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Biomedical subjects

J K Thomas

Publications and source records attributed to J K Thomas.

14 recordsLinked to original sources
PubMed1985

Effects of nitrogen mustard on potassium transport systems and membrane structure of Ehrlich ascites tumor cells.

By Ehrlich ascites tumor cells 86Rb+ has been shown to be a suitable tracer for K+-transport. Sixty percent of the total 86Rb-uptake into these cells is ouabain-inhibitable, 30% is sensitive to furosemide and 10% enters the cells by ouabain and furosemide-insensitive systems. N-Mustard inhibits both the ouabain-sensitive and the furosemide-inhibitable systems. The uptake which is resistant to both inhibitors is not affected by the alkylating drug. At N-mustard concentrations below 10 microM, the reduction of the Rb-uptake is predominantly due to the inhibition of the furosemide-sensitive transport. Higher concentrations are required before a significant inhibition of the ouabain-sensitive transport can be observed. The dose response curve of the furosemide-sensitive transport--not, however, of the ouabain inhibitable pump--corresponds to the dose response curve for the antiproliferative activity of N-mustard. The recovery of the furosemide-sensitive transport after a single exposure to N-mustard is relatively slow and--in contrast to the repair of DNA cross-links--is characterized by an initial 4-hr lag period. Furosemide alone does not interfere with cell multiplication. The inhibition of the transport system alone does, therefore, not explain the antitumor activity of N-mustard. The effect is discussed as a marker for membrane lesions after exposure to alkylating agents. In order to investigate the influence of N-mustard on membrane structure, membranes were labelled with diiodofluoresceiniodoacetamide. Anisotropy curves obtained from time-dependent depolarization of delayed fluorescence indicated a mustard induced immobilization of membrane constituents. Lateral diffusion of lipophilic probes was determined by following the quenching of fluorescence of pyrene by cetylpyridinium. The latter studies yielded no evidence for a change in membrane lipid fluidity. The data are interpreted as the results of cross-links of membrane proteins by the bifunctional alkylating agent.

Animals↗
PubMed1979

Comparative studies of the physical state of the lipid phase of normal and hypercholesterolemic very low density lipoprotein.

Very low density lipoproteins (VLDL) were prepared from the serum of rabbits at various stages of hypercholesterolemia (95--1665 mg cholesterol/100 ml of serum). The most notable chemical change in hypercholesterolemic (hc) VLDL was the greatly increased content of cholesteryl esters and the greatly decreased content of triglycerides, compared to normal (n) VLDL. Structurally, the lipid region of n VLDL possessed a much lower microviscosity than did hc VLDL, when analyzed by fluorescence polarization and pyrene eximer methods. The microviscosity of the redispersed n VLDL lipid extract was considerably greater than the observed in n VLDL; but less than that of hc VLDL. Incorporation of pyrene into the lipid region of n VLDL and hc VLDL allowed assessment of various properties of the surface and hydrocarbon regions of these lipoproteins. Only slight differences were found in the pyrene monomer 3 : 1 fluorescence emission peak ratios, and in the rate constant for quenching of pyrene by O2. However, the quenching rate constant of pyrene by I- and iodoheptane were different for each lipoprotein.

Animals↗
PubMed1976

The study of rous sarcoma virus-transformed baby hamster kidney cells using fluorescent probes.

The fluorescent probes pyrene, pyrene butyric acid and N-phenyl 1-naphthylamine have been used to investigate the changes that accompany in vitro transformation of a baby hamster kidney cell line using Rous sarcoma virus. The fluorescent probes which reside in the membrane were used to compare the changes in microviscosity and polarity of the membranes of normal cells with two transformed cell lines. The spectrofluorimetric data indicate that following transformation the probe N-phenyl 1-naphthylamine resides in a more polar environment. However, using the probe pyrene, the yield of excimer indicates decreased mobility of this probe in the membrane of transformed cells. The data also indicate differences between the two transformed cell lines. Laser photolysis was used to study the lifetime of the pyrene probes and the quenching of the pyrene fluorescence in the membrane by several different quenching molecules. The data indicate differences between the three cell lines and suggest that transformation decreases movement within the membrane.

1-Naphthylamine↗
PubMed1976

Kinetic processes in Escherichia coli membranes and cells. A laser photolysis study using derivatives of pyrene.

Pyrene and several derivatives of pyrene are used to investigate photo-induced kinetic processes in whole cells and membranes extracted from Escherichia coli. A mutant of E. coli was used which, under appropriate growth conditions, produced a complete or incomplete lipopolysaccharide in the outer membrane. The pyrene derivatives used were: pyrene sulfonic acid, pyrene butyric acid and the ester of pyrene butyric acid and 10-hydroxydecanoic acid. The pyrene chromophore was excited by the ultraviolet pulse from a Q switch, frequency-doubled, ruby laser. The lifetimes of the pyrene fluorescence in the presence of the quenchers O2, thallous ion (T1+), I-and CH3NO2 were measured and tabulated as second order rate constants. For the most part the quenching rate constants were much lower than the corresponding values observed in simple nonviscous solution, e.g. ethanol. This is interpreted as being due to the location of the probe within the membrane. The membrane inhibits the movement of the quenchers to the excited state. Cell membranes containing complete lipopolysaccharide showed significantly lower quenching rates for the probes pyrene and pyrene sulfonic acid than cell membranes with incomplete lipopolysaccharide. From an amalysis of the kinetic data it is suggested that pyrene and pyrene sulfonic acid are located near and under lipopolysaccharide and close to membrane proteins. On the other hand, no effect of lipopolysaccharide composition was observed for the probes pyrene butyric acid and pyrene butyroyl decanoic acid. This may suggest that these probes are located primarily in the lipid part of the membrane. A simple model for the outer membrane of E. coli is suggested that accounts for the observed laser-induced kinetic processes.

Biological Transport↗
PubMed1976

Effect ofcholinergic ligands on the lipids of acetylcholine receptor-rich membrane preparations from Torpedo californica.

Ion permeation, triggered by ligand-receptor interaction, is associated with the primary events of membrane depolarization at the neuromuscular junction and synaptic connections. To explore the possible sites of ion permeation, the long-lived fluorescent probe pyrene (fluorescence lifetime approximately 400 nsec) has been inserted into the lipid phase of acetylcholine receptor-rich membrane (AcChR-M) preparations from Torpedo californica. The pyrene probe is susceptible to both fluidity and permeability changes in the lipid bilayer. These changes are detected by variations in the rate of decay of the excited singlet state of pyrene after pulsation with a 10-nsec ruby laser flash. Variations of these lifetimes in the membrane preparations alone or in the presence of quenchers show that binding of cholinergic agonists and antagonists, neurotoxins, and local anesthetics to AcChR-M produces varying effects on the properties of the pyrene probe in the lipid phase. It is concluded that binding of cholinergic ligands to the receptor does not significantly alter the fluidity of permeability of the lipids in the bilayer contact with pyrene. On the other hand, local anesthetics do affect these properties.

Acetylcholine↗