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Biomedical subjects

S C Liu

Publications and source records attributed to S C Liu.

At least 163 records · Page 9Linked to original sources
PubMed1978

Public beliefs about causes and prevention of heart attacks.

Interviews with a probability sample of 617 adults in the Chicago area indicated widespread lack of information about major probable causes of heart attacks in persons younger than 60 years: 28% named cigarette smoking, 21% named high blood pressure, and 13% named cholesterol or fat in the diet or blood. Half did not name any of these risk factors, and only 1% named all three. Although three fourths believed that heart attacks are preventable, few named specific behaviors that would effectively reduce risk factors other than smoking. Sustained community-wide educational programs about reducing coronary risk factors are clearly needed and can be effective.

Adult↗
PubMed1978

Isolation and serial cultivation of rabbit skin epithelial cells.

A method to isolate and to serially cultivate rabbit skin epithelial cells from adult trunk skin has been developed. Using a collagen gel as substrate and trypsin and EDTA to dissociate cells, nonproliferative primary cultures of rabbit cells may be converted to proliferative populations, and at least 3 serial passages achieved. In the presence of large concentrations of methotrexate (up to 1000 microgram/ml), epithelial cells in primary culture show no decrease in their ability to attach, spread, or keratinize. Following conversion to proliferative populations by trypsin and EDTA low concentrations of methotrexate (1 microgram/ml) are strongly cytotoxic. When the incorporation of 32PO4(3-) and 3H-thymidine into DNA of proliferative and nonproliferative cells is compared, the incorporation of 32PO4(3-), but not that of 3H-thymidine, correlates with changes in cell number and DNA content. In both primary and serially cultivated cells, L-serine is required for optimal growth.

Animals↗
PubMed1978

Isolation and growth of adult human epidermal keratinocytes in cell culture.

Human epidermal keratinocytes may be isolated in high yield from 0.1 mm keratotome sections of adult skin by short-term trypsin release. When plated on a collagen-coated plastic surface or on a collagen gel, keratinocytes attach with high efficiencies (greater than 70%) and form confluent, stratified cultures. Cell populations of predominantly basal cells produce proliferative primary cell cultures while populations of basal cells and malpighian cells result in nonproliferative primary cultures. Both nonproliferative and proliferative primary cultures may be subcultured on collagen gels following dispersion by trypsin and EDTA. Methotrexate strongly inhibits proliferative keratinocytes at low concentrations (0.1 microgram/ml) but has no cytotoxic effect on non-proliferative cells. L-serine and dexamethasone increase the multiplication rate of both primary and subcultured human keratinocytes.

Adult↗
PubMed1978

Growth hormone causes rapid induction of lactogenic receptor activity in the Snell dwarf mouse liver.

The Snell dwarf mouse (dw/dw) has no detectable PRL-binding sites in the microsomal fractions of its liver. Both bGH and bPRL, purified by preparative gel electrophoresis, induce PRL-binding sites when injected into dw/dw. Intraperitoneal injection of 100 micrograms bGH every 8 h results in the appearance of a high affinity PRL receptor 8--16 h after initiation of treatment. This induced binding capacity plateaus after 32 h of treatment and subsequently decreases to nondetectable levels 48 h after the last injection. [125I]Iodo-ovine PRL is displaced from the induced receptor equally well by similar concentrations of ovine PRL, human GH, and bovine PRL, but is displaced by bovine GH (bGH) only at approximately 100-fold higher concentrations. While untreated dw/dw livers do possess high affinity bGH-binding sites, treatment with bGH did not alter the bGH-binding activity. Treatment of dw/dw with cycloheximide does not prevent induction of PRL receptors by bGH injections. These observations indicate that bGH induces the PRL receptor by interacting with the cell at some point distal to the induced receptor site and does not require the synthesis of new proteins.

Animals↗
PubMed1978

Crosslinking of the nearest membrane protein neighbors in ATP depleted, calcium enriched and irreversibly sickled red cells.

ATP depleted or Ca2+ (0.1 mM) enriched normal red cells (greater than 80% echinocytes III) subjected to crosslinking by catalytic oxidation contain a greater than 1,000,000 daltons spectrin rich polymer cleavable by dithiothreitol (DTT) reduction. Similar complex is seen after glutaraldehyde crosslinking suggesting spectrin rearrangement into closer contacts or aggregation. In addition, a non-reducible greater than 1,000,000 daltons polymer is produced in fresh rbc or ghosts by high (greater than 0.5 mM) Ca2+ conc. and ionophore A23187. This complex is attributed to endogenous membrane protein crosslinking, catalyzed by a Ca2+ stimulated rbc transglutamidase. ISCs exhibiting a 4 fold increase in Ca2+ and a decrease in ATP do not exhibit these polymers. However, ISCs have an increased propensity to form the spectrin rich polymer during a subsequent ATP depletion and this is associated with a transformation of greater than 60% ISCs into spheroechinocytes. Similar cells are occasionally noted (greater than 4%) in the densest ISC rich fractions separated from fresh blood. We conclude that neither Ca2+, ATP dependent spectrin aggregation nor a spontaneous irreversible crosslinking underlie the membrane lesion of ISCs. Accelerated calcium gain and ATP depletion in ISCs leads to spectrin rearrangement and transformation of ISCs into spheroechinocytes which may represent an end stage ISC lesion resulting in an ISC removal from circulation.

Adenosine Triphosphate↗
PubMed1978

Metabolic dependence of protein arrangement in human erythrocyte membranes. I. Analysis of spectrin-rich complexes in ATP-depleted red cells.

The discocyte-echinocyte transformation and the decrease in deformability associated with red cell ATP depletion have been attributed to changes in the physical properties of spectrin and actin, membrane proteins located at the membrane-cytosol interface. We investigated the spontaneous formation of spectrin-rich complexes in human erythrocyte membranes, employing two-dimensional SDS-polyacrylamide gel electrophoresis. Membranes of red cells depleted in ATP under aerobic conditions exhibited (1) an increase in components 4.5 and 8 and globin subunits, (2) a spontaneous formation of heterodimers of spectrin 1 + 2 and spectrin 2 + component 4.9, and (3) a large molecular weight (greater than 10(6) daltons) protein complex with a high spectrin to band 3 ratio. These complexes were dissociated with dithiothreitol and were prevented by anaerobic incubation or the maintenance of red cell ATP and GSH levels with glucose, adenine, and inosine. The complexes 1 + 2 and 2 + 4.9 were also seen in acetylphenylhydrazine-treated, glucose-6-phosphate dehydrogenase-deficient fresh erythrocytes that showed marked GSH depletion but preserved greater than 70% of the original ATP level. However, membranes of these cells did not contain the greater 10(6) dalton aggregate with a high spectrin to band 3 ratio. We concluded that the formation of the latter complex results from rearrangement of spectrin and other polypeptides in membranes of ATP-depleted red cells. Under aerobic conditions, the rearranged proteins undergo spontaneous intermolecular crosslinkings through disulfide couplings.

Adenosine Triphosphate↗
PubMed1977

Partition of catalase and its peroxidase activities in human red cell membrane: effect of ATP depletion.

Partititon of catalase (hydrogen-peroxide:hydrogen-peroxide oxidoreductase EC 1.11.1.6) and peroxidase (donor:hydrogen-peroxide oxidoreductase EC 1.11.1.7) activities between the red cell membrane and the cytosol were studied under various experimental conditions. A small but significant amount of catalase (1.6%) was retained on human red cell membranes prepared by hemolysing washed red cells with 30 volumes of 10 mM Tris buffer, pH 7.4. Membrane -bound catalase had a relatively higher peroxidase activity than the soluble enzyme fraction. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate of the solubilized membranes demonstrated catalase to be a single band with a molecular weight of 60 000. Membranes prepared from adenosine triphosphate-depleted red cells depicted a two to three-fold increase in catalase activity, as well as an increase in 60 000 molecular weight band on polyacrylamide gel electrophoresis. The extra amount of retained catalase was a less efficient peroxidase than found in fresh membranes. The binding of catalase to ATP-depleted red cell membranes was dependent upon both pH and hemolysing ratio. Red cells incubated at pH 7.1 demonstrated a decrease in bound catalase, as did membranes prepared from red cells hemolysed at 1:100 dilution. beta-Mercaptoethanol decreased the catalase activity in the membranes and increased the odianisidine peroxidase activity without any significant effect on the 60 000-dalton band.

Adenosine Triphosphate↗
PubMed1977

Spontaneous, reversible protein cross-linking in the human erythrocyte membrane. Temperature and pH dependence.

Changes in pH significantly affect the morphology and physical properties of red cell membranes. We have explored the molecular basis for these phenomena by characterizing the pattern of protein disulfide cross-linkages formed spontaneously in ghost exposed to acid pH or elevated temperature (37 degrees C). Protein aggregation was analyzed by two-dimensional polyacrylamide gel electrophoresis in sodium dodecyl sulfate. incubation of ghosts at pH 4.0 to 5.5 (0-4 degrees C) yielded (i) complexes of spectrin and band 3, (ii) complexes of actin and band 3, (iii) band 3 complexes, i.e. dimer and trimer, and (iv) heterogeneous aggregates involving spectrin, band 3, band 4.2, and actin in varying proportions. Aggregation was maximal near the isoelectric points of the major membrane proteins, and appeared to reflect (i) the aggregation of intramembrane particles including band 3 and (ii) more intimate contact between spectrin-actin meshwork and band 3.

Actins↗
PubMed1977

Release of spectrin-free vesicles from human erythrocytes during ATP depletion. I. Characterization of spectrin-free vesicles.

Human erythrocytes incubated without glucose at 37 degrees C (in vitro aging) release spectrin-free vesicles after 12 or more hours. The release of vesicles is dependent upon ATP depletion. If the endogenous level of ATP is maintained, vesicle release is completely inhibited up to 54 h. Vesicle release is independent of hemolysis because in vitro aged cells and cells that maintain their ATP levels lose identical amounts of hemoglobin up to 45 h. 93 percent of all membrane particles released constitute a uniform population of spheres with a diameter of 185 +/- 23nm. These vesicles are of slightly varying densities due to varying contents of hemoglobin. Vesicles contain half the amount of membrane protein that is found in intact membranes when referred to the content of phospholipids phosphorus. This is primarily due to the absence of spectrin. However, their content of protein component III, glycophorin, and cholesterol remains the same as in intact membranes. Thus, the major integral membrane proteins are present in vesicles in similar quantities were surface area as in cells except for the enzyme acetylcholinesterase that is enriched up to twofold. The phospholipids composition of these vesicles is representative of the intact membrane except that the amount of phosphatidic acid is 10-fold higher and the amount of phosphatidylethanolamine is slightly lower than in erythrocytes. These results suggest a selective release of membrane domains that lack peripheral membrane proteins and are enriched in acetylcholinesterase. This release of spectrin-free vesicles from cells aged in vitro could represent an acceleration of the physiological aging process.

Acetylcholinesterase↗
PubMed1976

The coupling effects of some thiol and other sulfur-containing compounds on the circadian rhythm of cell division in photosynthetic mutants of Euglena.

Previous work has demonstrated a persisting, free-running, circadian rhythm of cell division in the P4ZUL photosynthetic mutant of the alga Euglena gracilis Klebs (Strain Z) Pringsheim grown organotrophically in continuous light or darkness at 19 degrees C following prior synchronization by a repetitive LD:10,14 light cycle. A similar circadian rhythmicity has been recently discovered in the W6ZHL heat-bleached and the Y9ZNalL naladixic acid-induced mutants of Euglena grown under comparable conditions. Over extended timespans, however, these mutants appear to gradually lose first their ability to display persisting overt rhythms, and then even their capability of being entrained by imposed LD cycles. These properties can be restored by the addition of certain sulfur-containing compounds to the medium including cysteine, methionine, dithiothreital, sodium monosulfide, sodium sulfite, and sodium thiosulfate, as well as thioglycolic [mercaptoacetic] acid. The implications of these findings toward biological clock mechanisms are discussed: It appears that some sort of coupling process is operating as opposed to the initiation of an underlying oscillation.

Amino Acids, Sulfur↗