Subcellular distribution of dystrophin in isolated adult and neonatal cardiac myocytes.

The subcellular localization of dystrophin was examined in adult rabbit and rat cardiac myocytes with immunofluorescence and at higher resolution with immunogold. The aim was to resolve the conflicting reports on the presence of dystrophin in the transverse tubules (T tubules) of cardiac muscle and to determine its distribution in neonatal myocytes before and during the development of the T tubules. Dystrophin was localized to the peripheral sarcolemma and the T-tubular membrane and was absent from the intercalated disk membranes. In addition, dystrophin localization was followed with immunofluorescence in developing rabbit myocytes at 4 days, 1 wk, and 1 mo after birth. At 4 days of age, T tubules are absent and dystrophin was localized only in the peripheral sarcolemma. Dystrophin was present in the developing T tubules at 1 wk and 1 mo. These results imply that dystrophin is expressed in the T tubules as soon as they develop and confirm the different distribution of dystrophin in the T tubules of cardiac and skeletal muscle.