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J K Thomas

Publications and source records attributed to J K Thomas.

35 records · Page 2Linked to original sources
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↗
PubMedDate not supplied

CT in the posttraumatic liver.

A case is presented which demonstrates the ability of CT to be of use in an unusual presentation of a not uncommon problem, i.e. hepatic hematoma following laceration and repair in a posttraumatic setting. Subsequent compromise of the portal venous system and the inferior vena cava in its retrohepatic course, and resultant abdominal findings are demonstrated and discussed.

Adult↗
PubMedDate not supplied

Apparent hemolysis in an AIDS patient receiving trimethoprim/sulfamethoxazole: case report and literature review.

OBJECTIVE: To describe a case of acute hemolysis associated temporally with administration of trimethoprim/sulfamethoxazole (TMP/SMX) in a patient with AIDS, review the available literature on TMP/SMX-induced hemolytic anemia, and discuss possible drug- and disease-related factors that may have contributed to the episode of hemolysis. CASE SUMMARY: A precipitous decrease in red blood cell count, hemoglobin, and hematocrit occurred shortly after a black woman with AIDS received a single intravenous dose of TMP/SMX for Pneumocystis carinii pneumonia. Following drug discontinuation and repeated transfusions, the patient's hematologic indices returned to baseline. LITERATURE SOURCES: References were obtained using MEDLINE searches, the bibliographies of articles identified during the searches, review articles, and standard textbooks. DATA SYNTHESIS: Of the two different mechanisms of TMP/SMX-induced hemolytic anemia, the reaction is most likely to occur via dose-related oxidative disruption of the erythrocyte membrane in subpopulations deficient in glucose-6-phosphate dehydrogenase (G6PD) activity. In the US, G6PD deficiency most frequently is encountered among blacks. The potential for hemolysis may be further increased in G6PD-deficient AIDS patients, who also appear to lack adequate intracellular glutathione, which is essential for protecting the erythrocyte membrane from oxidative damage. Although an assay for G6PD activity was not conducted, the case circumstances were consistent with TMP/SMX-induced hemolysis in a G6PD-deficient patient. CONCLUSIONS: Black patients with AIDS who are receiving relatively high (greater than or equal to 50 mg/kg/d) dosages of TMP/SMX should be monitored closely for signs and symptoms of hemolytic anemia.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

The laser two-photon photolysis of liquid carbon tetrachloride.

The two-photon photolysis of liquid CCl4 with 25 ps pulses of 266 nm light has been studied and compared with similar studies with high energy radiation. Both neutral and ionic species are produced from excited states and ionization. The emphasis of the study is on the ionic processes, while some data related to excited states and free radicals are presented. In both radiolysis and photolysis, a solvent separated charged pair, CCl3+ // Cl-, exhibiting a lambda(max) at 475 nm, is observed that exhibits a total growth over 38 to 100 ps. Solutes with ionization potentials less than that of CCl4 (11.47 eV) reduce the yield of the 475 nm species producing radical cations of the solute. The efficiency of this process is about 10-fold larger in radiolysis compared with photolysis. Analysis of the data suggest that the lower energy of two-photon photolysis produces a charge pair CCl4+ // CCl4-, which decays in about 3 ps to CCl4+ // Cl-. This species then decays to CCl3+ // Cl-. The lifetime of the growth of the 475 nm is measured as 46 ps. These studies clearly show areas where radiolysis and photolysis can be quite similar and also areas where the vast difference in excitation energy introduces stark differences in the observed radiation and photoinduced chemistry.

Carbon Tetrachloride↗