Nitric oxide synthase I (NOS I) is a costameric enzyme in rat skeletal muscle.

Previously, we and others have reported association of nitric oxide (NO)-generating nitric oxide synthase I (NOS I) with dystrophin in the subsarcolemmal cytoskeleton of striated muscle fibers. Since this structure shows a costameric organization the detailed distribution of NOS I and other molecules inside and outside the subsarcolemmal cytoskeleton was investigated. Using catalytic histochemistry and immunohistochemistry on rat skeletal muscle NOS I was colocalized in the costameres together with dystrophin, beta-dystroglycan, alpha-, beta- and gamma-sarcoglycan, beta 1-integrin, vinculin, paxillin and caveolin-3. Additionally, only NOS appeared in uncharacterized subsarcolemmal wave-like structures. These data show 1) a growing family of proteins assembled in the costameres including NOS I as described here for the first time, 2) expanded distribution patterns for NOS I, and 3) therefore, presumably uneven NO concentrations within the skeletal muscle fibers which may have implications for NO function.