The presence of two skeletal muscle α-actinins correlates with troponin-tropomyosin expression and Z-line width

Abstract

Two species of α-actinin from rabbit fast skeletal muscles were identified with a monospecific antisera. Designated α-actininlf and α-actinin2f, their distribution in muscles does not correlate with histochemically defined fast fiber type. Rather, the presence of each correlates with Z-line width and with the expression of different thin filament Ca2+-regulatory complexes, α-Actininlf is expressed with troponin Tlf-αβ tropomyosin, and α-actinin2f with troponin T2f-α2 tropomyosin. CNBr peptide maps show that the fast α-actinin species differ in primary structure. In contrast, the slow α-actinin is indistinguishable from a-actininlf. Further evidence for the similarity of α-actinin1f and slow a-actinin comes from electron microscopic studies which show that fibers that express these species exhibit thick Z-lines. So, unlike other contractile proteins, the multiple forms of α-actinin do not reflect the distinction between fast- and slow-twitch muscles. © 1985, Rockefeller University Press., All rights reserved.