Activity and expression of nitric oxide synthase in pork skeletal muscles.

The objective of this study was to investigate the biochemical changes of nitric oxide synthase (NOS) in pork skeletal muscles during postmortem storage. Longissimus thoracis (LT), psoas major (PM) and semimembranosus (SM) muscles of pork were removed immediately after slaughter and stored under vacuum condition at 4°C for 0, 1 and 3d. Results showed that all three muscles exhibited NOS activity until 1d while SM muscle retained NOS activity after 3d of storage. The content of nNOS in SM muscle was stable across 3d of storage while decreased intensity of nNOS was detected at 1 and 3d of aging in PM and LT muscles due to the degradation of calpain. Immunostaining showed that nNOS was located at not only sarcolemma but also cytoplasm at 0 and 1d of storage. Our data suggest that postmortem muscles possess NOS activity and nNOS expression depends on muscle type.