[3H]-Thymidine Incorporation.
Cell proliferation was deter-
mined by measuring the incorporation of [3H]-thymidine into DNA
of cells cultured in 24-well plates.
17,18 After induction of quiescence, the
cells were stimulated with high glucose (30 mM) or normal glucose
concentration (5.5 mM) in the presence or absence of EGCG for the
indicated times. Thereafter, [3H]-thymidine (1μCi/mL) was added to
the growth medium of each well 6 h prior to the measurements. At the
end of incubation, the medium was removed and the cells were treated
with 0.25 mL of 0.05% trypsin
0.53 mmol/L EDTA for 5 min and
diluted to 10 mL with a balanced electrolyte solution. The cells were
then treated with 10% trichloroacetic acid to precipitate acid-insoluble
materials from which the DNA was extracted with 0.1 N NaOH. The
DNA was collected on a Whatman GF/B filter and washed twice with
5 mL of ice-cold PBS. The filter was then cut and shaken in 3.5 mL of
scintillation fluid for 24 h before counting in a liquid scintillation counter
(Beckman LS6500). Data are presented as [
3
H]-thymidine uptake per
microgram of protein. The protein refers to the total protein of the cell
sample.