Details

Autor(en) / Beteiligte

• Brotto, Marco A
• Biesiadecki, Brandon J
• Brotto, Leticia S
• Nosek, Thomas M
• Jin, Jian-Ping

Titel

Coupled expression of troponin T and troponin I isoforms in single skeletal muscle fibers correlates with contractility

Ist Teil von

• American Journal of Physiology: Cell Physiology, 2006-02, Vol.290 (2), p.C567-C576

Ort / Verlag

United States

Erscheinungsjahr

2006

Quelle

MEDLINE

Beschreibungen/Notizen

• Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio Submitted 22 August 2005 ; accepted in final form 19 September 2005 Striated muscle contraction is powered by actin-activated myosin ATPase. This process is regulated by Ca 2+ via the troponin complex. Slow- and fast-twitch fibers of vertebrate skeletal muscle express type I and type II myosin, respectively, and these myosin isoenzymes confer different ATPase activities, contractile velocities, and force. Skeletal muscle troponin has also diverged into fast and slow isoforms, but their functional significance is not fully understood. To investigate the expression of troponin isoforms in mammalian skeletal muscle and their functional relationship to that of the myosin isoforms, we concomitantly studied myosin, troponin T (TnT), and troponin I (TnI) isoform contents and isometric contractile properties in single fibers of rat skeletal muscle. We characterized a large number of Triton X-100-skinned single fibers from soleus, diaphragm, gastrocnemius, and extensor digitorum longus muscles and selected fibers with combinations of a single myosin isoform and a single class (slow or fast) of the TnT and TnI isoforms to investigate their role in determining contractility. Types IIa, IIx, and IIb myosin fibers produced higher isometric force than that of type I fibers. Despite the polyploidy of adult skeletal muscle fibers, the expression of fast or slow isoforms of TnT and TnI is tightly coupled. Fibers containing slow troponin had higher Ca 2+ sensitivity than that of the fast troponin fibers, whereas fibers containing fast troponin showed a higher cooperativity of Ca 2+ activation than that of the slow troponin fibers. These results demonstrate distinct but coordinated regulation of troponin and myosin isoform expression in skeletal muscle and their contribution to the contractile properties of muscle. skinned single fiber; myosin; diaphragm; soleus; gastrocnemius; extensor digitorum longus Address for reprint requests and other correspondence: J.-P. Jin, Section of Molecular Cardiology, Evanston Northwestern Healthcare and Feinberg School of Medicine, Northwestern Univ., 2650 Ridge Ave., Evanston, IL 60201 (e-mail: jpjin{at}northwestern.edu )