[Differences in the protein kinase C activity in CHO-K1 cells and in clone cells of this line resistant to ethidium...

Protein kinase C (PK C) activity in cells of two ethidium bromide (EB) resistant clones with different proliferating rates, derived from CHO-K1 cell line, was assayed. After selection in the presence of 1 mkg/ml EB cells of isolated clones acquired cross-resistance also to some unrelated drugs of different structure. It is shown that resistant cells after the first step of selection elevated PK C activity level in membrane fractions. Subsequent increase in resistance (from 1 to 10 mkg/ml EB) led to a further elevated enzyme activity both in cytosolic and membrane fractions in cells of both variants. The effect of EB presence in cultural media on the enzyme activity was tested. EB at a subtoxic concentration was shown to cause an increased PK C activity both in cytosolic and membrane fractions from resistant cells sublines.