NO DONOR SIN-1 PROTECTS AGAINST REOXYGENATION-INDUCED CARDIOMYOCYTE INJURY BY A DUAL-ACTION

It was investigated whether morpholinosydnonimine (SIN-1), which spont aneously decomposes into NO and 3-morpholinoiminoacetonitrile (SIN-1C) , can be used for protection of cardiomyocytes against reoxygenation-i nduced hypercontracture. Isolated ventricular cardiomyocytes (from adu lt rats) were used as the experimental model. SIN-1 [concentration wit h half-maximal effect (EC(50)) 2.5 x 10(-4) M] and SIN-1C (EC(50) 8.3 x 10(-3) M) inhibited the contractile response of electrically paced c ardiomyocytes. When the cells were submitted to substrate-free anoxia (135 min) and subsequent reoxygenation (30 min), the onset of reoxygen ation provoked their hypercontracture. It was studied whether the temp orary presence of the test agents during the last 15 min of anoxia and the first 15 min of reoxygenation prevented hypercontracture. At 10 m M, SIN-1 prevented hypercontracture in 96% of the cells and SIN-1C in 72% of the cells. The protective effect of SIN-1 was reduced to that o f SIN-1C by simultaneous presence of methylene blue (50 mu M). Methyle ne blue had no influence on the protective action of SIN-IC. SIN-1C (1 0 mM) plus sodium nitroprusside (another NO donor, 250 mu M) provided the same degree of protection as SIN-1 (10 mM). The results show that reoxygenation-induced hypercontracture can be prevented or attenuated by the temporary presence of high concentrations of SIN-1 or SIN-IC. S IN-1 acts through a dual mechanism, protecting through the generation of NO and SIN-1C.