Extracellular calcium and magnesium, intracellular cyclic AMP, and cell division in Tetrahymen a pyriformis

1. 1. T. pyriformis required ≥ 0.2 mM extracellular magnesium but not exogenous calcium for population growth and DNA synthesis. 2. 2. The intracellular cyclic AMP levels of T. pyriformis were inversely related to cell division rates. 3. 3. When cells were incubated in medium with no added magnesium, minimal cell division occurred, and the intracellular cyclic AMP concentrations were 5-fold greater (100 pmol/mg protein) than in cells in medium with 2 mM magnesium (20 pmol/mg protein). 4. 4. When 2 mM magnesium was added to the cells incubated initially in medium containing < 0.2 mM magnesium, the rate of cell division increased and intracellular cyclic AMP levels declined.