Standard microelectrode technique was used to study the effect of external free radical generating system (EFR) on action potential of papillary muscle cells of 48 Wistar male rats. EFR were produced from activated oxygen systems: including hydrogen peroxide (H_2O_2), hydroxyl (OH~-) and superoxider (O_2~-). The experiment was divided into six groups: a). control, b). OH~-, c). O_2~-, d). H_2O_2, e). OH~-+catalase(CAT, 150U/ml, f). H_2O_2+CAT and the data were analysed on-line by a computer (Apple Ⅱ Doctor-851). The results showed: (1). a highly significant reduction in action potential amplitude in group OH~- (from 110.5?11.8mV to 98.0?10.4mV), H_2O_2 (from 112.3?13.2mV to 99.0?13.6mV) and O_2~+ (from 117.2?14.5mV to 103.8?13.2mV). (2). a significant decrease in maxium rate of depolariztion (Vmax) respectively (P

Aim To investigate the effects of chloride on the injury of the ventricular myocytes from anoxia-reoxygenation. Methods Under the conditions of anoxia-reoxygenation injury, primary cultured rat ventricular myocytes were treated with 4-acetanide- 4′-isothiocya- natostilbene -2,2′-disulfonic acid (SITS),4,4′,-dii sothiocya-nostilbene-2,2′-disulfonicacid (DIDS) or replaced Cl~- with equimolar gluconate, respectively. Then the cell viability and the contents of Lactate dehydrogenase (LDH), malondialdehyde (MDA), superoxide dismutase (SOD)and glutathione peroxidase (GSH-Px) in the media were measured. Results The release of LDH and MDA was significantly increased in the anoxia-reoxygenation group, while the cell viability and the activity of SOD, GSH-Px decreased significantly compared with those in the control group. In both Cl~--free+ A-R group and SITS+A-R group, LDH and MDA release was noticeably lower than those of the A-R group, while the cell viability and the activity of SOD, GSH-Px significantly increased compared with those in the anoxia-reoxygenation group. But the cell viability and the contents of LDH, MDA, SOD and GSH-Px in the DIDS+A-R group had no significant change compared with those in the anoxia-reoxygenation group.Conclusion Cl~- plays an important role in anoxia reoxygenation injury. SITS provides effective protection to the cardiac myocyte subjected to anoxia reoxygenation injury, while DIDS cannot provide such protection.