NO synthase II in mouse skeletal muscle is associated with caveolin 3

The inducible-type NO synthase (NOS II; iNOS) is constitutively expressed i n slow-twitch skeletal muscle fibres of guinea-pigs [Gath, Closs, Godtel-Ar mbrust, Schmitt, Nakane, Wessler and Forstermann (1996) FASEB J. 10, 1614-1 620]. Here we studied the expression of NOS II in skeletal muscle of wild-t ype and NOS II-deficient mice and investigated the molecular basis for the membrane association of this NOS in muscle. A basal expression of NOS II mR NA and protein was detected in skeletal muscle from untreated wild-type mic e; expression increased when mice were treated with bacterial lipopolysacch aride (LPS). No NOS II was found in any tissue of untreated or LPS-treated NOS II-deficient mice. Immunoprecipitation experiments were performed with homogenates of gastrocnemius muscle from untreated or LPS-treated wild-type mice. A NOS II-specific antibody precipitated caveolin 3 in all homogenate s investigated, the effect being most pronounced in skeletal muscle from LP S-treated animals. Conversely, an antibody against caveolin 3 co-precipitat ed NOS II in muscle homogenates. Similarly, a weak co-precipitation of NOS II and caveolin 3 was seen in homogenates of untreated murine C2C12 myotube s; coprecipitation was markedly enhanced in cells stimulated with LPS/inter feron gamma. The association of NOS II with caveolin 3 might have implicati ons for the regulation of contraction of, and/or glucose uptake by, slow-tw itch muscle fibres.