Nitric oxide production and mitochondrial dysfunction during rat thymocyteapoptosis

Production of nitric oxide (NO) by mitochondrial membranes as methemoglobin formation sensitive to N-G-methyl-L-arginine inhibition and mitochondrial O-2 consumption in metabolic states 3 and 4 and the respiratory control (st ate 3/state 4) were measured at early stages of rat thymocyte apoptosis. Pr ogrammed cell death was induced by addition of methylprednisolone and etopo side to thymocyte suspensions. Increased NO production by mitochondrial mem branes was observed after 30 min of methylprednisolone and etoposide additi on and was accompanied by mitochondrial respiratory impairment as an early phenomenon in apoptotic thymocytes. The respiratory control in isolated mit ochondria from untreated thymocytes was 4.2 +/- 0.2 and decreased to 3.1 +/ - 0.2 and 1.9 +/- 0.3 after 1 h of methylprednisolone and etoposide treatme nt, respectively. The low mitochondrial respiratory control was accompanied by a marked decrease in GSH and cytochrome c content. Moreover, an inhibit ory effect in the amount of apoptosis due to thymocyte pretreatment with N- G-methyl-L-arginine and N-omega-nitro-(L)-arginine (L-NNA), indicate that n itric oxide production is closely involved in the signaling of rat thymocyt e apoptosis. (C) 2000 Academic Press.