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© The Rockefeller University Press, 0021-9525/1999//1483 $5.00
The Journal of Cell Biology, Volume 145, Number 7, , 1999 1483-1495

Regular Articles

Thin Filament Protein Dynamics in Fully Differentiated Adult Cardiac Myocytes: Toward A Model of Sarcomere Maintenance



Daniel E. Michele, Faris P. Albayya, and Joseph M. Metzger

Department of Physiology, University of Michigan, Ann Arbor, Michigan 48109-0622

Sarcomere maintenance, the continual process of replacement of contractile proteins of the myofilament lattice with newly synthesized proteins, in fully differentiated contractile cells is not well understood. Adenoviral-mediated gene transfer of epitope-tagged tropomyosin (Tm) and troponin I (TnI) into adult cardiac myocytes in vitro along with confocal microscopy was used to examine the incorporation of these newly synthesized proteins into myofilaments of a fully differentiated contractile cell. The expression of epitope-tagged TnI resulted in greater replacement of the endogenous TnI than the replacement of the endogenous Tm with the expressed epitope-tagged Tm suggesting that the rates of myofilament replacement are limited by the turnover of the myofilament bound protein. Interestingly, while TnI was first detected in cardiac sarcomeres along the entire length of the thin filament, the epitope-tagged Tm preferentially replaced Tm at the pointed end of the thin filament. These results support a model for sarcomeric maintenance in fully differentiated cardiac myocytes where (a) as myofilament proteins turnover within the cell they are rapidly exchanged with newly synthesized proteins, and (b) the nature of replacement of myofilament proteins (ordered or stochastic) is protein specific, primarily affected by the structural properties of the myofilament proteins, and may have important functional consequences.

Key Words: muscle proteins • tropomyosin • troponin • cardiomyocyte • muscle structure

Abbreviations used in this paper: Ab, antibody; KHB, Krebs-Henseleit buffer; MOI, multiplicity of infection; Tm, tropomyosin; TnC, troponin C; TnI, troponin I; TnT, troponin T.

This research was funded by grants from the National Institutes of Health (NIH) and the American Heart Association to J.M. Metzger and NIH Training Grants to D.E. Michele. J.M. Metzger is an Established Investigator for the American Heart Association.


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