Caveolin-3 is associated with the T-tubules of mature skeletal muscle fibers

Caveolae are abundant in skeletal muscle and their coat contains a specific isoform of caveolin, caveolin-3, It has been suggested that during muscle development, caveolin-3 is associated with the T-tubules, but that in adult muscle it is found on the plasma membrane only. We have studied the distri bution of caveolin-3 in single skeletal muscle; fibers from adult rat soleu s by confocal immunofluorescence and by immunogold electron microscopy. We found that caveolin-3 occurs at the highest density on the plasma membrane but is also present in the core of the fibers, at the I-band/A-band interfa ce where it is associated with the T-tubules, In neither domain of the musc le surface does caveolin-3 colocalize with the glucose transporter GLUT4 an d there is no evidence for internalization of the caveolae in muscle. (C) 1 999 Academic Press.