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Biomedical subjects

A T Quintanilha

Publications and source records attributed to A T Quintanilha.

16 recordsLinked to original sources
PubMed1991

Hemoglobin polymerization in sickle cells studied by circular polarized light scattering.

We have studied intracellular polymerization of hemoglobin S in suspensions of small populations of sickle cells using circular polarized light scattering. We argue that the preferential scattering of right circular polarized light (as expressed by measurements of the S14 Mueller scattering matrix element) directly reflects the amount of polymer inside cells. This technique has made it possible to investigate the effect of oxygen tension, cell density and osmotic stress on intracellular hemoglobin polymerization. Using S14 to determine hemoglobin polymer, we show that the polymer increases with deoxyhemoglobin concentration, that cells containing higher hemoglobin concentrations show significantly more polymer than cells containing less hemoglobin, and that polymerization occurs in sickle-trait cells in hypertonic solutions as the oxygen tension in the suspension is reduced. We also present kinetic measurements of polymerization, including that induced by osmotic shock. Finally, we demonstrate that the total light scattered (S11 Mueller scattering matrix element) that is routinely measured simultaneously with S14 can be used to estimate the percent of reduced (deoxy) Hb in the sample. These experiments demonstrate the potential of this technique to monitor hemoglobin polymerization simultaneously with oxygen dissociation under a wide variety of physiological conditions.

Erythrocytes↗
PubMed1984

Exercise endurance-training alters vitamin E tissue levels and red-blood-cell hemolysis in rodents.

Muscle tissue levels of d1-alpha-tocopherol (vitamin E) were significantly lower in endurance-trained rats than in sedentary animals, whether the animals were fed on vitamin-E-deficient or control (vitamin-E-sufficient) diets. In vitamin-E-deficient rats, liver tissue levels of vitamin E were significantly lower in those that were endurance-trained than in those that were sedentary; this was not the case in control animals. In addition, for vitamin-E-deficient rats, the onset of red-blood-cell hemolysis in the sedentary animals occurred one week earlier than in the endurance-trained animals. Thus, it appears that training induces a protective effect against hemolysis despite vitamin E deficiency.

Animals↗
PubMed1983

Vitamin E, physical exercise and tissue oxidative damage.

Oxidative damage and the role of antioxidants and prooxidants in aerobic metabolism is of great current interest; it spans areas of research such as carcinogenesis, ageing, toxicology and nutrition. We have used Bantin-Kingman female rats for both in vivo and in vitro studies. In these animals we have altered the levels of all-rac-alpha-tocopherol (vitamin E) by dietary means and have used physical exercise and visible light exposure to alter oxidative stress. Our results show a progressive and specific increase in the susceptibility of many subcellular membranes to oxidative damage with increasing levels of vitamin E deficiency and/or physical stress. In addition, endurance training raised the levels of antioxidative enzymic pathways in both skeletal and cardiac muscle.

Animals↗
PubMed1982

Membrane effects of vitamin E deficiency: bioenergetic and surface charge density studies of skeletal muscle and liver mitochondria.

Vitamin E deficiency in rats increased the sensitivity of liver and muscle mitochondria to damage during incubation at various temperatures, irradiation with visible light, or steady-state respiration with substrates. In all cases, vitamin E-deficient mitochondria exhibited increased lipid peroxidation, reduced transmembrane potential, decreased respiratory coupling, and lower rates of electron transport compared to control mitochondria. Muscle mitochondria always showed greater negative inner membrane surface charge density, and were also more sensitive to damage than were liver mitochondria. Vitamin E-deficient mitochondria also showed slightly more negative inner membrane surface charge density compared to controls. The relationship observed between greater negative surface potential and increased sensitivity to damage provides for a new and sensitive method to probe further the role of surface charge in membrane structure and function. Implications of these new findings for the well-known human muscle myopathies and those experimentally induced by vitamin E deficiency in animals are discussed.

Animals↗
PubMed1980

Surface charge changes in purple membranes and the photoreaction cycle of bacteriorhodopsin.

The surface potential of purple membrane fragments, determined from the distribution of the aqueous free and the membrane-bound positively charged, paramagnetic, amphiphilic probe 4-(dodecyldimethylammonium)-1-oxyl-2,2,6,6-tetramethylpiperidine bromide varied almost 60 mV as a function of ionic strength and 50 mV as a function of pH of the medium. Light-induced changes in surface potential followed the changes observed in the M412 intermediate of the photocycle of bacteriorhodopsin as a function of pH, temperature, and response to antibiotics beauvericin and valinomycin. The number of induced charges per M412 appearing at the surface of purple membranes decreased from about 0.75 to 0.45 as the surface potential became more negative. The stoichiometry would be twice as large if the charge changes were localized exclusively on one side of the purple membrane. Laser flash-induced kinetics of the rise and decay of surface charge changes were slightly slower than the kinetics of the rise and decay of M412 which is associated with the reversible deprotonation of the retinal Schiff base nitrogen in the chromophore. It is suggested that the light-induced charge changes monitor a dissociable amino acid residue which may be a step in the movement of protons across the purple membrane.

Bacteriorhodopsins↗
PubMed1978

Damage to mitochondrial electron transport and energy coupling by visible light.

The effect of treating mitochondria with visible light above 400 nm on electron transport and coupled reactions was examined. The temporal sequence of changes was: stimulation of respiration coupled to ATP synthesis, a decline in ATP synthesis, inactivation of respiration, increased ATPase activity and, later, loss of the membrane potential. Loss of respiration was principally due to inactivation of dehydrogenases. Of the components of dehydrogenase systems, flavins and quinones were most susceptible to illumination, the iron-sulfur centers were remarkably resistant to being damaged. Succinate dehydrogenase was inactivated before choline and NADH dehydrogenase. Redox reactions of cytochromes and cytochrome c oxidase activity were unaffected. Inactivation was O2-dependent and prevented by anaerobiosis or the presence of substrates for the dehydrogenases. Light in the range 400-500 nm was most effective and the presence of free flavins greatly enhanced inactivation of all of the above mitochondrial activities. This suggests that visible light mediates a flavin-photosensitized reaction that initiates damage involving participation of an activated species of oxygen in the damage propagation.

Animals↗
PubMed1977

Surface localization of sites of reduction of nitroxide spin-labeled molecules in mitochondria.

The relative rates of reduction of several spin-labeled molecules that partition differently across the hy-drophobic-interface of inner membranes from rat liver mitochondria were investigated. Spin labels localized either deep in the hydrophobic region or in the aqueous phase are only slowly reduced; however a spin-labeled analogue of the cationic detergent cetyltrimethylammonium bromide that partitions at the interface is rapidly reduced by coupled electron transport. Chemical studies on the reduction and oxidation of the spin label show that loss of signal is due to reduction and not destruction of the label. No evidence was found for flip-flop of the label in submitochondrial preparations. Spin reduction of respiring mitochondria, mitoplasts, or inverted submitochondrial preparations is inhibited by rotenone but is relatively insensitive to antimycin A and KCN. Because the midpoint potentials of the spin labels were found to be similar to that of ubiquinone, it is concluded that reducing equivalents of mitochondrial electron transport from this region of the chain are channeled to either membrane interface.

Aerobiosis↗