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Biomedical subjects

W Li

Publications and source records attributed to W Li.

At least 1,369 records · Page 76Linked to original sources
PubMed1986

Elasticity of synthetic phospholipid vesicles and submitochondrial particles during osmotic swelling.

A rapid and accurate method has been developed for measuring the elastic response of vesicle bilayer membranes to an applied osmotic pressure. The technique of dynamic light scattering is used to measure both the elastic constant and the elastic limit of dioleoylphosphatidic acid (DOPA) and DOPA-cholesterol vesicles and of submitochondrial particles derived from the inner membrane of bovine heart mitochondria. The vesicles prepared by the pH-adjustment method are unilamellar and of uniform size between 240 and 460 nm in diameter. The vesicles swell uniformly upon dilution. The observed change in size is not due to any change in the shape of the vesicles. The data also indicate that the vesicles are spherical and not flaccid. The total vesicle swelling in these studies resulted in a 3-4% increase in surface area for vesicles swollen in 0.15 M KCl and a 5-10% increase in surface area for vesicles swollen in 0.25 M sucrose. This maximum represents the elastic limit of the vesicles. Evidence is presented to show that the vesicles release contents after swelling to this maximum, reseal immediately, and reswell according to the osmotic pressure. For DOPA vesicles in a 0.15 M KCl-tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) buffer (pH 7.55), the observed membrane modulus is found to be in the range of 10(8) dyn/cm2. The modulus was found to be in the order of 10(7) dyn/cm2 for DOPA vesicles in a 0.25 M sucrose-Tris-HCl buffer (pH 7.55). This is comparable to that of submitochondrial particles in the same sucrose-Tris-HCl buffer. The observed membrane modulus also decreases with vesicle size. Its magnitude and its variation with ionic strength indicate that the major component of bilayer elasticity is neither the inherent elasticity of the bilayer nor the bending modulus. The variation of the membrane modulus with respect to curvature suggests that its principal component may be related to surface tension effects including the negative charges on the vesicle surface. There is considerable variation between vesicles swollen in sucrose and those swollen in KCl in the membrane modulus, in the elastic limit at which the vesicles burst, and in the transbilayer pressure difference at bursting. The latter was found to be 4-6 mosM (10(5) dyn/cm2) in sucrose solution and 20-4 mosM (10(6) dyn/cm2) in KCl solution.

Animals↗
PubMed1986

Uniform preparations of large unilamellar vesicles containing anionic lipids.

A general procedure for the preparation of large unilamellar vesicles of selected sizes has been developed. The procedure consists of dissolving the lipid in organic solvent, washing with mild acid, removing the solvent, adding salt (0.15 M KCl) solution, and adjusting the pH (raising it to about pH 10 and lowering it immediately to pH 7.55). The procedure takes less than 30 min. The resulting unilamellar vesicles are of a single size with a rather low standard deviation. The sizes of these preparations range between 150 and 1000 nm in diameter. Sizes and polydispersities were measured to within 1-2% by photon correlation spectroscopy. Vesicle size varies with the phospholipid structure, the composition of the phospholipid mixture, the ionic strength of the medium, the alkyl chain composition, the cholesterol content of the phospholipid mixture, and the timing of the pH adjustment procedure. Uniform preparations of vesicles have been obtained from the dioleoyl esters of phosphatidic acid, phosphatidylglycerol, phosphatidylethanolamine, and phosphatidylserine, from diphytanyl ethers of glycolipid sulfate, phosphatidylglycerol, phosphatidylglycerol phosphate, and phosphatidylglycerol sulfate, from bovine liver phosphatidylinositol, from Escherichia coli phosphatidylethanolamine, from membrane lipid extracts from E. coli and Holabacterium cutirubrum, and from dodecanesulfonate-alkanol mixtures and free oleic acid. The preparation of unilamellar vesicles from oleic acid is novel, and the size range is 600-3000 nm; the preparations are relatively uniform. Vesicles of phospholipids in which sucrose and trehalose replace salt as the impermeant do not differ significantly from those prepared in pentaerythritol.

Escherichia coli↗
PubMed1986

Influence of passive smoking on admissions for respiratory illness in early childhood.

An association was sought between passive smoking and inpatient admissions for respiratory illness in 1058 children born between 1 June and 31 December 1981 and living in the neighborhoods of Nan-Jing Western Road and Yan-An Western Road in Jing-An District, Shanghai. The admission rate for first episodes of respiratory illness was positively correlated with the total daily cigarette consumption of family members during the children's first 18 months of life. The relative risk of developing a first episode of respiratory illness was 1.80 for children living in families including people who smoked 10 or more cigarettes a day compared with those living in non-smoking families. Multiple logistic regression analysis showed that the effect of passive smoking on inpatient admission for respiratory illness was independent of the child's birth weight, type of feeding, father's education, size of the home, and chronic respiratory disease among adults in the family. The adjusted odds ratios compared with the non-smoking group were 1.17 in families smoking 1.9 cigarettes daily and 1.89 in families smoking 10 or more cigarettes daily. These data suggest that exposure to household cigarette smoke of children in early life increases the risk of severe respiratory illness.

China↗
PubMed1986

Non-competitive inhibition of myo-inositol transport in cultured bovine retinal capillary pericytes by glucose and reversal by Sorbinil.

myo-Inositol transport by retinal capillary pericytes in culture was characterized. The major myo-inositol transport process was sodium-dependent, ouabain-sensitive, and saturable at 40 mM, indicating a carrier-mediated process. The sodium ion concentration required to produce one-half the maximal rate of myo-inositol uptake ([Na+]0.5) did not show dependence on the external myo-inositol concentration (22.3 mM sodium for 0.005 mM myo-inositol; 18.2 mM sodium for 0.05 mM myo-inositol). myo-Inositol transport was an energy-dependent, active process functioning against a myo-inositol concentration gradient. The kinetics of the sodium-dependent system fitted a 'velocity type' co-transport model where binding of sodium ion to the carrier increased the velocity (Vmax 28 to 313 pmol myo-inositol/micrograms DNA per 20 min when [Na+] varied from 9 to 150 mM) but not the affinity for myo-inositol (Km 0.92 to 0.83 mM when [Na+] varied from 9 to 150 mM). Metabolizable hexoses (D-glucose or D-galactose; greater than 5 mM) inhibited myo-inositol uptake. Dixon-plot analysis indicated that the inhibition was non-competitive with a Ki of 22.7 mM for D-glucose and 72.6 mM for D-galactose. The inhibition was significantly reversed by Sorbinil (0.1 mM), an aldose reductase inhibitor. In contrast, high concentrations of non-metabolizable hexoses (L-glucose, 3-O-methyl-D-glucose), or partially metabolizable 2-deoxy-D-glucose, did not significantly inhibit myo-inositol uptake. The inhibitory effect of D-glucose or D-galactose on myo-inositol transport appeared to be related to glucose or galactose metabolism via the polyol pathway.

3-O-Methylglucose↗
PubMed1986

Monoclonal antibody detection of transformation associated protein (TAP) in ts110 Moloney murine sarcoma virus transformed 6M2 cells that are different from the mos gene product.

By the use of a highly specific monoclonal antibody (designated MC), we were able to detect three radiolabeled bands with molecular weights of 60,000, 63,000, and 66,000 daltons in the ts-110 Moloney murine sarcoma virus mutant-transformed rat kidney cells known as 6M2. Expression of transformation properties as well as these three bands in 6M2 cells was found to be temperature sensitive. Therefore, MC detected factors that are apparently associated with the transformation of 6M2 cells. These factors are tentatively referred to as transformation associated proteins. These transformation proteins were found in two other Moloney murine sarcoma virus-transformed rat cell lines. These proteins were found to differ from known gene products of the ts-110 Moloney murine sarcoma virus mutant and do not have kinase activity. The transformation associated proteins may represent rat cellular factors activated during the transformation of rat cells by Moloney murine sarcoma virus.

Animals↗
PubMed1986

Ascorbate regeneration in bovine ocular tissues by NADH-dependent semidehydroascorbate reductase.

Despite its fast autoxidation in vitro, ascorbate remains in its reduced form in vivo, indicating a special mechanism may be involved in its regeneration. The presence of an NADH-dependent reductase system, semidehydroascorbate reductase (SDR), for regeneration of ascorbate from its partially oxidized form, semidehydroascorbate (SDA), was demonstrated in bovine ocular tissues after extraction in Triton X-100. Highest SDR activity was detected in retinal extracts in the order of retina greater than pigment epithelium-choroid = ciliary body greater than iris. Minimal or no activity was observed in lens extracts or in aqueous fluid. Freezing and thawing, or boiling, destroyed the NADH-dependent SDR activity. NADH oxidation was significantly reduced (22% of total activity) when assays with retinal extracts were performed at 5 degrees C. Treatment with 4 mM, N-ethylmaleimide reduced the rate of NADH oxidation to 73 or 42% compared with control values with retinal or ciliary body extracts, respectively.

Animals↗
PubMed1985

Preparation and characterization of monodisperse unilamellar phospholipid vesicles with selected diameters of from 300 to 600 nm.

A method has been developed for making large unilamellar vesicles (LUV) with low polydispersity. The LUV, constituted of dioleoylphosphatidic acid (DOPA), 300 nm in diameter are made by a modification of the pH adjustment technique (Hauser, H. and Gains, N. (1982) Proc. Natl. Acad. Sci. USA 79, 1683-1687). This size is 10 times that (30 nm) of vesicles prepared by prolonged sonication. Vesicle size is increased stepwise by adding cholesterol (to a maximum of 40 mol% cholesterol) to form vesicles in 0.15 M KCl with up to 600 nm diameter. The vesicle size is measured by photon correlation spectroscopy, electron microscopy, and by measurement of the internal volume with cyanocobalamin while calculating the number of DOPA molecules per vesicle. Vesicles are stable for at least three weeks. Sepharose 4B column chromatography of the preparation yields a peak of fractions with the same polydispersity as the original sample and shows that 30 to 40% of the original lipid in a sample is recovered as LUV. Less than 2% of the sample forms small unilamellar vesicles (SUV) (diameter = 30 nm), which emerge from the column in a separate peak. Since the remaining lipid is not suspended in the buffer during vesicle formation, for most purposes the vesicles may be used immediately after titration so that they can be prepared in less than 40 min.

Hydrogen-Ion Concentration↗