INDUCIBLE NO SYNTHASE-II AND NEURONAL NO SYNTHASE-I ARE CONSTITUTIVELY EXPRESSED IN DIFFERENT STRUCTURES OF GUINEA-PIG SKELETAL-MUSCLE - IMPLICATIONS FOR CONTRACTILE FUNCTION

The expression of NOS isoforms was studied in guinea pig skeletal musc le at the mRNA and protein level, and the effect of NO on contractile response was examined, Ribonuclease protection analyses demonstrated N OS I and NOS II mRNAs in diaphragm and gastrocnemius muscle, In Wester n blots, NOS I and NOS II immunoreactivities were found in the particu late but not the soluble fraction of skeletal muscle, NOS activity was found almost exclusively in the particulate fraction, About 50% of th is activity was Ca2+ independent, In immunohistochemistry, the anti-NO S I antibody stained distinct membrane regions of muscle fibers, The m ost intense staining was seen in neuromuscular endplates identified by labeling with a-bungarotoxin, The anti-NOS II antibody labeled muscle fibers that contained alkalilabile myosin ATPase (type I fibers), NOS II was located to intracellular structures and was also seen in ''spe cific pathogen-free'' animals. Pretreatment of guinea pigs with bacter ial lipopolysaccharide (LPS) markedly intensified NOS II staining, Sig nificant NOS III immunoreactivity was detected only in vascular endoth elium. In functional experiments, tetanic muscle contractions were ind uced in diaphragm and gastrocnemius muscle by electrical stimulation o f the innervating nerves, Pretreatment of guinea pigs with LPS or addi tion of S-nitroso-N-acetyl-D,L-penicillamine to the organ bath markedl y decreased tetanic contractions, N-G-nitro-L-arginine, on the other h and, increased contractile force and reversed the effect of LPS, Our d ata indicate that NOS II and NOS I are expressed in different structur es of skeletal muscle and are involved in the regulation of contractil e response.