Calcium influx, intracellular cyclic AMP levels, and DNA synthesis in Tetrahymena pyriformis

Abstract

Abstract o 1. Exogenous agents which reportedly alter either calcium influx or intracellular cyclic AMP levels were added to Tetrahymena pyriformis cultured in defined medium, and subsequently, 45Ca influx, intracellular cyclic AMP levels, and [3H]-thymidine incorporation were measured. 2. The phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), IBMX and epinephrine, IBMX and cyclic AMP, and verapamil all decreased both the calcium influx and the rate of DNA synthesis; none of these agents, however, significantly changed intracellular cyclic AMP levels. 3. Conversely, cholera toxin increased calcium influx and the rate of DNA synthesis but surprisingly did not change intracellular cyclic AMP levels after a 1–30-min incubation. 4. Thus, a change in the rate 45Ca influx was always paralleled by a change in the relative rate of DNA synthesis, while a direct correlation between intracellular cyclic AMP levels and the rate of DNA synthesis was not observed.