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Biomedical subjects

M Michalik

Publications and source records attributed to M Michalik.

At least 19 recordsLinked to original sources
PubMed1992

Glutamate production in islets of Langerhans: properties of phosphate-activated glutaminase.

Homogenates of rat pancreas, pancreatic islets, and HIT-T15 cells (a clonal line derived from B cells) catalyzed the breakdown of glutamine to glutamate. This activity was markedly stimulated by the addition of orthophosphate and was much greater in homogenates from islets and the B-cell-derived clonal cell line than in those from whole pancreas. Islet glutaminase was half-maximally stimulated with 40 mmol/L phosphate. Kinetic analyses of the rates of glutamine hydrolysis showed that the Vmax for the reaction increased with the increase in phosphate concentration, whereas the Km for glutamine (2.6 +/- 0.2 mmol/L) was unaltered. The pH optimum for enzyme activity was 8.0 to 8.5 at all phosphate concentrations studied. Glutamine breakdown was enhanced by adenosine triphosphate ([ATP] approximately 100% at 10 mmol/L) and citrate (approximately 30% at 10 mmol/L), but it was unaffected by malate, 2-oxoglutarate, lactate, and ammonia. Glutamate significantly inhibited glutamine hydrolysis. Freshly isolated islets had a low content of both glutamate and glutamine. After culturing for 1 hour in an amino acid-containing medium, the concentrations of glutamine and glutamate increased. Subsequent perifusion without amino acids caused a loss of glutamine and a concomitant increase in glutamate level. Perifusion with 1 mmol/L glutamine led to an increase in both internal glutamine and glutamate. The addition to the perifusion medium of either 10 mmol/L glutamine, 10 mmol/L orthophosphate, or both substantially enhanced insulin release evoked by 10 mmol/L leucine.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1992

Differential in vivo and in vitro effect of gentamicin on glutamate synthesis and glutamate deamination in rabbit kidney-cortex tubules and mitochondria.

The effect of gentamicin on both glutamate synthesis and glutamate deamination was studied in kidney-cortex mitochondria and tubules isolated from both control and gentamicin-treated animals. In kidney-cortex mitochondria which were permeabilized in order to make a free access of substrates and antibiotic to the glutamate dehydrogenase, gentamicin appeared to be a very potent inhibitor of glutamate synthesis, resulting in about 60% decrease of the enzyme activity at 5 mM concentration. Other aminoglycoside antibiotics decreased the enzymatic activity, in the following order: gentamicin > neomycin = tobramycin = kanamycin > biodacyna > amikacin > streptomycin. This, in principle, corresponds to their known nephrotoxic potential observed in vivo. The inhibitory action of antibiotics was abolished by neither ADP nor leucine, allosteric activators of glutamate dehydrogenase. Surprisingly, gentamicin did not decrease the rate of ammonia formation from glutamate when added to both renal tubules and mitochondria isolated from control rabbits. This indicates that the antibiotic exerts its inhibitory effect on glutamate dehydrogenase activity in the direction of glutamate synthesis only. In contrast, the rate of both glutamate deamination and glutamate synthesis was about 40% lower in renal tubules and mitochondria isolated from kidney-cortex of animals which were given antibiotics for 10 days. In view of these results it seems that (i) the depression of ammoniagenesis in gentamicin-treated animals may be due to a decrease of glutamate dehydrogenase content and (ii) under conditions in vitro the aminoglycoside inhibits the enzyme activity in the direction of glutamate synthesis while it does not affect the glutamate deamination.

Adenosine Diphosphate↗
PubMed1991

Recovery of impaired gluconeogenesis in kidney-cortex tubules of gentamicin-treated rabbits.

Rabbits were given gentamicin over a period of 10 days. At 1, 3, 5 and 10 days renal proximal tubules were isolated and glucose synthesis from several substrates was measured. A relationship between the inhibition of renal gluconeogenesis, accompanied by a decline of both pyruvate carboxylase and phosphoenopyruvate carboxykinase (PEPCK) activities, and an increased gentamicin level in kidney-cortex was noticed after 5 days of therapy. Both the rates of glucose formation from various substrates as well as pyruvate carboxylase and the cytosolic PEPCK activity recovered fully within 3 weeks after cessation of antibiotic treatment while an increase of activity of the mitochondrial PEPCK occurred during chronic administration of the drug for 10 days. It is concluded, that gentamicin-induced inhibition of gluconeogenesis is one of the events occurring during complex action of this drug on renal cortex.

Animals↗
PubMed1990

Classification of brain tumours by CT-image Walsh spectra.

Besides clinical and anamnestic data, image information from CT-image data in the tumour border was used for classification of brain tumours. If the image regions are properly selected a classification rate of 85% is obtained with a hierarchic classifier, although our study is based on only 139 patients.

Algorithms↗
PubMed1990

[Typical CT findings with the intrathecal infusion test in post-traumatic disorders of cerebrospinal fluid dynamics].

Simultaneous computer tomographic and cerebrospinal fluid dynamics examinations in patients with high-pressure hydrocephalus, normal pressure hydrocephalus and cerebral atrophic processes are presented and discussed. Exclusive CT and MR examinations do not allow a differentiation of patients with normal pressure hydrocephalus and patients with cerebral atrophy. In the simultaneous examinations the morphological substrate during the intrathecal infusion test is represented.

Adult↗
PubMed1989

[Grading of brain tumors using computer-assisted analysis of CT images and anamnestic data].

For the classification of various brain tumours data from 139 patients with histologically proven diagnosis were used. With linear discriminant analysis and hierarchic classification of clinical and anamnestic data and features obtained by Walsh-transformation of image data presently 7 classes of tumours are differentiated with an estimated classification rate of 85% and reclassification rate of 92%.

Brain Neoplasms↗
PubMed1989

[What does the neurologist expect from interventional neuroradiology?].

The methods of interventional radiology require interdisciplinary cooperation. For bioptic methods also a cooperative formulation of the diagnosis is important, while for the occlusion or dilatation of vessels the whole proceeding necessarily is cooperative. The pathophysiologic processes in partial or total ischaemia of the central nervous system can be treated only by a complex periinterventional therapy program carried out by an experienced neurologic intensive care team.

Cerebrovascular Disorders↗
PubMed1989

[Computerized tomography and electroencephalography findings in post-traumatic brain edema].

The reduction in size of the ventricular areas in the computer tomogram as a morphological substrate of a generalised cerebral edema in 43 patients correlated better with the vigilance than with the EEG findings. This fact as well as the representation possibility of additional intracranial haemorrhages favour the computer tomography in the posttraumatic acute phase as compared to the electroencephalography, which should be employed in the subacute phase.

Adolescent↗