Human cardiac and skeletal muscle spectrins: Differential expression and localization

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Abstract
We describe multiple human cardiac and skeletal muscle spectrin isoforms. Cardiac muscle expresses five erythroid α,β spectrin-reactive isoforms with estimated MR's of 280, 274, 270, 255, and 246 kD, respectively At least one nonerythroid α-spectrin of MR 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.