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Biomedical subjects

M Fabian

Publications and source records attributed to M Fabian.

At least 37 records · Page 2Linked to original sources
PubMed1990

Spectral and catalytic properties of cytochrome oxidase in organic solvents.

Isolated bovine heart cytochrome oxidase has been extracted into n-hexane, probably in reverse micelles, by the use of asolectin and calcium. The diluted extracts are composed of particles with the hydrodynamic radius of 42 nm. Spectral characteristics of the extracted oxidase are similar to those in aqueous solutions. At the high molar ratio of water to phospholipid (W0 = 8) in an organic solvent both cytochrome a and a3 are reducible and oxygen uptake is observed. However, at low W0 (W0 = 1.8) the rate of cytochrome a reduction is decreased and reduction of cytochrome a3 is inhibited.

Animals↗
PubMed1989

The effect of pH changes on the optical spectrum of oxidised cytochrome oxidase.

The sensitivity to pH changes of oxidised cytochrome oxidase, oxidised oxidase-cyanide and oxidase-azide complexes was investigated by optical difference spectroscopy in the pH region 6.0-8.2. The responses of the optical spectrum of oxidised oxidase and the oxidase-cyanide complex are almost fully developed within some minutes after a pH change of 1-2 units. A blue shift of the spectrum of oxidised oxidase and the oxidase-cyanide complex is observed with decreasing pH, whereas the oxidase-azide complex is almost insensitive to the pH change. From the pH insensitivity of the oxidase-azide complex and the differences in the pH-induced spectral changes of the oxidase-cyanide complex relative to unliganded oxidase, it is concluded that the spectral pH sensitivity in the oxidised enzyme is probably associated with proton binding at or near cytochrome a3 only. Similar absorption changes are observed with the oxidised oxidase on increasing the pH and on the binding of azide to oxidised oxidase at constant pH. It is suggested that azide binding is probably associated with the deprotonation of some ionizable group(s) in the vicinity of the cytochrome a3-CuB site.

Animals↗
PubMed1987

Two-electron reduction is required for rapid internal electron transfer in resting, pulsed and oxygenated cytochrome c oxidase.

The resting as well as the 420 nm and 428 nm forms of cytochrome oxidase have been studied in kinetic experiments with an excess of enzyme over reduced cytochrome c. No difference was found in the behavior of the two activated forms. With all three forms, a fraction of cytochrome a was reoxidized with a rate which was much lower than kcat. This suggests that intramolecular transfer to the dioxygen-reducing site occurs only if both cytochrome a and CuA are reduced. An initial rapid phase in the oxidation of cytochrome a in the pulsed and oxygenated enzymes is related to the presence of a three-electron-reduced dioxygen intermediate. The increased catalytic activity of pulsed and oxygenated oxidase can be explained on the basis of a shift in the redox equilibrium between cytochrome a and CuA.

Animals↗
PubMed1987

Epicardial electrical activation analyzed via frequency-wavenumber spectrum estimation for the characterization of arrhythmiagenic states.

The application of a new signal processing methodology to the analysis of epicardial array ECG signals is presented as an alternative to isopotential or isochrones mapping by the use of a zero-delay wavenumber spectrum (ZDWS) estimation technique. The methodology "explains" the array data as the sum of modulated wideband (non-sinusoidal) propagating waves projected onto the array plane and provides an accurate estimate of their number and bearing. The slowness distribution of each of the waves is then obtained by estimating their temporal spectrum. In this experimental study the effects of localized noninfarcting reversible low flow ischemia, digoxin toxicity and verapamil reversal of digoxin toxicity are quantified via the ZDWS methodology and are compared with the information that can be extracted from isopotential mapping. It is demonstrated that the ZDWS methodology permits the epicardial electric activation to be decomposed into a number of quantification parameters which possess a hierarchical "tree" structure and therefore provide a means for an objective and robust characterization of the effects of agents which alter myocardial conduction and arrhythmia generation.

Animals↗
PubMed1987

Advanced signal-processing method for the detection, localization, and quantification of acute myocardial ischemia.

In this study of a canine heart model of localized reversible ischemia, a computer-based single-processing method is developed to detect and localize the epicardial projections of ischemic myocardial electrocardiograms (ECGs) during the cardiac activation, rather than the repolarization, phase. This is done by transforming ECG signals from an epicardial sensor array into the multichannel spectral domain and identifying three decision variables: (1) the frequency in hertz of the spectral peak (f0), its frequency band width 50% below the peak value (w0), and the maximum eigenvalue difference of the ECG signal's autocorrelation matrix (e0). With use of the histograms of the f0, w0, and e0 parameters of 3256 ECGs from normal and 957 from ischemic areas of myocardium obtained from 12 dogs, it was possible to predict ischemia in a new test group of nine animals from a Neyman-Pearson (NP) test in which the threshold probabilities of detecting ischemia for each decision variable are compared with those of detecting normality. Quantification of each sensor area by the NP tests revealed that, compared with the control, ECG spectra with decreased F0 and w0 and increased e0 relative to their respective thresholds had increased myocardial lactate (p less than 0.01), decreased adenosine triphosphate (ATP) (p less than 0.05), and reduced creatine phosphate (p less than 0.01). Prediction of f0 (p less than 0.0006) as a continuous variable could be obtained from the regression of the myocardial levels of ATP plus creatine phosphate, which demonstrated that this decision variable appears to directly reflect myocardial energetics. It appears that an advanced signal-processing method for ECG array data can be used to detect, localize, and quantify reversible myocardial ischemia.

Adenosine Triphosphate↗
PubMed1981

[Structural-functional characteristics of photosynthetic reaction centers extracted by treatment with lauryldimethylamine oxide from Rhodopseudomonas sphaeroides (wild type)].

A method for isolation of photoactive reaction centers from Rps. sphaeroides (wild type) chromatophores, using lauryldimethylamine oxide (LDAO) as detergent, is described. The preparation obtained is free of a light-harvesting pigment-protein complex and cytochromes. A high degree of purity can be demonstrated from the adsorption indexes of the preparation equal to A280 : A800 = 1.2--1.3; A760 : A800 : A870 = 1 : 2 : 0.9. Data from polyacrylamide gel electrophoresis suggest that the integral protein component of the preparation is made up of three polypeptides with molecular weights of 30 000, 24 000 and 20 000. Under continuous illumination the preparation exhibits an effective electron transfer from the bacteriochlorophyll dimer (BChl)2 to a system of quinone acceptors (X1, X2). The ambient potential Em of (BChl)2 half-recovery was estimated as + 475 mV and pH 7.2. The rate constant for direct electron transfer from X1- to X2 is about 0.5 . 10(3) s-1 at 300 degrees K (0.01 M phosphate buffer; 0.05% LDAO, pH 7.2). The activity of this transfer is exponentially reduced with a decrease in temperature within the range of 300 to 230 degrees K, with an activation energy, Ea, of approximately equal to 8 kcal. The recombination rate constant of light-induced ion-radicals, (BChl)2+ and X1-, was found to be 5 . 10(-2) s-1 at 180 degrees K. The preparations thus obtained can be used for studying mechanisms of primary events in photosynthesis and electron-exchange conformations in the reaction center.

Bacterial Proteins↗
PubMed1979

Thermal quantification of region myocardial perfusion and heat generation.

A technique for experimental determination of regional myocardial blood flow and heat generation has been developed, based on a heat-clearance method. This method allows repetitive and frequent measurements of regional blood flow without necessity for biopsy or microspheres. Testing was performed on a pedicle preparation, an intact segment of left ventricular myocardium dependent on a single diagonal coronary artery and situated in situ in the left ventricular free wall. Total blood flow to the pedicle was measured by an electromagnetic flow probe. A specially designed 3-thermistor microprobe was positioned in the pedicle to continuously sense temperature changes in the subepicardium, midmyocardium, and subendocardium. The theory underlying this method is based on a heat balance that includes local myocardial heating, conduction, and convection. Comparison of the predicted time- and position-dependent temperature with that measured experimentally allows extraction of the local myocardial blood flow and heating rates. This method allows resolution of differential flows in subendocardial, midmyocardial, and subepicardial myocardium and provides quantification of dynamic flow changes in each layer in response to various stimuli such as ischemia or pressor agents, without in itself causing damage to the myocardial microvasculature. Our data show total flow, based on summation of thermally calculated regional flows, to have correlation coefficients of 0.88 with both the flowmeter and microsphere results. Resting flow values for Nembutal-anaesthetized, open-chest dogs of 0.66 ml/(g . min) compare favorably with values obtained by microsphere studies. Infusion of norepinephrine increased total flow and all layer flows, but the increase in subendocardial flow with norepinephrine was less than the increase of the other layers, perhaps accounting for the vulnerability of this region during catecholamine stress. Local myocardial heating rates in subepicardial, midendocardial, and subendocardial layers are shown to follow the same dependence on local myocardial blood flow in response to anoxic stress or norepinephrine-induced vasodilation. Specifically, local heating rate increases to a factor of 10 at flow below resting level.

Animals↗
PubMed1969

The clearance and antidiuretic potency of neurohypophysial hormones in man, and their plasma binding and stability.

1. Bio-assay techniques have been used to measure plasma levels of neurohypophysial hormones in man, following either a single injection or a continuous infusion.2. The median half-life of oxytocin after a single injection of 2 u. was 3.2 min (2.0-5.7, 95% confidence limits); this increased significantly (P < 0.01) to 4.8 min (4.4-6.1) when the hormone was infused at a rate of 500 m-u./min. The vasopressins had appreciably longer half-lives. After a single injection of 1 or 1.5 u. 8-lysine vasopressin (LVP), the half-life was 5.7 min (3.6-6.0). Continuous infusions of the hormones at a rate of 120 m-u./min yielded half-lives of 5.5 min (5.0-7.1) for LVP, and 5.6 min (3.9-9.5) for 8-arginine vasopressin (AVP).3. The apparent volumes of distribution of the hormones were all of the order of two thirds the extracellular volume.4. In accordance with its shorter half-life, the clearance of oxytocin was greater than that of the vasopressins (1.5 l./min, compared with 1.0 l./min).5. The antidiuretic potencies of the hormones were studied in over-hydrated subjects, by measuring the rate of urine excretion following an I.V. injection. Duration of antidiuretic action increased in the order: oxytocin, LVP, AVP. A 5:1 mixture of oxytocin and AVP was not as long-lasting as AVP alone. 8.5% (4-22) of an administered dose of AVP was excreted in the urine, and this amount was significantly correlated with urine volume (r = +0.67, P < 0.05).6. Ultrafiltration of human plasma containing exogenous hormones showed that 30% (13-50) of AVP was bound, the degree of binding being independent of concentration over the range used (50-400 mu-u./ml.) In contrast, oxytocin was completely unbound.7. Exogenous oxytocin was more stable than exogenous AVP in human plasma. At 4 degrees C there was no significant loss of oxytocin until 7 days, whereas 20% of AVP was inactivated in 2 days. At 37 degrees C a 20% loss of AVP occurred within 4 hr, and a 50% loss within 24 hr; corresponding times for oxytocin were 24 and 48 hr.

Adult↗