Ultrastructural localization of alpha 1-syntrophin and neuronal nitric oxide synthase in normal skeletal myofiber, and their relation to each other and to dystrophin.

We investigated the ultrastructural localization of alpha 1-syntrophin and neuronal nitric oxide synthase (nNOS) in normal human skeletal myofibers and analyzed their relation to each other and to dystrophin using single and double immunogold-labeling electron microscopy. Single immunolabeling showed antibodies to alpha 1-syntrophin and nNOS on the inner surface of the muscle plasma membrane, the sarcoplasmic side of plasma membrane invaginations, and the sarcoplasm near mitochondria of subsarcolemmal areas. The epitopes of alpha 1-syntrophin and nNOS tended to be present in clusters. Double immunolabeling revealed that epitope combinations of alpha 1-syntrophin-dystrophin, alpha 1-syntrophin-nNOS, and nNOS-dystrophin occurred more frequently in doublet form than did other epitope combinations, such as alpha 1-syntrophin-beta- spectrin and nNOS-beta-spectrin. These increased frequencies were noted both at the muscle plasma membrane undercoat and near mitochondria of subsarcolemmal areas. A significantly higher percentage of doublets comprised antibodies against alpha 1-syntrophin and dystrophin (28.5 +/- 1.5%, group mean +/- SE) than those against alpha 1-syntrophin and beta-spectrin (9.2 +/- 0.8%, P < 0.01). Furthermore, nNOS formed doublets significantly more frequently with dystrophin (25.2 +/- 3.3%) and alpha 1-syntrophin (26.0 +/- 4.1%) than with beta-spectrin (13.9 +/- 2.3%; P < 0.05). These data support the association of dystrophin, alpha 1-syntrophin, and nNOS at the inner surface of the muscle plasma membrane and near mitochondria of subsarcolemmal areas of normal human skeletal myofibers.