Ecto-ATPase activity in rat and mouse thymocytes and cytotoxic effects of various chemical substances in vitro

Ecto-ATPase was present in thymocytes of mice and rats with higher activity in rat thymocytes. In rat but not in mouse thymocytes the ecto-ATPase was inhibited in vitro by HgCl2, tricyclohexyltin chloride, di-n-butyltin dichloride, DDT, gamma HCH and desipramine. The EC50 values ranged from 8 X 10(-7) mol/l for HgCl2 to 4 X 10(-4) mol/l for desipramine. Ecto-ATPase activity in thymocytes was not a valuable indicator of the cytotoxic effects of chemicals in vitro. Inhibition of the enzyme was not accompanied by changes of the electrophoretic mobility of thymocytes. A decrease of the spontaneous mitotic activity of thymocytes in vitro is a very sensitive parameter of cytotoxic and cytostatic drug effects.