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Biomedical subjects

C Vinkler

Publications and source records attributed to C Vinkler.

8 recordsLinked to original sources
PubMed1999

Chorionic villus sampling in multiple pregnancies.

OBJECTIVE: To evaluate the accuracy and risk of chorionic villus sampling (CVS) for prenatal diagnosis in multiple pregnancies. METHOD: Twenty-eight chorionic villus samplings were carried out in a group of women with twin pregnancies. A transabdominal route was chosen in 24 samplings and the rest (four samplings) were carried out in a transcervical route. In the group of women with triple pregnancies, 14 tests were performed in a transabdominal route and one in a transcervical route. RESULTS: No sampling failure occurred. One laboratory failure occurred in a triplet pregnancy, and one abnormal karyotype (47,xy+18) was found in the group of 28 twin fetuses. The rest of the fetuses in this group had normal karyotypes. Of the five triplets, two chromosomal abnormalities were diagnosed: a mosaic 46,xy/47,xxy was found in both cases. One fetus was affected by fragile -x syndrome. Selective reduction of the affected fetuses was carried out. There was no spontaneous fetal loss. Fetuses which were found to have normal prenatal tests were also found to be normal when born. CONCLUSION: In this relatively small series of CVS in twins and triplets, the procedure has been proven to be safe and reliable for prenatal diagnosis.

Adult↗
PubMed1990

Stability of mixed micellar systems made by solubilizing phosphatidylcholine-cholesterol vesicles by bile salts.

Complete solubilization of phosphatidylcholine and cholesterol by bile salts in the form of stable mixed micelles requires that the effective ratio of bile salt/lipids in the mixed micelles (Re = ([bile salt] - critical micellar concentration)/([phosphatidylcholine] + [cholesterol]) will exceed a critical value. This equilibrium solubilizing ratio is an increasing function of the cholesterol/phosphatidylcholine ratio. In contrast, the concentration of sodium cholate required for solubilization of vesicles made of phosphatidylcholine and cholesterol does not increase by increasing the cholesterol/phosphatidylcholine ratio. Consequently, the latter solubilization procedure yields metastable mixed micelles whenever the cholate concentration is higher than that required for vesicle solubilization but lower than that needed for establishing a micellar equilibrium. These metastable mixed micelles undergo partial revesiculation to form cholesterol-rich vesicles that subsequently aggregate. Cholesterol crystallization appears to occur through its reorganization within these aggregated vesicles. The overall rate of the above series of processes increases sharply with the total lipid concentration and with the cholesterol/phosphatidylcholine ratio. The dependence of the rate on the effective ratio of bile salts/lipids is very complex: at any given ratio of cholesterol/phosphatidylcholine within the range of 0.3 to 0.5, increasing the cholesterol/phosphatidylcholine ratio requires higher cholate concentrations for the formation of stable mixed micelles (higher equilibrium solubilizing ratio). On the other hand, the metastable mixed micellar larsystems are long-lived whenever the effective ratio of cholate/lipids is lower than a critical value.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile Acids and Salts↗
PubMed1988

Interaction of furosemide with lipid membranes.

The interaction of furosemide with different phospholipids was investigated. Its influence on the lipid structure was inferred from its effect on the phase transition properties of lipids and on the conductance of planar bilayer membranes. The thermotropic properties of dipalmitoyl phosphatidylcholine, phosphatidylethanolamine (natural), dipalmitoyl phosphatidylethanolamine, brain sphingomyelin, brain cerebrosides and phosphatidylserine in the presence and absence of furosemide were investigated by differential scanning calorimetry. The modifying effect of furosemide seems to be strongest on phosphatidylethanolamine (natural) and sphingomyelin bilayers. The propensity of furosemide to decrease the electrical resistance of planar lipid membranes was also studied and it is shown that the drug facilitates the transport of ions. Partition coefficients of furosemide between lipid bilayers and water were measured.

Cerebrosides↗
PubMed1988

Stability of mixed micellar bile models supersaturated with cholesterol.

The maximal equilibrium solubility of cholesterol in mixtures of phosphatidylcholine (PC)1 and bile salts depends on the cholesterol/PC ratio (Rc) and on the effective ratio (Re) between nonmonomeric bile salts and the sum (CT) of PC and cholesterol concentrations (Carey and Small, 1978; Lichtenberg et al., 1984). By contrast, the concentration of bile salts required for solubilization of liposomes made of PC and cholesterol does not depend on Rc (Lichtenberg et al., 1984 and 1988). Thus, for Rc greater than 0.4, solubilization of the PC-cholesterol liposomes yields PC-cholesterol-bile salts mixed micellar systems which are supersaturated with cholesterol. In these metastable systems, the mixed micelles spontaneously undergo partial revesiculation followed by crystallization of cholesterol. The rate of the latter processes depends upon Rc, Re, and CT. For any given Rc and Re, the rate of revesiculation increases dramatically with increasing the lipid concentration CT, reflecting the involvement of many mixed micelles in the formation of each vesicle. The rate also increases, for any given CT and Re, upon increasing the cholesterol to PC ratio, Rc, probably due to the increasing degree of supersaturation. Increasing the cholate to lipid effective ratio, Re, by elevation of cholate concentration at constant Rc and CT has a complex effect on the rate of the revesiculation process. As expected, cholate concentration higher than that required for complete solubilization at equilibrium yields stable mixed micellar systems which do not undergo revesiculation, but for lower cholate concentrations decreasing the degree of supersaturation (by increasing [cholate]) results in faster revesiculation. We interpret these results in terms of the structure of the mixed micelles; micelles with two or more PC molecules per one molecule of cholesterol are relatively stable but increasing the bile salt concentration may cause dissociation of such 1:2 cholesterol:PC complexes, hence reducing the stability of the mixed micellar dispersions. The instability of PC-cholesterol-cholate mixed systems with intermediary range of cholate to lipids ratio may be significant to gallbladder stone formation as: (a) biliary bile contains PC-cholesterol vesicles which may be, at least partially, solubilized by bile salts during the process of bile concentration in the gallbladder, resulting in mixtures similar to our model systems; and (b) the bile composition of cholesterol gallstone patients is within an intermediary range of bile salts to lipids ratio.

Cholesterol↗
PubMed1980

Effects of permeant buffers on the initial time course of photophosphorylation and postillumination phosphorylation.

Permeant buffers (pyridine, imidazole, or phosphate) caused similar increases in the time required for onset of ATP synthesis in the light in the presence of valinomycin and K+; and in the illumination time required for postillumination phosphorylation with or without or without valinomycin and K+. Based on prior evidence, the minimum illumination time required for postillumination phosphorylation in thylakoid membranes is taken as a measure of the time required for formation of a transmembrane pH gradient sufficient to drive ATP synthesis. Our results are consistent with the view that, following illumination, as the transient transmembrane electric gradient decays, the establishment and maintenance of a pH gradient serves for energy transfer from the photosystems to the ATP synthase complex.

Buffers↗
PubMed1978

Light-driven ATP formation from 32Pi by chloroplast thylakoids without detectable labeling of ADP, as measured by rapid mixing and acid quench techniques.

The labeling of ATP and ADP in the first few milliseconds of exposure of chloroplast thylakoids to light, 32Pi, and ADP has been measured. At least 4 mol of ATP/mol of coupling factor 1 (CF1)-ATPase can be formed without detectable labeling of membrane-bound or free ADP. Such results are consistent with ADP and not AMP as the primary acceptor of Pi in photophosphorylation. Evidence is presented demonstrating that quenching with perchloric acid, as used in these and earlier experiments, is satisfactory for the measurement of the amount and nature of membrane-bound nucleotides.

Adenosine Diphosphate↗