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* Centre for Microscopy and Microanalysis, Department of Physiology and Pharmacology, and Centre for Molecular and Cellular
Biology, University of Queensland, Queensland 4072, Brisbane, Australia; and Caveolae, flask-shaped invaginations of the
plasma membrane, are particularly abundant in muscle
cells. We have recently cloned a muscle-specific caveolin, termed caveolin-3, which is expressed in differentiated muscle cells. Specific antibodies to caveolin-3 were
generated and used to characterize the distribution of
caveolin-3 in adult and differentiating muscle. In fully
differentiated skeletal muscle, caveolin-3 was shown to
be associated exclusively with sarcolemmal caveolae.
Localization of caveolin-3 during differentiation of primary cultured muscle cells and development of mouse
skeletal muscle in vivo suggested that caveolin-3 is transiently associated with an internal membrane system.
These elements were identified as developing transverse-(T)-tubules by double-labeling with antibodies to
the
European Molecular Biology Laboratory,
D69012 Heidelberg, Germany
1 subunit of the dihydropyridine receptor in
C2C12 cells. Ultrastructural analysis of the caveolin-3-
labeled elements showed an association of caveolin-3
with elaborate networks of interconnected caveolae,
which penetrated the depths of the muscle fibers. These elements, which formed regular reticular structures,
were shown to be surface-connected by labeling with
cholera toxin conjugates. The results suggest that caveolin-3 transiently associates with T-tubules during development and may be involved in the early development
of the T-tubule system in muscle.
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