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G Letko

Publications and source records attributed to G Letko.

At least 55 records · Page 3Linked to original sources
PubMed1985

[Isolated exocrine pancreas cells--a model for the study of the pathogenesis of experimental acute pancreatitis].

For elucidation of the very initial phases of pathogenesis of acute pancreatitis an evaluation of the cellular metabolism may be an important question. Therefore we isolated acinar cells from guinea pig and studied them at morphological and biochemical levels. Generally, the cells maintained their typical arrangement of the enzyme granules in the apical region during isolation procedure. The measurement of the parameters of cellular energy metabolism was regarded as essential for determination of functional intactness of the pancreocytes. To this end oxygraphic and fluorescence microscopic methods were applied. The results show that the hydrogen supply of isolated acinar cells can be remarkably improved by addition of glucose or 80 mM succinate which was sensitively recorded by fluorescence microscopic measurement of rhodamine accumulation. The difference between maximal fluorescence and minimal one at excess dinitrophenol can be used as measure for evaluation of the energy state of isolated pancreatic acinar cells.

Acute Disease↗
PubMed1985

A hierarchic approach for experimental investigations into the pathogenesis of acute pancreatitis.

The complexity of pathogenesis and clinical observations of acute pancreatitis demands a simultaneous experimental investigation at various structural and functional levels. The induction of acute pancreatitis by transformation of a pancreatic edema after short-term pancreatic ischemia was used for studies on the contribution of an alteration of energy metabolism to pathogenesis. The experiments demonstrate that in 70 percent of the rats the pancreatic edema was transformed into acute pancreatitis by 20 min ischemia. This was checked by morphological and enzymic means. For studying the influence of short-term ischemia in the cellular metabolism of acinar cells, pancreatic exocrine cells have been isolated from normal pancreas or that altered by ischemia. These cells were morphologically characterized and their capacity of energy metabolism was quantified.

Acute Disease↗
PubMed1984

Citrulline synthesis--a tool for investigation of the mitochondrial energy metabolism.

The conditions under which citrulline synthesis can be used to stimulate mitochondrial energy metabolism were investigated in isolated rat liver mitochondria. At 25 degrees C, with glutamate as substrate, a lag phase of citrulline formation was observed, which was neither detectable in the presence of succinate nor at 38 degrees C with both substrates. After a high-protein diet, a stationary synthesis was seen from the beginning of incubation for both substrates at either temperature. The high-protein diet was applied to reach maximal citrulline synthesis. Citrulline production was found to be enhanced twice to three times as early as after one to two days. Citrulline formation and associated oxygen uptake vs. temperature were checked in the range from 10 degrees C to 42 degrees C. A linear relationship was noted between temperature and reaction rates in the Arrhenius plot, and the share of citrulline synthesis in the total energy transformation increased with rising temperature. Citrulline synthesis was adopted in experiments to determine the equilibrium state of the adenine nucleotide translocator at 38 degrees C. Just as at 25 degrees C, the translocator operated under disequilibrium conditions at body temperature, too, and the loss of free energy was--3.2 kJ X mol-1.

Animals↗
PubMed1984

[Isolated acinus cells in the significance of ischemia in the pathogenesis of acute pancreatitis].

Additionally to the pancreatic edema short-time ischemia represents an essential factor in formation of an experimentally induced acute pancreatitis. The consequences of such an ischemia at the guinea pig pancreas on the cellular energy metabolism were investigated in isolated exocrine cells. It was shown that intact acinus cells can be isolated as well as from normally perfused and ischemic pretreated pancreata. The energy metabolism was characterized by the difference between resting and maximum respiration after stepwise uncoupling. This parameter represents a dynamic measure and allows an estimate of the load capacity of the cellular energy metabolism. Exocrine cells isolated after ischemia (20 minutes), had a smaller load capacity than cells from normally perfused pancreata. This indicates an alteration of energy supply after ischemia. The consequences of this reduced supply on energy dependent repairing and protective mechanisms are discussed in terms of the pathogenesis of acute pancreatitis.

Acute Disease↗
PubMed1983

Control of mitochondrial respiration.

The control theory of Kacser and Burns [in: Rate Control of Biological Processes (Davies, D.D. ed) pp. 65-104, Cambridge University Press, London, 1973] and Heinrich and Rapoport [Eur. J. Biochem. (1974) 42, 97-105] has been used to quantify the amount of control exerted by different steps on mitochondrial oxidative phosphorylation in rat-liver mitochondria. Inhibitors were used to manipulate the amount of active enzyme. The control strength of the adenine nucleotide translocator was measured by carrying out titrations with carboxyatractyloside. In state 4, the control strength of the translocator was found to be zero. As the rate of respiration was increased by adding hexokinase, the control strength of the translocator increased to a maximum value of approximately 30% at approximately 80% of state 3 respiration. In state 3, control of respiration is distributed between a number of steps, including the adenine nucleotide translocator, the dicarboxylate carrier and cytochrome c oxidase. The measured values for the distribution of control agree very well with those calculated with the aid of a model for mitochondrial oxidative phosphorylation developed by Bohnensack et al. [Biochim. Biophys. Acta (1982) 680, 271-280].

Adenosine Diphosphate↗
PubMed1983

Influence of precursors of biosyntheses on the energy metabolism of the liver cell.

The influence of variable energy demand on both the total ATP/ADP ratio and the rate of respiration was investigated in isolated hepatocytes. For hepatocytes respiring at the same rate, different ATP/ADP ratios were observed when the energy drain was caused either by ureogenesis and gluconeogenesis or by partial uncoupling. These differences were provoked by an additional effect of the precursors of syntheses studied, i.e. lactate or ornithine, on the hydrogen supply of the respiratory chain, as was reflected in terms of the reduction degree of cytochrome c in isolated mitochondria. For a fixed hydrogen supply there exists a defined characteristic ATP/ADP ratio versus rate of respiration. It is concluded that the respiratory rate, the mitochondrial redox state and the phosphorylation potential (transmitted into the extramitochondrial one by the adenine nucleotide translocator) represent a system of three interdependent parameters. The presence of metabolic precursors such as ornithine and lactate enhances the load of the cellular energy metabolism as well as the energy supply of the cell, the latter through improvement of substrate utilization. The ambivalent character of the precursors makes possible a kind of forward optimization of the hepatic energy metabolism which allows the cell to perform syntheses at a relatively high ATP/ADP ratio and, unless syntheses take place, to save energy by avoiding higher ATP/ADP ratios.

Adenosine Diphosphate↗
PubMed1982

Rate-controlling steps of oxidative phosphorylation in rat liver mitochondria. A synoptic approach of model and experiment.

The contribution of different steps to the control of oxidative phosphorylation in isolated rat liver mitochondria was investigated by a combination of experiments and computer simulations. The parameters of the mathematical model of phosphorylating mitochondria were derived from experimental data. The model correctly described the competition between ATP utilization inside and outside mitochondria for the ATP generated in mitochondria. On the basis of the good agreement between experiments and simulations, the contribution of different steps to the control of respiration was estimated by computing their control strengths, i.e., the influence of their activities on the rate of respiration. The rate-controlling influences vary depending on the load of oxidative phosphorylation. The predominant steps are: in the fully active state (State 3)--the hydrogen supply to the respiratory chain; in the resting state (State 4)--the proton leak of the mitochondrial inner membrane; in states of non-maximum ATP export--the adenine nucleotide translocator. Titrations of respiration with phenylsuccinate, antimycin, oligomycin and carboxyatractyloside completely support these conclusions.

Adenosine Diphosphate↗
PubMed1982

[An objective rapid testing method for viability of corneal endothelium after conservations (author's transl)].

An objective procedure for assessing damage to corneal endothelium is described; it is based on photometrical determination of the dye toluidine blue absorbed by damaged cells. This inexpensive quick test is suitable both for preoperative assessment of grafts and for checking procedures for cornea conversation. The use of the peripheral region of the endothelium enables the remaining central trephined portion in transplantations. When this procedure was used to conserve pig corneae in the moist chamber there was a slight increase in damage by the ninth day. By the 17th day all the endothelial cells were damaged.

Animals↗
PubMed1982

Interrelationship between oxidative energy transformation and energy consumption at mitochondrial and cellular levels.

The adaptation of oxidative energy transformation in mitochondria to the energy demand of cellular metabolism was investigated in experiments with isolated mitochondria and liver cells and by computer simulation in terms of a mathematical model. Separate draining of different energy pools allowed the determination of the relation between these pools and the elucidation of the importance of the connecting enzyme reactions to the regulation of the whole process. The following conclusions can be drawn from the results: 1. The intramitochondrial adenine nucleotide pool exhibits a homogeneous behaviour, and its changes are the signal for ATP synthesis. 2. The proton-motive force which is in near-equilibrium with the intramitochondrial phosphorylation potential is the immediate signal for the respiratory chain. 3. The intramitochondrial phosphorylation potential is transformed into the external one by a flux-dependent non-equilibrium reaction of the translocator. 4. The rate of respiration-linked ATP formation is regulated by more than one reaction step with varying control strength. 5. In both isolated mitochondria and hepatocytes an activation of respiration is provoked by a decrease in the mitochondrial energy state caused by cellular energy utilization.

Adenosine Triphosphate↗
PubMed1981

Relationship between the energy cost of ATP transport and ATP synthesis in mitochondria.

Liver mitochondria form rats kept on a high-protein diet exhibit an increased rate of respiration upon addition of ornithine in the presence of HCO2 and NH+4. This is the manifestation of intramitochondrial utilization of ATP for the synthesis of citrulline. State 3 respiration of these mitochondria could be adjusted to the same rate as that produced by ornithine by either using limiting amounts of hexokinase or titration with atractyloside. Under such conditions, in both systems the proton-motive force, the intramitochondrial ATP/ADP ratio and the redox state of the respiratory chain were the same. In contrast to this, the ATP/O ratio (equal to 2 X citrulline/O ratio) in mitochondria synthesizing citrulline was higher than the glucose 6-phosphate/O ratio in the system where ATP was trapped extramitochondrially. The ratio of these two ratios was close to 1.5 with both glutamate and succinate as respiratory substrates. From these results it can be concluded that the translocation of ATP against ADP and phosphate utilizes an amount of the chemiosmotic proton gradient equal to half of that needed for the synthesis of ATP in the inner compartment.

Adenosine Diphosphate↗
PubMed1981

Influence of different energy drains on the interrelationship between the rate of respiration, proton-motive force and adenine nucleotide patterns in isolated mitochondria.

The respiration of rat liver mitochondria was stimulated by three different ways of energy drain: (a) partial uncoupling (equivalent to direct collapse of the proton-motive force), (b) intramitochondrial utilization of ATP for citrulline synthesis, and (c) extramitochondrial utilization of ATP for glucose phosphorylation. At identical rates of respiration, the intramitochondrial ATP : ADP ratios were the same in all three systems. Furthermore, the proton-motive force was the same in partially uncoupled mitochondria and in the presence of hexokinase plus glucose up to a respiration rate amounting to about 60% of that of the fully active state. However, external ATP : ADP ratios were considerably different in various systems at comparable rates of oxygen uptake, being the lowest under conditions when ATP was being utilized externally. On this basis, it is concluded that the respiratory rate is controlled directly by the proton-motive force and the mitochondrial ATP-synthesizing system operates under near-equilibrium conditions with respect to the membrane energy state parameters. However, a disequilibrium exists at the step of the transport of ATP from mitochondria to the external (cytoplasmic) compartment.

Adenosine Diphosphate↗
PubMed1980

Investigation of the dependence of the intramitochondrial [ATP]/[ADP] ratio on the respiration rate.

The relationship between the respiration rate and the intra- and extramitochondrial adenine nucleotides was investigated in isolated rat liver mitochondria. For the determination of adenine nucleotide patterns in both compartments a new procedure was developed, based on the evaluation of these metabolites from incubation of various amounts of mitochondria under identical stationary states of oxidative phosphorylation. These identical states were adjusted by addition of appropriate amounts of hexokinase to a glucose-containing incubation mixture. Adenine nucleotides were measured in aliquots of the total extract of the incubation mixture without any separation. The concentrations of the adenine nucleotides in both compartments were obtained from a plot of the total concentration of these species versus mitochondrial protein. Disturbances of this method by unspecific efflux of adenine nucleotides could be excluded. The results obtained for the total adenine nucleotide content (12 nmol . mg-1 protein) and the intramitochondrial [ATP]/[ADP] ratio (about 4 in the resting state) are in good agreement with data obtained by other methods. Strong evidence is provided for a decrease in the intramitochondrial [ATP]/[ADP] ratio with increasing rate of oxygen consumption. Therefore it is not necessary to assume a microcompartmentation of the intramitochondrial adenine nucleotide pool in respect to the ATPase reaction and the adenine nucleotide translocation.

Adenosine Diphosphate↗