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Biomedical subjects

E M Kosower

Publications and source records attributed to E M Kosower.

At least 55 records · Page 3Linked to original sources
PubMed1977

Sensitivity of hemoglobin thiol groups within red blood cells of rat during oxidation of glutathione.

The intracellular thiol-oxidising diazenes, diazenedicarboxylic acid bis-N,N-dimethylamide and diazenedicarboxylic acid bis-N'-ethylpiperazinide, have been used in the study of red cells. A difference in the consequences of diazene oxidant treatment between the human red cell and rat red cells has been found in respect to the quantity of oxidant needed for glutathione (GSH) oxidation, to the fate of GSH, and to the reactivity of hemoglobin. In the first place, significantly more oxidant is needed for GSH oxidation in the rat red cell than in the human cell. Secondly, in the human cell, all of the GSH is converted to glutathione disulfide (GSSG), from which GSH is regenerated. In the rat cell, GSH disappears without being converted to GSSG, and GSH is not regenerated. Thirdly, a decrease in rat hemoglobin thiol groups, but no change in human hemoglobin, is found. Sterically unhindered thiol groups in the rat hemoglobin are thought to react with the usual adduct intermediate in GSH oxidation by diazene (formed from RCON = NCOR + GSH leads to RCON(SG)NHCOR) to produce mixed disulfides, from which GSH is not easily regenerated. The results support the idea that reduction of mixed disulfides of GSH and protein is not carried out directly by GSSG reductase but necessitates thiol transferase and GSH. The thiol-oxidising diazenes may be of use in mapping of exposed, reactive thiol groups in proteins.

Animals↗
PubMed1977

Inhibition of cytokinesis in Friend leukemia cells by membrane mobility agents.

Treatment of a line of Friend leukemia cells with a dispersion of the membrane mobility agent, A2C, yields cells that undergo successive nuclear divisions without cytokinesis, resulting eventually in cells with as many as 30 nuclei. Neither the DNA replication rate of the cells nor the generation time is different after treatment; in addition, the multiple nuclei divide synchronously, and the chromosome number corresponds to the number of nuclei in the cell. Inhibition of cytokinesis is not observed if the cells are washed with reagent-free medium within 1 hr of treatment, but is observed if washing is delayed for 24 hr. Membrane mobility agent loaded with the fluorescent probe, Flomol F20C, leads to fluorescent membrane; fluorescence disappears from the membrane after a change of medium within 1 hr, but not after a change of medium within 24 hr. Some stages in the overall development resemble those seen for cytochalasin B inhibition of cytokinesis, although the mechanisms may well be different for the inhibition promoted by membrane mobility agent. The inhibition of cytokinesis by A2C provides a potentially interesting means of studying cytokinesis and the regulation of differentiation.

Animals↗
PubMed1976

The thiol-oxidizing agent diamide increases transmitter release by decreasing calcium requirements for neuromuscular transmission in the frog.

Diamide, which in concentrations of 10(-5) M and higher oxidizes glutathione intracellularly, produces a dose-related increase in the frequency of miniature end-plate potentials (MEPPs). With high enough doses, quantal release is blocked, apparently through exhaustion. The early phase of MEPP frequency increase is accompanied by an increase in EPP amplitude that may reach more than 10-fold and is therefore not produced by depolarization of axon terminals. Subsequently, EPP amplitude is reduced and falls to zero, associated with failure of invasion of the nerve action into the terminals while the MEPP frequency remains elevated. Both facilitation and PTP follow the time course of change in EPP amplitude. The increase in MEPP frequency with diamide does not require external Ca2+ but raising external Ca2+ increases the MEPP rate in the presence of diamide. External Ca2+ is necessary for EPP appearance and also potentiates the diamide effects. Conversely diamide reduces the requirements for Ca2+ in releasing ACh. Diamide substitutes for external Ca2+ in K+ evoked MEPP release and in the absence of external Ca2+, diamide-evoked MEPP release is increased by raising external Mg2+ levels. The action of diamide may be dependent on the actual release of Ca2+ from intracellular stores or it may work through mimicking some of the actions of Ca2+. The action of diamide bears close resemblance to the effects of prolonged stimulation of the motor axon at 10 Hz.

Acetylcholine↗
PubMed1976

Diamide acts intracellularly to enhance transmitter release: the differential permeation of diamide, DIP, DIP+1 and DIP+2 across the nerve terminal membrane.

The actions of the new potent thiol oxidizing agents, diazene dicarboxylic acid bis (N'-methyl piperazide) (DIP) and the N'-methyl iodide (DIP + 1) and the bis-N'-methyl iodide (DIP + 2) salts of DIP, were tested at the frog neuromuscular junction. At 20 degrees C, DIP was as fast as the thiol oxidizing agent, diamide, in evoking transmitter release but was appreciably less effective at 6 degrees C. DIP + 1 and DIP + 2 did not increase transmitter release. Since the three agents are potent oxidizers of glutathione and since the effectiveness of the compounds appears to depend on their ability to exist, at least in part, in a neutral form at physiological pH, it is concluded that their action as promoters of transmitter release depends on their ability to permeate nerve terminal membranes. Thus, both diamide and DIP act to increase transmitter release by the intracellular oxidation of glutathione. The two charged agents, DIP + 1 and DIP + 2, are potent muscular depolarizing agents. It is probable that the quaternary nitrogen groups of these compounds render them cholinomimetics.

Acetylcholine↗
PubMed1975

DIP and DIP+2 as glutathione oxidants and radiation sensitizers in cultured Chinese hamster cells.

Two diamide analogues, diazene dicarboxylic acid bis (n'-methylpiperazide) or DIP, and its bis-N'-methyl iodide salt, or DIP + 2, were tested for their ability to penetrate cultured Chinese hamster cells and oxidize intracellular glutathione. DIP penetrated the cells at a reasonable rate at 18 degrees C, 160 nmoles being required to oxidize the endogenous glutathione of 2 X 10(6) cells, but it penetrated very slowly at 0 degrees C. DIP +2 did not effectively oxidize glutathione in Chinese hamster cells, possibly because it did not enter the cells. DIP became toxic after about 10 min of exposure, but its toxicity could be moderated by using anoxic conditions. DIP, but not DIP +2, sensitized anoxic Chinese hamster cells to X-radiation by a factor of 1-5, an effect that was due entirely to removal of the shoulder from the survival curve.

Azo Compounds↗
PubMed1972

A molecular basis for learning and memory.

Three stages in memory (electrical, short-term and long-term) are reviewed. The short computing time of organized neural systems favors synapses as loci for storage of memory. Transfer of neuronal excitation depends upon transfer of transmitter, involving the steps: vesicle attachment to presynaptic vesicle-release sites, contraction at dithiolate structures of these sites, exocytosis of transmitter, movement of transmitter across synaptic cleft, and reception at postsynaptic sites. Disulfide formation from dithiolates (calcium dithiolate salt) occurs during excitation and can represent a short-term alteration in properties of vesicle-release sites and, thus, short-term memory. Repair by one mechanism of the altered vesicle-release sites through reduction of the disulfide bond returns the system to its original state or, by a second mechanism, enlarges the presynaptic area covered by these sites. Such enlargement is a stable, permanent mode: long-term memory. Suitable concentrations of transmitter at postsynaptic receptor sites lead to mobilization of additional receptor sites through polymerization of monomeric receptor units. Postsynaptic expansion constitutes a metastable long-term storage, readily reconstituted under appropriate stimuli. Reverberations at the electrical stage of memory are suggested as a necessary link to the chemical stage of memory. These ideas constitute the elements of a molecular theory of learning and memory.

Acetylcholine↗