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Biomedical subjects

R Kroker

Publications and source records attributed to R Kroker.

32 records · Page 2Linked to original sources
PubMed1976

Leucocidin from Pseudomonas aeruginosa and membrane functions.

Leucocidin from Pseudomonas aeruginosa (strain 158) induced loss of potassium from isolated hepatocytes. The (Na+-K+) stimulated ATPase activity of isolated rat liver plasma membranes showed dose-dependent activation up to 56%. Electron-spin-resonance (ESR) measurements gave no indication of toxin-induced changes in membrane fluidity. On isolated guinea pig heart auricles the toxin produced an increase in frequency from 180/min to about 300/min, with arrhythmia and transitory flutter. On isolated nerve-diaphragm preparations the toxin caused a contracture and a decline in twitch tension, with a loss of potassium into the bathing solution. The action potential of the electrically stimulated N. ischiadicus of rat or frog was not affected when leucocidin was added to the bathing solution up to a concentration of 10 micrograms/ml.

Action Potentials↗
PubMed1976

Cholic acid uptake and isolated rat hepatocytes.

Cholic acid uptake was studied in isolated rat hepatocytes using a centrifugal filtration technique to allow rapid sampling. Hepatocytes were found to adsorb as well as to transport cholic acid. The adsorption was characterized by a capacity of 24 nmol X mg cell protein-1 and an association constant of 0.59 X 103 M-1. Cholic acid uptake was linear with respect to concentration at or below 10 degree C, suggesting a unsaturable uptake process which was considered to represent simple diffusion and is quantitated by a diffusion coefficient of 1.76 pmol cholic acid X min-1 X mg protein-1 X muM-1. Above 10 degrees C the uptake curve was biphasic. After subtracting the unsaturable component from uptake rates at higher temperatures, a curve showing saturable kinetics resulted. The apparent Km and V values at 37 degrees C were calculated to be 31muM and 0.8 nmol X min-1 X mg protein-1 respectively. This saturable uptake process was temperature-dependent with an activation energy of 13 kcal X mol-1 (5.44 X 104 J X mol-1) and was inhibited by oligomycin and KCN. Countertransport was demonstrated with cholic, taurocholic and chenodeoxycholic acids. The results suggest that cholic acid is transported by an energy-dependent carrier-mediated process in addition to simple diffusion by hepatocytes, and that the postulated carrier has affinity for other bile acids.

Adsorption↗
PubMed1975

Effects of concanavalin A on the isolated perfused rat liver.

In the isolated perfused liver, Concanavalin A provoked a significant decrease of flow rate within 2 to 4 min. which was dose-dependent and could be partly inhibited by specific antagonists. Furthermore it was found that the lectin led to a decline of the respiration, an increase of the lactate/pyruvate ratio and a release of the transaminases into the medium. It was suggested that Concanavalin A displaced endothelial cells in the liver capillaries, which occluded the vessels and decreased the flow rate. The decreased respiration was considered to be secondary to this effect.

Animals↗
PubMed1975

[Phalloidine antagonists. 1. Effects of silybine derivatives on isolated perfused rat liver].

The protective effect of two silybin derivatives against phalloidin was tested in isolated rat livers, perfused with an erythrocyte free medium. Both liver swelling and potassium loss were examined for the evaluation of antagonism. Liver swelling and potassium loss were markedly decreased when silybin hemisuccinate was added to the perfusion medium before the application of phalloidin. In contrast, the protective effect of this compound was minimal after the mushroom toxin was partially absorbed by the liver. The protective efficiency of a dimer derivative (disilybin) was much greater than that of the monomer product. The binding of both derivatives in the liver cannot be very strong because the protective effect mainly could be washed out by a single change of the perfusion medium. Spectroscopical studies on isolated hepatocytes indicate that silybin inhibits the interaction of phalloidin with the cell surface.

Absorption↗
PubMedDate not supplied

Confirmation of chloramphenicol residues in egg by gas chromatography/high-resolution mass spectrometry and comparison of quantitation with gas chromatography-electron capture detection.

Determination of chloramphenicol (CAP) residues in egg by gas chromatography/high-resolution mass spectrometry (GC/HRMS) with negative chemical ionization and gas chromatography with electron capture detection (GC-ECD) is described. A cleanup based on acetonitrile extraction followed by solid-phase extraction with silica gel and gel filtration columns was developed for extraction of CAP residues from whole egg. For quantitation, the internal standards used were the meta isomer of CAP (m-CAP) for GC-ECD and both m-CAP and deuterium-labeled CAP (D5-CAP) for GC/HRMS. For GC/HRMS, evaluation was performed by selecting characteristic ions at m/z 466 for CAP and m-CAP and at m/z 471 for D5-CAP. Both methods were validated with egg samples fortified at 0.4-2.0 micrograms/kg and lyophilized egg samples from animals treated at the 1 microgram/kg concentration level. The coefficient of variation was below 10%. Limits of detection and quantitation of both methods were about 0.3 and 0.5 microgram/kg, respectively. For confirmation of CAP residues, the relative ion abundance (m/z 466 and 468) was calculated. Further confidence was obtained by comparison of accurate monoisotopic masses from a spectrum library.

Anti-Bacterial Agents↗