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Biomedical subjects

M L Murphy

Publications and source records attributed to M L Murphy.

207 records · Page 12Linked to original sources
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Alteration in calcium metabolism in mitochondria isolated from ischemic and reperfused myocardium.

This study determines the effect of ischemia and reperfusion on energy-linked Ca2+ uptake by myocardial mitochondria. The left anterior descending coronary artery was occluded in 14 mature pigs for 2 hr. In seven animals the ligature was released and the ischemic zone reperfused for 2 additional hours. After sacrifice, mitochondrial function was measured in normal and reperfused or ischemic areas of the left ventricle, using a polarographic method. Mitochondria were prepared without EDTA by standard procedures and Ca2+ uptake measured by 45Ca2+ isotope tracer. Uptake of Ca2+ by mitochondria derived from ischemic myocardium is markedly impaired with or without phosphate. Reperfusion may accentuate this impairment. The presence of exogenous Ca2+ inhibits the ability of ischemic or reperfused mitochondria to phosphorylate ADP.

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Use of polyethylene glycol and fluorocarbon for the purification of avian encephalomyelitis virus.

A simple method is described for isolating avian encephalomyelitis virus (AEV) from a bulk amount of proteins and lipids in a homogenate of infected whole chicken embryos. More than 90% of the virus in the homogenate was precipitated by 4% polyethylene glycol (PEG), and the precipitate was free of approximately 90% of the total nonviral protein. When the homogenate was extracted with fluorocarbon, the aqueous fraction retained the full virus infectivity and about 70% of the protein but was free from most lipid materials. A two-step procedure (precipitation of the homogenate by 4% PEG, followed by extraction of the precipitate by fluorocarbon) gave a 50-fold purification of AEV over the original homogenate. The procedure is simple, rapid, and effective in removing nonviral proteins and lipids from host tissues. It is useful as an initial treatment of embryonic materials for the purification of AEV.

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Purification of avian encephalomyelitis virus by ultracentrifugation in a nonlinear cesium chloride gradient.

A rapid and convenient method is described for purifying avian encephalomyelitis virus. Infected embryo homogenate was treated with polyethylene glycol followed by extraction with fluorocarbon. Extracted sample was pelleted at 73,400 x g, resuspended, and subjected to isodensity centrifugation in preformed nonlinear gradient. A distinctive virus band was observed after centrifugation for 120 min at 192,000 x g. The fraction containing the virus band demonstrated the major portion of infectivity and the presence of the virus particles by electron microscopy. The method was reproducible within a limited number of trials.

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Alterations of membrane potential and Ca2+ flux of sarcoplasmic reticulum vesicles in ischemic myocardium.

The sequence of contraction-relaxation for myocardial cells is believed to be linked to Ca2+ flux across the sarcoplasmic reticulum. Alterations of sarcoplasmic reticulum function during ischemia may result in depressing the myocardial contraction-relaxation sequence. This study examines the relationship between the membrane potential and Ca2+ flux across sarcoplasmic reticulum vesicles isolated from non-ischemic and ischemic myocardium. Ischemic myocardium was produced by ligating the coronary artery of swine hearts for 15 and 30 minutes. Membrane potential was determined by use of the fluorescence-sensitive dye, 3,3'-diethylthiadicarbocyanine, and Ca2+ uptake was studied spectrophotometrically with the use of murexide. Results are as follows: (1) membrane potential and Ca2+ uptake by sarcoplasmic reticulum from ischemic myocardium progressively decreased with the length of ischemia; and (2) preincubation of sarcoplasmic reticulum from non-ischemic myocardium with deoxycholate (0.01 approximately 0.09 percent) resulted in progressively decreasing membrane potential and Ca2+ uptake. Apparently a correlation exists between membrane potential and the rate of Ca2+ uptake. These results suggest that membrane characteristics of sarcoplasmic reticulum are altered within as early as 15 minutes of the onset of ischemia. Alteration of membrane permeability in sarcoplasmic reticulum from ischemic myocardium may be responsible for the observed decrease in membrane potential and Ca2+ uptake.

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PubMedDate not supplied

Glucocorticoid effects on the embryonic chick heart. II. Alteration of oxidative metabolism.

The injection of cortisol phosphate (0.5 mg per egg) onto the chorioallantoic membrane of embryonic chicks at 12 days incubation depresses the rate of oxygen consumption in heart mitochondria isolated from the chicks 24 or 48 hours after the injection as compared to a saline injected control. The oxygen consumption is depressed using either reduced nicotinamide-adenine dinucleotide (NADH)-linked or flavin adenine dinucleotide (FADH)-linked substrates. The progressive inhibition of oxidation and adenosine triphosphate (ATP) production rate is related to the time after cortisol is injected. The treated mitochondria appear to function differently when NADH-linked and FADH-linked respiratory substrates are compared. Using NADH-linked substrates (site 1), adenosine diphosphate (ADP) was phosphorylated by mitochondria, even though the rate of phosphorylation was decreased; however, when FADH-linked substrates were used, incomplete phosphorylation was observed. The rate and the extent of calcium accumulation by embryonic chick heart mitochondria were also depressed by cortisol. These data suggest a defect in phosphorylation at site 2 following cortisol treatment but not at the site 1 linked energy transducing step. Whether these impairments of mitochondrial function result from catabolic turnover of the mitochondrial membrane components, excessive calcium accumulation by the mitochondria, or from the digestion of mitochondrial constituents, has not been delineated.

Adenosine Diphosphate↗