Human cardiac and skeletal muscle spectrins: Differential expression and localization

We describe multiple human cardiac and skeletal muscle spectrin isoforms. Cardiac muscle expresses five erythroid α,β spectrin‐reactive isoforms with estimated M R 's of 280, 274, 270, 255, and 246 kD, respectively At least one nonerythroid α‐spectrin of M R 284 kD is expressed in heart. While skeletal muscle shares the 280, 270, and 246 kD erythroid spectrins, it expresses an immunologically distinct 284 kD nonerythroid α‐spectrin isoform. The 255 kD erythroid β‐spectrin isoform is specific for cardiac tissue. By immunocytochemistry, both erythroid β‐ and nonerythroid α‐spectrins are localized to costameres, the plasma membrane, and the neuromuscular junctional region.