Inhibition of Ca 2+-pump ATPase and the Na +/K +-pump ATPase by iron-generated free radicals : Protection by 6,7-dimethyl-2,4-di-1-pyrrolidinyl-7 h-pyrrolo[2,3- d]pyrimidine sulfate (U-89843D), a potent, novel, antioxidant/free radical scavenger

Abstract

Preincubation of red blood cell (RBC) membranes with a model system known to generate reactive oxygen species (ROS) and free radicals (200 μM ferrous sulfate and 200 μM EDTA, Fe 2+/EDTA) resulted in inhibition of the Na + K + - pump ATPase, the basal Ca 2+-pump ATPase, and the calmodulin-activated Ca 2+-pump ATPase. Inhibition of the ion pump ATPases was also associated with membrane protein crosslinking and lipid peroxidation, the latter as monitored by the formation of thiobarbituric acid reactive substances (TBARS). Inhibition of the ion transport ATPases, protein cross-linking and formation of TBARS were prevented by U-89843D in a concentration-dependent manner, with half-maximal protection seen at 0.3 μM. U-89843D was more potent than the classical antioxidant butylated hydroxytoluene. Neither U-89843D nor the solvent DMSO had any effect on the assay of TBARS. U-89843D exerted only minimal inhibitory activity on ATPase activities. Thus, U-89843D was potent in vitro in preventing a variety of membrane-damaging reactions mediated by ROS. It is suggested that protection of membranes from ROS-mediated damage is of potential usefulness in the prevention and treatment of certain disease processes.