Co-localization of nitric oxide synthase I (NOS I) and NMDA receptor subunit 1 (NMDAR-1) at the neuromuscular junction in rat and mouse skeletal muscle.
Nitric oxide synthase I (NOS I) has been localized to the skeletal muscle sarcolemma in a variety of vertebrate species including man. It is particularly enriched at neuromuscular junctions. Recently, the N-methyl-D-aspartate (NMDA) receptor subunit 1 (NMDAR-1) has been detected in the postjunctional sarcolemma of rat diaphragm, providing a clue as to the possible source of Ca2+ ions that are necessary for NOS I activation. To address this possibility, we studied the distribution of NMDAR-1 and NOS I in mouse and rat skeletal muscles by immunohistochemistry and enzyme histochemistry. NMDAR-1 and NOS I were closely associated at neuromuscular junctions primarily of type II muscle fibers. NOS I was also present in the extrajunctional sarcolemma of this fiber type. Dystrophin, beta-dystroglycan, alpha-sarcoglycan, and spectrin were found normally expressed in both the junctional and extrajunctional sarcolemma of both fiber types. By contrast, in the muscle sarcolemma of MDX mice, dystrophin and dystrophin-associated proteins were reduced or absent. NOS I immunoreactivity was lost from the extrajunctional sarcolemma and barely detectable in the junctional sarcolemma. NOS I activity was clearly demonstrable in the junctional sarcolemma by NADPH diaphorase histochemistry, especially when the two-step method was used. NMDAR-1 was not altered. These data suggest that different mechanisms act to attach NOS I to the junctional versus extrajunctional sarcolemma. It may further be postulated that NMDA receptors are involved not only in the regulation but also sarcolemmal targeting of NOS I at neuromuscular junctions of type II fibers. The evidence that glutamate may function as a messenger molecule at vertebrate neuromuscular junction is discussed.
Grozdanovic
Z
Z
Institute of Anatomy, Department of Molecular Anatomy and Cell Biology, University Clinic Benjamin Franklin, Free University of Berlin, D-14195 Berlin, Germany.
Gossrau
R
R
D000818:Animals; D006224:Cricetinae; D003598:Cytoskeletal Proteins / Q000032:analysis; D049030:Dystroglycans; D016189:Dystrophin / Q000172:deficiency; D005260:Female; D005849:Gerbillinae; D006168:Guinea Pigs; D008297:Male; D008562:Membrane Glycoproteins / Q000032:analysis; D008565:Membrane Proteins / Q000032:analysis; D008647:Mesocricetus; D051379:Mice; D018101:Mice, Inbred mdx; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000201:enzymology / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000166:cytology / Q000294:innervation* / Q000648:ultrastructure; D009469:Neuromuscular Junction / Q000737:chemistry* / Q000201:enzymology*; D019001:Nitric Oxide Synthase / Q000032:analysis*; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000032:analysis*; D049031:Sarcoglycans; D012508:Sarcolemma / Q000737:chemistry / Q000201:enzymology; D013045:Species Specificity; D013049:Spectrin / Q000032:analysis; D049411:Utrophin
D003598:Cytoskeletal Proteins; D016189:Dystrophin; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D016194:Receptors, N-Methyl-D-Aspartate; D049031:Sarcoglycans; C483600:Utrn protein, mouse; D049411:Utrophin; D013049:Spectrin; D049030:Dystroglycans; D019001:Nitric Oxide Synthase