Search for aquaporin molecules at the plasma membrane of normal skeletal myofibers and their alterations in myopathic muscles.

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We investigated what kind of aquaporin molecule is expressed in normal skeletal muscle and the investigation was extended to analyze the alteration of the expression of these aquaporin molecule in the diseased human muscles. With regard to the expression of aquaporin molecule in normal skeletal muscle, each of aquaporin 0〜10 molecule was searched at RNA and protein levels. The investigation of RNA level was carried out by RT PCR and that of protein level was performed by immunoblot and immunocytochemistry As the result, AQP3, AQP4 AQP7 molecules were confirmed to be present at RNA and protein levels in normal human skeletal myofibers. AQP4 molecule was more abundantly expressed in type 2 white fiber (fast twitch fiber) than in type 1 red fiber (slow twitch fiber): whereas AQP3 molecule was more abundantly expressed in type 1 red fiber than in type 2 white fiber. AQP7 molecule was equally expressed in type 1 and type 2 human skeletal myofibers; while in normal mouse skeletal muscle AQP7 … More was more abundantly expressed in type 2 fast twitch fiber than type 1 slow twitch fiber. AQP 1 is reported to be present at the endothelial cell within skeletal muscle tissue, however; we noticed that AQP 1 is present at the myofiber surface of skeletal muscle tissue. Electron microscopy of fracture label replica of normal skeletal muscle showed that gold signal of AQP4 was located in the orthogonal array of myofiber P face and that of AQP3 was located in the particle cluster of myofiber P face. Particle cluster is the irregular aggregate of intramembranous particles and is different from orthogonal array which is the regular particle aggregate more than 4 particles forming rectangular shape. With respect to the altered expression of aquaporin molecule in diseased human skeletal muscles, expression of AQP4 in muscles with Fukuyama type congenital muscular dystrophy was reduced in their myofiber surface at protein levels and the content of AQP4 mRNA was reduced AQP4 expression was also decreased in the scattered myofibers with neurogenic atrophy muscles such as muscles with amyotrophic lateral sclerosis. Less