The 'transition probability model' and the regulation of proliferation of human diploid cell cultures during aging.

Genealogies derived from time-lapse cinemicrophotographic studies of aging human diploid cell cultures were analysed in terms of the 'transition probability' model. It was found that the distribution of intermitotic times obtained from middle passage cells deviated only slightly from that predicted by the model. In contrast, the plot for late passage cultures did not fit the predicted pattern and appeared to be composed of multiple curves. These changes are discussed in reference to cellular senescence as expressed by normal human diploid cells in vitro.     

Initial characterization of a HTC cell variant partially resistant to the anti-proliferative effect of ornithine decarboxylase inhibitors

Under the selective pressure of -α-methylornithine (α-MeOrn), a competitive inhibitor of ornithine decarboxylase (ODC) (EC 4.1.1.17) a clone of rat hepatoma tissue culture (HTC) cells has been isolated and designated HMO_A. The growth of this clone is affected by the drug only after a lag period of three generations. The same partial resistance was observed to -α-difluoromethyl ornithine (α-DFMeOrn), an irreversible inhibitor of ODC. HMO_A cells showed elevated ODC activity with a concomitant increase of the putrescine content but no change in S-adenosyl- -methionine decarboxylase (SAM-DC) (EC 4.1.1.50) activity. Evidence is given that this overproduction of putrescine may be responsible for the partial resistance of HMO_A cells to the anti-proliferative effect of the ODC inhibitors. α-MeOrn increases ODC and SAM-DC activities and α-DFMeOrn raises SAM-DC activity in a time and cell line-dependent manner. These findings may support the concept that intracellular putrescine and spermidine play a direct or indirect regulatory role in the expression of ODC and SAM-DC. Thus, the variant cell should be useful for studies on the genetic regulation of polyamine metabolism in eukaryotic cell systems.     

Scintillation fluid shortens exposure times in autoradiography

Premixed, commercially available scintillation fluids were used to reduce exposure time of tritium (3H) and iodine-125 (125I)-labeled whole cells, and of 3H-labeled Giemsa-banded chromosome preparations. Emulsion-coated slides were dipped into scintillator for no longer than 2 min and exposed in the dark at 4 degrees C. Maximal values for percentage of human diploid cell (WI-38) nuclei labeled with 3H-thymidine of moderate specific activity were obtained in 12 hr. Without scintillator the exposure time was 4 days. Exposure time for cells labeled with 125I-serum was reduced from over 90 days to 14 days. The shortened exposure time for banded chromosomes permitted successful prestaining with Giemsa, a sequence that is not possible without scintillator.     

Dissociation of the protective immune response in the mouse to Strongyloides ratti

The generation of protective immunity by various stages in the life-cycle of Strongyloides ratti and the phases against which resistance is directed has been examined in murine strongyloidiasis. Mice were exposed to natural, complete infections, were treated with thiabendazole (which largely resembles the natural infection), were treated with cambendazole (which restricts infection to the larval stage), or infected directly by oral transfer of adult worms. Mice that were infected with infective larvae alone did not become resistant to infective larvae or the complete infection but were resistant to adult worms implanted directly into the gut. Mice exposed to adult worms alone were resistant to natural infections and adults worms implanted directly but were not resistant to infective larvae. On the other hand, mice that had received prior natural infections showed evidence of resistance to infective larvae, adult worms, and natural, complete infections. It is concluded that there is immunological cross-reactivity between infective larvae and adult worms but that under certain circumstances the infective larvae are able to evade the host's protective immune response.     

Studies on feeding, growth and production of a recruited inshore population of Pleuronectes platessa (L.) at East Anglesey, North Wales

Trawl surveys in an area of 237 km² to the east of Anglesey (Irish Sea) indicated a population of recruited plaice ( c . 480000 fish) between 2 and 15 years old. Seasonal growth began in early April and annual growth in the dominant cohorts was analysed for males and females separately. Net annual production was estimated to be 0.17 g m^-2 from a standing crop of 0.3 g m^-2; c . 50% of the production is removed by fishing. The annual consumption (2.5 g m^-2) of Abra and Pectinaria was converted with 6.8% efficiency by weight (8.0% in energy units).     

A cytophotometric analysis of nuclear DNA contents of cultured human diploid cells in log and in plateau phases of growth

Feulgen-DNA content profiles of cultured human diploid cell strain WI-38 in log and in plateau growth phases were determined by scanning microdensitometry. The results indicate that plateau phase in this cell strain is predominately due to cells becoming blocked in G1.