Phosphatase inhibitors and premature chromosome condensation in human peripheral lymphocytes at different cell-cycle phases.

The cytogenetical reaction of human peripheral lymphocytes to okadaic acid and calyculin A was examined. Calyculin A could induce PCC about 20 times more effectively than okadaic acid. Their mechanisms of PCC induction were judged similar by their dose-dependent manner and chromosome morphology. Contrary to earlier studies suggesting that chemicals could not induce PCC in G1 cells where little cyclin B is present, the present study showed that calyculin A could induce PCC in lymphocytes not only at S and G2/M but also at the second G1 phase after PHA stimulation in vitro. PCC was induced slightly in lymphocytes both at G0 and the first in vitro G1 phase even when the calyculin A concentration increased one hundred fold. It was found that calcium ionophore A23187 increased frequencies of G0-PCC induced by calyculin A, although a further refinement is necessary to obtain a suitable morphology of G0-PCC for cytogenetic studies.