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Biomedical subjects

M S Liu

Publications and source records attributed to M S Liu.

At least 91 records · Page 5Linked to original sources
PubMed1986

Analysis of six distinct integrated hepatitis B virus sequences cloned from the cellular DNA of a human hepatocellular carcinoma.

Six distinct hepatitis B virus (HBV) integrations and the flanking cellular sequences were cloned from a hepatoma DNA preparation. None of the cloned fragments retains the entire HBV sequences but the surface antigen (HBsAg) gene and the HBV enhancer are retained in three of the six clones. The other three clones carry only short and possibly highly rearranged HBV genomic sequences and seem to contain some GC-rich clusters. Members of the repetitive Alu family are also found in the vicinity of five of the six integration regions which may have contributed to genome instability. In these six clones, the preferred integration sites are shown to lie within the single-strand region of the HBV genome. None of the clones carries in the flanking cellular sequences any of the 17 oncogenes tested, although the possibility still exists that an oncogene may be found on the side of the genome which has not been cloned. This work thus paves the way for detailed sequence analysis of virus-host junctions, for transfection studies of the HBV integration events, and for a search of genes in the flanking cellular sequences which may have been activated by the retained HBV enhancer using the clones described.

Base Sequence↗
PubMed1986

Mechanisms of endotoxin-induced impairment in Na+-Ca2+ exchange in canine myocardium.

Effects of endotoxin administration on the Na+-Ca2+ exchange in canine cardiac sarcolemma were characterized. In addition, roles of phospholipase A2 and phosphorylation on the endotoxin-induced impairment in Na+-Ca2+ exchange were investigated. The results show that intravesicular sodium (Nai+)-dependent 45Ca2+ uptake was decreased by 39-66% (P less than 0.05) and extravesicular sodium (Nao+)-induced 45Ca2+ efflux was decreased by 36-52% (P less than 0.05) at 2 h following endotoxin administration. Ca2+o-induced 45Ca2+ efflux in the absence of Ko+ was not affected, but Ca2+o-induced 45Ca2+ efflux in the presence of Ko+ was significantly reduced by endotoxin administration. The stoichiometry of Na+-Ca2+ exchange was altered from 3 Na+ for 1 Ca2+ for the control to 2 Na+ for 1 Ca2+ for the endotoxin-treated dogs. The ATP-dependent 22Na+ uptake and Na+-Ca2+ exchange in inside-out vesicles remained unchanged after endotoxin injection. Digestion of control heart sarcolemmal vesicles with exogenous phospholipase A2 (0.02-0.06 unit/500 micrograms protein) inhibited Na+-Ca2+ exchange activity measured as Nai+-dependent 45Ca2+ uptake, and the inhibition was concentration dependent. Lysophosphatidylcholine addition to the control cardiac sarcolemma had no effect on Na+-Ca2+ exchange. The inhibition of Na+-Ca2+ exchange caused by phospholipase A2 digestion in the control heart sarcolemma was completely reversible by the addition of phosphatidylcholine (0.1 mM). The inhibition of Na+-Ca2+ exchange caused by the in vivo administration of endotoxin was completely reversible by the addition of phosphatidylcholine (0.1-0.15 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1986

Myocardial sodium pump activity in endotoxin shock.

The effect of endotoxin administration on the integrity of sodium pump was studied in canine heart myocardium. Sodium pump activity was determined based on the 86Rb+ uptake by ventricular muscle strips. The results show that 4 hr following endotoxin administration the ouabain-sensitive 86Rb+ uptake was inhibited by 44-70%, and the inhibition was noncompetitive with 86Rb+ ions and was independent of Na+ concentrations. The sensitivity of sodium pump toward verapamil inhibition was unaffected by endotoxin administration, suggesting that the endotoxin-induced decrease in sodium pump activity is not mediated through alteration in either calcium or slow sodium channel. The sensitivity of 86Rb+ uptake to ouabain inhibition was decreased approximately sixfold in endotoxin-injected dogs. These data suggest that sodium pump is greatly impaired in dog hearts 4 hr after endotoxin administration. The impairment in sodium pump might have physiological significance in the development of myocardial dysfunction during endotoxic shock.

Animals↗
PubMed1985

Glycolytic and tricarboxylic acid cycle intermediates in dog livers during endotoxic shock.

The effects of endotoxin administration on glycolytic and tricarboxylic acid cycle intermediates in dog livers were studied. Changes in metabolite concentrations were expressed graphically as percentages of controls using "crossover" plots in order to identify transitory rate-controlling steps. The results show that endotoxin administration increased glycolytic flux through pyruvate kinase, inhibited gluconeogenic flux through phosphoenolpyruvate carboxykinase, decreased glycogen storage, shifted cytosolic and mitochondrial redox state from a relatively oxidized to a more reduced state, decreased the extra- and intramitochondrial malate-aspartate and glutamate-alpha-ketoglutarate shuttle activities, depleted ATP, ADP, and NADP concentrations, and decreased energy charge. Based on these data, it is concluded that pyruvate kinase plays the major role in the control of glycolysis, while phosphoenolpyruvate carboxykinase is the major controlling step for the regulation of gluconeogenesis in dog livers during endotoxic shock. In addition, the major factor in the regulation of metabolic pathways that produce and utilize high-energy phosphates in the livers was impaired in endotoxic shock.

Adenine Nucleotides↗
PubMed1985

Photoradiation therapy of cutaneous angiosarcomas in mice.

Cutaneous angiosarcoma is a relatively rare but devastating malignant vascular tumor. It has a high incidence of recurrence following conventional therapeutic modalities applied either singly or in combination. The increased vascularity of cutaneous angiosarcomas, facilitating selective uptake and retention of a photosensitizing agent, such as hematoporphyrin derivative (HPD), suggests that these tumors would respond well to photoradiation therapy. To study the feasibility of this treatment modality, transplantable hemangiosarcomas were implanted in B6C3F1 female mice. Within 2.5 to 3.5 hours after intraperitoneal administration of HPD, fluorescence was recorded in the tumor as compared with surrounding normal skin. When these photosensitized tumors were exposed to 70 J/cm2 of laser energy from an argon-pumped dye laser at 630 nm, the tumors showed marked necrosis within 24 hours. In another series, the tumors were initially photosensitized with HPD for 3 hours and then treated with laser energy ranging from 0 to 96 J/cm2. A dual labeling procedure demonstrated a dose-related decrease in DNA synthesis rate in tumors that were exposed to 0 to 30 J/cm2 at 24 hours after treatment. Furthermore, tumor tissue exposed to laser energy in excess of 30 J/cm2 showed no significant cellular DNA synthesis. These data, supported by histologic evidence of tissue destruction, suggest that photoradiation therapy has a great potential as a therapeutic modality for cutaneous angiosarcomas.

Animals↗
PubMed1984

Kinetic studies of the Na+-K+-ATPase enzyme system in brain and heart of aging rats.

Kinetic analyses of the Na+-K+-adenosine triphosphatase (ATPase) system were performed in brain and heart preparations from young mature (4 mo old) and healthy aged (25 mo old) rats. The K+-activated p-nitrophenylphosphatase (K+-pNPPase) method was used to assess activity of the enzyme system. Ouabain inhibition of K+-pNPPase activity was also examined. A significant age-related decrease in maximal velocity (Vmax) was found in cardiac K+-pNPPase activity, but no changes were seen in the K+ concentration for half-maximal velocity (K0.5). No age differences in Vmax or K0.5 were seen for brain. No differences in ouabain inhibition were found in either brain or heart. In a second experiment, the major component of the age-related decline in cardiac K+-pNPPase activity was found to occur between 5 and 14 mo of age, a period during which plasma thyroxine had previously been found to decline in the same animals. Since peripheral Na+-K+-ATPase activity is partly thyroid hormone dependent, the age-dependent decrease in cardiac enzyme activity appears to be secondary to neuroendocrine changes.

4-Nitrophenylphosphatase↗
PubMed1984

Separation of isoenzymes of glucose-6-phosphate dehydrogenase from human erythrocytes by two-dimensional gel electrophoresis.

Isoelectric focusing performed in 6.0% polyacrylamide gel in the presence of 1.0 M urea separates well the various molecular forms of glucose-6-phosphate dehydrogenase from human erythrocytes. At least seven sharp bands appear in the gel pattern, which vary both in isoelectric points and in the relative intensity. Their isoelectric points are at pH 6.88 for band 1, pH 6.79 for band 2, pH 6.64 for band 3, pH 6.50 for band 4, pH 6.39 for band 5, pH 6.19 for band 6, and pH 6.10 for band 7. A second-dimensional disc electrophoresis performed in a polyacrylamide gel slab resolves each band into two components, a slow and a fast component defined according to their mobilities in the disc gel. The slow component constitutes the major portion of each band. All the seven slow components appear to be dimer having a molecular weight between 98,000-94,000. They belong to "change isomers" having identical molecular size but containing different net changes. The molecular weight of the fast components is between 66,800-50,600. These fast components might be monomer or the digested products of slow components.

Blood Protein Electrophoresis↗
PubMed1983

Change in membrane lipid fluidity induced by phospholipase A activation: a mechanism of endotoxic shock.

The effects of endotoxin administration on the fluidity of dog liver plasma membranes and their relationship with changes in phospholipase A2 activity were studied. Endotoxin administration decreased the fluidity of liver plasma membranes and this decrease was reversible by phosphatidylcholine. The endotoxin-induced decrease in membrane fluidity could be mimicked by digesting control liver membranes with exogenous phospholipase A2. Endotoxin administration also increased the endogenous phospholipase A2 activity. Endotoxin in vitro had no phospholipase A2-like activity but it activated the hydrolytic activity of exogenous phospholipase A2. Based on these data, it is concluded that endotoxin administration decreased the fluidity of canine liver plasma membranes by acting through activation of phospholipase A2. The decrease in membrane lipid fluidity induced by endotoxin administration may play a significant role in the development of the pathophysiology of endotoxic shock at the cellular level.

Animals↗
PubMed1983

Mechanism of endotoxin-induced reduction in the number of beta-adrenergic receptors in dog livers: role of phospholipase A.

The role of phospholipase A on the endotoxin-induced reduction in the number of beta-adrenergic receptors in dog liver plasma membranes was investigated. The results show that digestion of control liver plasma membranes with exogenous phospholipase A2 (0.2 unit/200 micrograms protein) decreased the specific binding of (-)-[3H]dihydroalprenolol by 37.3% (P less than 0.01) and reduced the number of receptor sites by 31.7% (P less than 0.05). These decreases in the specific binding and the number of beta-adrenergic receptors were completely reversible by the addition of phosphatidylcholine (0.2 mM). Endotoxin administration (2 hr postendotoxin) decreased the specific binding by 36% (P less than 0.05) and reduced the number of beta-adrenergic receptors by 33% (P less than 0.05), and these decreases were completely reversible by the addition of 0.2 mM phosphatidylcholine. Digestion of control liver membranes with exogenous phospholipase A2 decreased phosphatidylcholine and phosphatidylethanolamine levels by 50.6 and 51.2%, respectively, but increased lysophosphatidylcholine and lysophosphatidylethanolamine levels by 12- and 8.4-fold, respectively. Endotoxin administration decreased phosphatidylcholine and phosphatidylethanolamine contents by 21.4 and 23.8%, respectively, but increased lysophosphatidylcholine and lysophosphatidylethanolamine contents by 2.1- and 1.4-fold, respectively. In addition, endotoxin administration increased endogenous phospholipase A activity by 73.5%. Based on these results, it is suggested that the decreases in the specific binding and the number of beta-adrenergic receptors in dog livers during endotoxic shock are a result of phospholipase A activation.

Animals↗
PubMed1983

Changes in alpha-adrenergic receptors in dog livers during endotoxic shock.

The effects of endotoxin administration on alpha-adrenergic receptors in dog liver plasma membranes were studied using [3H]dihydroergocryptine as a radioactive ligand. The Scatchard analysis revealed a two-component binding characteristic both in control and endotoxin-injected dogs. The Kd (dissociation constant) of the high-affinity component was increased by 32.5% (0.4 +/- 0.04 nM for control vs 0.53 +/- 0.06 nM for endotoxic; P less than 0.05) with no significant change in the Kd for the low-affinity component (3.0 +/- 0.44 nM for control vs 3.4 +/- 0.44 nM for endotoxic) 2 hr following endotoxin administration. The maximum binding capacity of the high-affinity component was decreased by 38.1% (460 +/- 19.3 and 285 +/- 14.8 fmole/mg protein for control and endotoxic, respectively; P less than 0.01) and that of the low-affinity component was decreased by 34.2% (1050 +/- 66.4 and 690 +/- 44.6 fmole/mg protein for control and endotoxic, respectively; P less than 0.05) 2 hr after endotoxin injection. The competitive inhibition studies show that the apparent Kd values for (-)-epinephrine, (-)-norepinephrine, and prazosin were increased 15, 13, and 25 times, respectively, with no significant change in the apparent Kd values for yohimbine or phentolamine 2 hr postendotoxin. These data demonstrate that the binding affinity of the high-affinity component and the number of alpha-adrenergic receptor binding sites were decreased in endotoxic shock. A modification of the alpha-adrenergic receptors in dog livers induced by endotoxin administration may play an important role in the development of hepatic glucose dyshomeostasis during shock.

Animals↗
PubMed1983

Changes in beta-adrenergic receptors in dog livers during endotoxic shock.

The effects of endotoxin administration on beta-adrenergic receptors in dog liver plasma membranes were studied using [3H]dihydroalprenolol as a radioactive ligand. The Scatchard analysis revealed a one-component binding characteristic both in control and endotoxin-injected dogs. The Kd (dissociation constant) value was increased by 60% (4.2 +/- 0.5 nM for control vs. 6.7 +/- 0.5 nM for endotoxic; P less than 0.01) and the Bmax (maximum binding capacity) was decreased by 38% (600 +/- 60 and 370 +/- 70 fmol/mg protein for control and endotoxic, respectively; P less than 0.01) 2 h following endotoxin administration. The competitive inhibition studies show that the apparent Kd values for (-)-isoproterenol, (-)-epinephrine, and (-)-norepinephrine were increased by 14, 51, and 5 times, respectively, 2 h postendotoxin. In addition, endotoxin in vitro had a dose-dependent inhibitory effect on the specific binding of [3H]dihydroalprenolol, and it also reduced the number of beta-receptors. These data demonstrate that endotoxin, both in vivo and in vitro, decreased the binding affinity and the number of beta-adrenergic receptors in dog liver plasma membranes. A modification of the beta-adrenergic receptors in dog livers induced by endotoxin administration may play an important role in the development of hepatic glucose dyshomeostasis during shock.

Animals↗
PubMed1983

Decrease in adenylate cyclase activity in dog livers during endotoxic shock.

The effects of endotoxin administration on adenylate cyclase in dog liver plasma membranes were studied. The basal, fluoride-, guanine nucleotide-, isoproterenol-, and glucagon-stimulated adenylate cyclase activities were decreased by 61, 62, 69, 83, and 63%, respectively, 2 h after in vivo administration of endotoxin. Endotoxin (100 micrograms/ml) in vitro decreased the guanine nucleotide-, isoproterenol-, and glucagon-stimulated adenylate cyclase activities by 24, 25, and 21%, respectively. These data demonstrate that endotoxin administered in vivo or in vitro had an inhibitory effect on the adenylate cyclase enzyme system in dog liver plasma membranes. Because of the involvement of the adenylate cyclase-adenosine 3',5'-cyclic monophosphate (cAMP) system in the regulation of hepatic carbohydrate metabolism, the finding that endotoxin administration decreased adenylate cyclase activity in the liver should contribute to the understanding of the pathophysiology of altered hepatic glucose homeostasis during shock.

Adenylyl Cyclases↗
PubMed1982

Changes in phase transition temperature of phospholipids induced by endotoxin.

The effects of endotoxin (lipopolysaccharide from Salmonella minnesota Re 595) on the phase transition temperature (Tm) of various phospholipids were studied. Endotoxin had no effect on the Tm and the width of the phase transition of dipalmitoyl-sn-3-phosphatidylcholine. Endotoxin at 100 micrograms/ml increased the Tm of dipalmitoyl-sn-3-phosphatidylethanolamine by 1.1 degrees C (P less than 0.01) and narrowed the range of transition from 4.5 to 2.6 degrees C; the endotoxin-induced changes in the Tm and the transition range were abolished by the presence of 0.25 mM CaCl2. Endotoxin increased the Tm of dipalmitoyl-sn-3-phosphatidic acid by 1.1 (P less than 0.01), 1.2 (P less than 0.01), and 3.1 (P less than 0.01) degrees C at 25, 50 and 100 micrograms/ml, respectively. Furthermore, the width of phase transition of phosphatidic acid was narrowed from 6.5 to 4.0 degrees C by endotoxin at 100 micrograms/ml. The endotoxin-induced changes in the Tm and the transition range of phosphatidic acid were not affected by the presence of EDTA (1 mM) or CaCl2 (0.05-0.1 mM). These results suggest that endotoxin decreases the fluidity of negatively charged phospholipids such as phosphatidic acid and phosphatidylethanolamine. A change in the physical properties of membrane lipid bilayers induced by endotoxin may have an adverse effect on the function of biological membranes.

Endotoxins↗
PubMed1982

Increased incorporation of 14C-palmitate into tissue lipids by isolated heart myocytes in endotoxic shock.

The incorporation of 14C-palmitate into various classes of tissue lipids by isolated adult dog heart myocytes was studied in an attempt to understand the pathophysiology of myocardial dysfunction during endotoxic shock. The results showed that the incorporation of 14C-palmitate into phospholipids was increased by 85.3% and 108.8% at 0.5 hours and two hours, respectively, following endotoxin (0.5 mg Escherichia coli lipopolysaccharide B per kg body weight) administration. Incorporation of radioactive palmitate into triglycerides was increased by 50.9% and 107.2% at 0.5 and two hours, respectively, postendotoxin. Incorporation of 14C-palmitate into diglycerides was stimulated by 51.9% and 64.5% at 0.5 and two hours, respectively, after endotoxin injection. The incorporation of 14C-palmitate into tissue-free fatty acids and unaltered at 0.5 hours but it was increased by 211.7% at two hours postendotoxin. These data demonstrated that myocardial membrane lipid profile was greatly altered by increased incorporation of 14C-palmitate into phospholipids and neutral lipids after endotoxin administration. An alteration in myocardial lipid profile, as reported in this study, may contribute to the development of myocardial dysfunction during shock.

Acyl Coenzyme A↗