The role of tropomyosin in the regulation of myocardial contraction and relaxation.

Studies over the last 30 years have demonstrated the essential nature of the evolutionarily highly conserved tropomyosin (TM) protein. TM-deficient cells neither function properly nor survive, and mutations within this protein impair severely its function within the sarcomere. The ability to manipulate TM isoform expression genetically within functioning cardiomyocytes and the whole heart has proven essential in deciphering the physiological significance of the different TM isoforms. It is now apparent that alpha-TM and actin serve as the requisite backbone of the thin filament, with varying levels of beta- and gamma-TM, together with the troponin complex serving to modulate sarcomere function. Defining the mechanisms whereby specific TM isoform amino acid differences alter thin filament dynamics will enhance greatly the understanding of muscle contraction during both normal and pathological states.