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Biomedical subjects

R Marz

Publications and source records attributed to R Marz.

26 records · Page 2Linked to original sources
PubMed1977

Growth rate of cultured Novikoff rat hepatoma cells as a function of the rate of thymidine and hypoxanthine transport.

Novikoff rat hepatoma cells were propagated in suspension culture in the presence of 1 micron methotrexate and various concentrations of hypoxanthine (or adenosine plus guanosine) and thymidine and with or without the inhibitor of nucleoside and purine transport, Persantin (dipyridamole). Methotrexate-treated cells failed to replicate and died even if the medium was supplemented with either thymidine or a purine source, but normal replication occurred when both were present. The additional presence of Persantin reduced the rate of transport of thymidine or hypoxanthine and thus their incorporation into the nucleotide pool and decreased the rate of cell replication. The growth rate of the cells was directly proportional to the rate of incorporation of thymidine (in the presence of excess hypoxanthine) or of hypoxanthine (in the presence of excess thymidine) until the normal maximum growth rate was obtained. Normal cell replication in the presence of methotrexate and Persantin occurred only when the medium was supplemented with 500 micron hypoxanthine and 30 micron thymidine. The results illustrate a dependence of the growth rate of mammalian cells on the rate of transport of essential nutrients into the cell.

Adenosine↗
PubMed1977

G2+M arrest of cultured mammalian cells after incorporation of tritium-labeled nucleosides.

Novikoff rat hepatoma cells were propagated in suspension cultures containing 0.5 to 10 muC of 3H-methyl-thymidine, 3H-5-uridine, 3H-G-adenosine or 3H-8-adenine. The presence of the 3H-labeled precursors caused an inhibition of cell replication which was due to a delay or arrest of the cells in G2 and M. The degree of inhibition was proportional to the amount of radioactivity incorporated into nucleic acids. Almost immediate and complete inhibition resulted from incubation with 10 muC 3H-thymidine/ml. The presence of 0.5 muC 3H-thmidine/ml caused a significant increase in the relative proportion of cells in G2+M, even though the population doubling time of the culture appeared to be unaltered.

Adenine↗
PubMed1977

Relationship between thymidine transport and phosphorylation in Novikoff rat hepatoma cells as analyzed by a rapid sampling technique.

Incorporation of thymidine into Novikoff rat hepatoma cells was analyzed with a rapid sampling technique which allowed collection of 12 time points in 20 sec. Transport was a rapid, saturable, nonconcentrative process with a Km of about 85 micrometer. The intracellular thymidine pool was also rapidly labeled in cells which phosphorylated thymidine, that a group translocation process involving thymidine kinase can be ruled out. Under all conditions examined, phosphorylation, not the transport, of thymidine was the rate-determining step in its incorporation into the acid-soluble pool. Estimation of transport rates from total incorporation into cells which phosphorylate the substrate is invalid in this cell system and must be questioned in all instances.

Adenosine Triphosphate↗
PubMed1976

Transport and countertransport of thymidine in ATP depleted and thymidine kinase-deficient Novikoff rat hepatoma and mouse L cells: evidence of a high Km facilitated diffusion system with wide nucleoside specificity.

Incubation of cultured Novikoff rat hepatoma and mouse L cells in a glucose-free basal medium containing 5 mM KCN and 5 mM iodoacetate for about 10 minutes resulted in a complete depletion of the cells of ATP. ATP-depleted wild type cells or thymidine kinase-deficient sublines of Novikoff or L cells took up thymidine rapidly from the medium without concentrating it intracellularly, and exhibited countertransport of thymidine. Thus uptake was by facilitated diffusion. This transport system differs from the substrate-specific, low-Km (0.5 muM] thymidine transport system previously described for various types of cultured cells in that it exhibits an at least 100-fold higher Km and transports equally well various ribo- and deoxyribonucleosides. The results suggest that the rate-limiting step in thymidine incorporation into the nucleotide pool by wild type cells is phosphorylation rather than transport, or that the cells possess two transport systems, a facilitated diffusion system with low substrate specificity and a second system which involves substrate phosphorylation by thymidine kinase.

Adenosine Triphosphate↗
PubMed1976

The application of rapid kinetic techniques to the transport of thymidine and 3-O-Methylglucose into Mammalian cells in suspension culture.

Techniques are described by which the transport of nutrients into mammalian cells in suspension can be measured at intervals of 1.5 seconds. By application of these techniques, the existence of a saturable (Km = 85 muM), non-concentrative, transport system for thymidine was demonstrated in Novikoff rat hepatoma cells depleted of ATP. At concentrations of thymidine less than the Km, this system operated at velocities sufficient to nearly completely equilibrate intra- and extra-cellular thymidine pools within 8 seconds. In phosphorylating cells, the transport system operated with similar rapidity, so that intracellular phosphorylation was rate-limiting for the incorporation of thymidine into nucleotides. Uptake of 3-O-methylglucose occurred at comparable velocities, attaining 90% of equilibrium between internal and external pools within 25 seconds. Uptake of cytosine by simple diffusion was 100 times slower.

Animals↗