HUMAN CARDIAC AND SKELETAL-MUSCLE SPECTRINS - DIFFERENTIAL EXPRESSIONAND LOCALIZATION

We describe multiple human cardiac and skeletal muscle spectrin isofor ms. Cardiac muscle expresses five erythroid alpha,beta-spectrin-reacti ve isoforms with estimated M(R)'s of 280, 274, 270, 255, and 246 kD, r espectively. At least one nonerythroid alpha-spectrin of M(R) 284 kD i s expressed in heart. While skeletal muscle shares the 280, 270, and 2 46 kD erythroid spectrins, it expresses an immunologically distinct 28 4 kD nonerythroid alpha-spectrin isoform. The 255 kD erythroid beta-sp ectrin isoform is specific for cardiac tissue. By immunocytochemistry, both erythroid-beta- and nonerythroid alpha-spectrins are localized t o costameres, the plasma membrane, and the neuromuscular junctional re gion.