Short‐term hindlimb unloading induces translocation of nNOS from the sarcolemma to sarcoplasm in skeletal muscle

Abstract

Long duration spaceflight missions cause skeletal muscle atrophy in astronauts. We hypothesize that neuronal Nitric Oxide Synthase (nNOS) and dystrophin translocate from the sarcolemma to the sarcoplasm following 48‐hrs of simulated microgravity as compared to ground controls. Eight Fisher‐344 rats underwent 48‐hour simulated microgravity using the well established hindlimb unloading model, and eight rats were used as ground controls. Hindlimb muscles were carefully dissected, snapped frozen, and stored for analysis. Cryostat sections of soleus muscle (10 micrometer thick), were prepared for immunohistochemical analysis of nNOS and dystrophin localization. Hindlimb unloading induced translocalization of nNOS from the sarcolemma to the sarcoplasm. However, dystrophin was localized at the sarcolemma in the hindlimb unloaded group. Both nNOS and dystrophin were localized to the sarcolemma in the ground control group. These data are the first to demonstrate that nNOS delocalizes from the sarcolema during short‐term hindlimb unloading (48‐hrs). Future studies should investigate the localization of other dystroglycan proteins such as B1‐syntrophin and alpha‐dystrobrevin. Supported by the Texas A&M University Training Grant in Space Life Sciences with funding from NSBRI (NASA NCC 9‐58).