EFFECT OF HYPOXIA ON PROXIMAL TUBULES ISOLATED FROM NITRIC-OXIDE SYNTHASE KNOCKOUT MICE

Nitric oxide (NO) has been shown to be a mediator of hypoxic injury in rat renal proximal tubules (PT). However, the role of NO in hypoxic i njury to mouse PT has not been examined. The aim of the present study was to determine the effect of knockout of nitric oxide synthase (NOS) isoforms on hypoxic injury in mouse PT. Mouse PTs were isolated by co llagenase digestion and Percoll centrifugation. The nonselective NOS i nhibitor, N-nitro-L-arginine methyl ester (L-NAME, 10 mM), but not its inactive stereoisomer D-NAME, protected against hypoxic injury as ass essed by LDH release. Carboxy-imidazolineoxyl N-oxide (carboxy-PTIO, 1 00 mu M), a stable NO scavenger, also afforded cytoprotection against hypoxic injury. To determine the role of the different NOS isoforms in the hypoxic injury, we examined the effect of hypoxia on PT isolated from knockout mice in which either the inducible NOS (iNOS), endotheli al NOS (eNOS) or neuronal NOS (nNOS) gene was lacking. PT isolated fro m iNOS knockout mice were resistant to hypoxic injury compared to wild -type controls. In contrast, PT isolated from both nNOS and eNOS knock out mice were not protected against hypoxic injury. In conclusion, the present study demonstrates that NO is a mediator of hypoxic PT injury in the mouse and that knockout of the iNOS gene is cytoprotective aga inst this hypoxic PT injury.