Nitric oxide synthase I (NOS-I) is deficient in the sarcolemma of striated muscle fibers in patients with Duchenne muscular dystrophy, suggesting an association with dystrophin.

Previously, we have demonstrated the expression of the brain-type nitric oxide synthase (NOS-I) in the sarcolemmal region of somatic and visceral striated muscle fibers in a variety of mammalian species through the use of enzyme histochemical and immunochemical techniques. Here we report that NOS-I protein and its NADPH diaphorase (NADPHd) activity are co-localized in the sarcolemma of human skeletal muscles. NOS-I immunolabeling and NADPHd activity showed no significant variation between type I and II fibers. In muscle biopsy specimens from patients with Duchenne muscular dystrophy (DMD), both NOS-I protein and activity were absent or markedly reduced. We, therefore, propose that NOS-I is complexed with dystrophin and/or dystrophin-associated proteins, adding a novel member to the sarcolemmal dystrophin-glycoprotein complex (DGC). The nature of the NOS-I-DGC link, and its role in skeletal muscle physiology and pathophysiology remain to be elucidated.