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It was determined that change in DNA content in macronuclei occurs in the T. pyriformis infuso ria under the influence of an activator (caffeine) and inhibitors of Ca 2+ channels (verapamil), NiCl 2 , and CdCl 2 . Caffeine (10 mM) stimulates DNA synthesis. Verapamil (5 µM), CdCl 2 (125 µM), and NiCl 2 (100 µM) decrease DNA content in macronuclei by 30 min after proliferative stimulation. By 4 h of incuba tion, there is, on average, 10% less DNA in macronuclei of Tetrahymena preprocessed with verapamil than in the control cells. The cells preprocessed with CdCl 2 and NiCl 2 differ from the control cells by lower DNA content almost at all studied periods, but they restore the level of nuclear DNA by 4 h. It is assumed that trans mission of proliferative signals in the T. pyriformis has a Ca 2+ dependent character.

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