditions. Results suggest that such cation exchange capacity of some yeasts could hamper the measurements related to H+-symport mechanisms.

Cell Wall↗
PubMed1986

Tetraphenylphosphonium is an indicator of negative membrane potential in Candida albicans.

The characteristics of the uptake of lipophilic cations tetraphenylphosphonium (TPP+) into Candida albicans have been investigated to establish whether TPP+ can be used as a membrane potential probe for this yeast. A membrane potential (delta psi, negative inside) across the plasma membrane of C. albicans was indicated by the intracellular accumulation of TPP+. The steady-state distribution of TPP+ was reached within 60 min and varied according to the expected changes of delta psi. Agents known to depolarize membrane potential caused a rapid and complete efflux of accumulated TPP+. The initial influx of TPP+ was linear over a wide range of TPP+ concentrations (2.5-600 microM), indicating a non mediated uptake. Thus, TPP+ is a suitable delta psi probe for this yeast.

Biological Transport↗
PubMed1985

Tetraphenylphosphonium ion is a true indicator of negative plasma-membrane potential in the yeast Rhodotorula glutinis. Experiments under osmotic stress and at low external pH values.

In the yeast Rhodotorula glutinis, accumulation of the tetraphenylphosphonium ion (TPP+) was increased under conditions of osmotic stress, indicating a hyperpolarization of the negative membrane potential (delta psi). The following observations were consistent with the occurrence of hyperpolarized delta psi: enhanced accumulation of glucosamine, the uptake of which is also driven by delta psi; increased respiratory rate. The accumulation of TPP+ was gradually decreased by lowering the pH of cell suspensions. At pH values below 4.5, no TPP+ was taken up, but instead thiocyanate (SCN-) was accumulated, indicating a positive delta psi. The pH-dependent influx of glucosamine followed the pattern of TPP+ accumulation both in the wild-type and in the nystatin-resistant mutant, M67, which displayed a negative delta psi down to pH 3. Thus TPP+ accumulation in Rh. glutinis reflected actual electrical potential difference across the plasma membrane.

Glucosamine↗
PubMed1985

The electrochemical H+ gradient in the yeast Rhodotorula glutinis.

The electrochemical gradient of protons, delta mu H+, was estimated in the obligatory aerobic yeast Rhodotorula glutinis in the pH0 range from 3 to 8.5. The membrane potential, delta psi, was measured by steady-state distribution of the hydrophobic ions, tetraphenylphosphonium (TPP+) for negative delta psi above pH0 4.5, and thiocyanate (SCN-) for positive delta psi below pH0 4.5. The chemical gradient of H+ was determined by measuring the chemical shift of intracellular Pi by 31P-NMR at given pH0 values. The values of pHi increased almost linearly from 7.3 at pH0 3 to 7.8 at pH0 8.5. In the physiological pH0 range from 3.5 to 6, delta mu H+ was fairly constant at values between 17-18 KJ mol-1, gradually decreasing at pH0 above 6. In deenergized cells, the intracellular pHi decreased to values as low as 6, regardless of whether the cell suspension was buffered at pH0 4.5 or 7.5. There was no membrane potential detectable in deenergized cells.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1983

Passive fluxes of K+ and H+ in wild strain and nystatin-resistant mutant of Rhodotorula gracilis (ATCC 26194).

The passive fluxes of protons and potassium ions have been studied in the obligatory aerobic yeast Rhodotorula gracilis. The cellular energy metabolism was suspended by introducing anaerobic conditions. The H+-permeability of the plasma membrane was modified by adding an uncoupler under both aerobic and anaerobic conditions. Unfortunately, the plasma membrane of R. gracilis was insensitive to K+-ionophores. The passive flows of H+ and K+ under anaerobic and/or uncoupled conditions were electrically coupled and exhibited a constant stoicheiometry of 1:1. The H+ permeability of the plasmalemma was shown to determine the velocity of the passive K+-H+ exchange. The nystatin-resistant mutant M 67 displayed distinctly lower permeability for both H+ and K+, which can explain the observed differences in some transport characteristics of the two strains. In order to account for the properties of passive K+ flows, a membrane-potential-gated channel for K+ has been proposed. Evidence is presented that the inhibitor of the plasmalemma-bound H+-ATPase, N,N'-dicyclohexylcarbodiimide (DCCD), reduced at first the permeability for both K+ and H+ and only upon prolonged incubation the ATPase itself. Since DCCD effected an immediate hyperpolarization of the membrane potential, it has been concluded that the H+ does not slip through the H+-ATPase under deenergized conditions.

Anaerobiosis↗
PubMed1983

Membrane potential and cation permeability. A study with a nystatin-resistant mutant of Rhodotorula gracilis (Rhodosporidium toruloides).

Cells of a nystatin-resistant mutant of the obligatory aerobic yeast Rhodotorula gracilis displayed an electrical potential difference, delta psi, across the plasma membrane which was, in contrast to the wild-strain cells, virtually independent of the pH of cell suspensions down to 4.5. In addition, the delta psi in mutant cells was insensitive to extracellular K+ concentrations. The mutant cells failed to cotransport measurable amounts of H+ by the onset of monosaccharide transport and to take up K+ in exchange for H+. Taking into account the lower passive permeability of the mutant plasma membrane for cations, it has been concluded that the pH dependency of delta psi in wild-strain cells is correlated with the electrogenic leak of H+ back into the cells in course of increasing delta pH across the plasma membrane.

Cell Membrane↗
PubMed1982

Variable H+/substrate stoicheiometries in Rhodotorula gracilis are caused by a pH-dependent protonation of the carrier(s).

Two carrier-mediated systems transport sugars in the yeast Rhodotorula gracilis depending on the pH. One system, with higher affinity for sugars, catalyses a symport of protons with sugar, whereas the other system, having lower affinity, is independent of protons. This was shown in three different ways. (1) At low pH, where only the high-affinity system works, a H+/sugar stoicheiometry of 1 was found. An increase of the pH and of the sugar concentration, which allowed the low-affinity system to operate, brought about a drop of the stoicheiometry to values below 1. (2) During H+ symport the influx of positive charge was electrically compensated by an equivalent efflux of K+ from the cells. At high pH and high sugar concentrations this stoicheiometry of K+ and sugar decreased concomitant with the H+/sugar stoicheiometry. (3) At pH 7.5 both transport systems were operating, as shown by biphasic saturation kinetics. Under these conditions only the high-affinity transport was found to be electrogenic. These results agree with the theory of an electrogenic H+/sugar symport where changes in the affinity for substrate are brought about by reversible protonation and deprotonation of the carrier.

Biological Transport↗
PubMed1982

A nystatin-resistant mutant of Rhodotorula gracilis. Transport properties and sterol content.

A nystatin-resistant mutant of Rhodotorula gracilis was obtained by treatment of the wild strain cells with N-methyl-N-nitro-N-nitrosoguanidine and selected on agar plates containing 150 micrograms nystatin/ml. Three important transport functions of the plasma membrane of mutant cells: the accumulation of monosaccharides, the generation and maintenance of the pH-gradient and of the membrane potential, as well as the cell respiration were insensitive to at least 10(-5) M nystatin. This concentration of nystatin inhibited completely all these processes in wild strain cells. Analysis of cellular sterols revealed a defect of ergosterol biosynthesis in the mutant, which was localized at the last oxidative step between 5,6-dihydroergosterol and ergosterol.

Biological Transport↗
PubMed1981

Active transport of charged substrates by a proton/sugar co-transport system. Amino-sugar uptake in the yeast Rhodotorula gracilis.

1. In the yeast Rhodotorula gracilis several amino sugars were actively transported. Glucosamine, which is largely protonated at physiological pH (pK 7.75) was used as a model substrate. At pH 6.75 its half-saturation constant was 1 mM and the maximal velocity was 50 nmol/min per mg dry wt. 2. Amino sugars were taken up via the monosaccharide carrier. The transport of glucosamine was strongly restricted by monosaccharides. D-Xylose inhibited competitively the uptake of glucosamine. The inhibition constant was 1 mM. Cells preloaded with D-xylose showed exchange transport on subsequent addition of glucosamine. 3. Transport of glucosamine was energized by the membrane potential. Uncoupling agents such as carbonyl cyanide m-chlorophenyl-hydrazone and the lipophilic cation TPP+ (tetraphenylphosphonium ion) at concentrations that depolarized the membrane potential inhibited the uptake of glucosamine. Conversely the transport of glucosamine partly dissipated the membrane potential, which was monitored by radioactively labelled lipophilic cations. 4. The translocated charges were electrically compensated by the extrusion of protons and K+ (1 glucosamine molecule/0.85 H+ + 0.15 K+). 5. An increase of the pH in the range 4.75-8.75 lead to a decrease of the half-saturation constant from 5 mM to 1 mM and to an optimum of the maximal velocity at pH 6.75. We suggest that this fair constancy is due to the carrier not distinguishing between the protonated form of glucosamine (pH less than 7.75) and the deprotonated form (pH greater than 7.75). The increase of V(T) (maximal transport velocity) between pH 4.75 and 6.75 is due to the increase of the membrane potential: the decrease between pH 6.75 and 8.75 is due to the deprotonization of the carrier.

Amino Sugars↗