In the first experiments (Table 1, expt 1) human diploid cells were routinely subcultured in ISO ml
bow bottles in Eagle's BME medium (Gibco-Biocult Ltd, U.K.) containing 10% foetal calf serum
(FCS), 10% tryptose-phosphate broth. This and all other media used contained 100units of
penicillin and 100 /ig streptomycin per ml. The cells were incubated at 37 °C, with their bottle tops
screwed on tightly. For the remaining experiments in Table 1, the cells were subcultured in 25 cm2
flasks (Nunc Ltd, U.K.) and incubated, with loose bottle tops, in a humidified atmosphere of 5 %
CO2. A richer medium was used in later experiments for routine cell growth (Table 1, expts 6-10).
This was F-15 Eagle's MEM (Gibco-Biocult) supplemented with 10% FCS, 2mM-glutamine. Cells
were subcultured when the culture had attained confluence.They were first washed in phosphate-buffered saline (Dulbecco-PBS 'A') before trypsinizing with 0-5 ml of trypsin-versene
(0'125% trypsin, 0-01 % EDTA). The cell suspension was diluted by the addition of 9-5ml
medium before subculture at 1:4 or 1:8 split ratios for younger cultures, or 1:2 split for slower
growing cultures. The growth medium of non-confluent cultures was changed every 3—4 days. The
cumulative number of population doublings (p.d.) was calculated by counting the number of cells
harvested from each confluent bottle with a Coulter Counter (model ZB1, Coulter Electronics Ltd,
Harpenden, U.K.). (To retain equivalence of p.d. with passages, we score a 1:4 split as 2 passages
and a 1: 8 split as 3 passages.) All cells were routinely screened for mycoplasmal contamination by
the method of Chen (1977). They were all found to be negative. Stocks of cells were maintained by
storing them in growth medium containing 10% glycerol in liquid nitrogen.
In the first experiments (Table 1, expt 1) human diploid cells were routinely subcultured in ISO mlbow bottles in Eagle's BME medium (Gibco-Biocult Ltd, U.K.) containing 10% foetal calf serum(FCS), 10% tryptose-phosphate broth. This and all other media used contained 100units ofpenicillin and 100 /ig streptomycin per ml. The cells were incubated at 37 °C, with their bottle topsscrewed on tightly. For the remaining experiments in Table 1, the cells were subcultured in 25 cm2flasks (Nunc Ltd, U.K.) and incubated, with loose bottle tops, in a humidified atmosphere of 5 %CO2. A richer medium was used in later experiments for routine cell growth (Table 1, expts 6-10).This was F-15 Eagle's MEM (Gibco-Biocult) supplemented with 10% FCS, 2mM-glutamine. Cellswere subcultured when the culture had attained confluence.They were first washed in phosphate-buffered saline (Dulbecco-PBS 'A') before trypsinizing with 0-5 ml of trypsin-versene(0'125% trypsin, 0-01 % EDTA). The cell suspension was diluted by the addition of 9-5mlmedium before subculture at 1:4 or 1:8 split ratios for younger cultures, or 1:2 split for slowergrowing cultures. The growth medium of non-confluent cultures was changed every 3—4 days. Thecumulative number of population doublings (p.d.) was calculated by counting the number of cellsharvested from each confluent bottle with a Coulter Counter (model ZB1, Coulter Electronics Ltd,Harpenden, U.K.). (To retain equivalence of p.d. with passages, we score a 1:4 split as 2 passagesand a 1: 8 split as 3 passages.) All cells were routinely screened for mycoplasmal contamination bythe method of Chen (1977). They were all found to be negative. Stocks of cells were maintained bystoring them in growth medium containing 10% glycerol in liquid nitrogen.
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