Abstract
Background. Mutations in the dystrophin gene produce clinical manifestations of disease in heart, brain, and skeletal muscle in patients with Duchenne and Beckers muscular dystrophy (DMD/BMD). Conduction disturbances and heart block contribute to cardiac decompensation in these patients, which suggests an important role for dystrophin in the cardiac conduction system. We therefore examined the messenger RNA (mRNA) expression and protein localization of dystrophin in normal human cardiac Purkinje fibers. Methods and Results. Polymerase chain reaction amplification of isolated Purkinje fiber complementary DNA identified several alternatively spliced mRNA transcripts encoding for carboxy-terminal isoforms of the dystrophin protein. The predominant mRNA transcript detected was a splice form previously detected in the brain. Antipeptide antibodies specific for a carboxy-terminal dystrophin sequence were used for Western blot analysis and immunocytochemical localization. These antisera detect ≈400,000-d immunoreactive band or bands on Western blot in normal heart and Purkinje fibers but not in DMD heart. Immunocytochemical staining showed that dystrophin was localized to the membrane surface of the Purkinje fiber. Conclusions. These results suggest that dystrophin may be an important molecule for membrane function in the Purkinje conduction system of the heart and support the hypothesis that defective dystrophin expression contributes to the cardiac conduction disturbances seen in DMD/BMD.