The off rate of Ca2+ from troponin C is regulated by force-generating cross bridges in skeletal muscle

• Published in: Journal of applied physiology (1985) Vol. 92; no. 6; pp. 2409 - 2418
• Main Authors: Wang, Ying, Kerrick, W. Glenn L
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01-06-2002; American Physiological Society
• Subjects: Biological and medical sciences; Calcium; Fundamental and applied biological sciences. Psychology; Muscular system; Phosphates; Striated muscle. Tendons; Vertebrates: osteoarticular system, musculoskeletal system; Calcium; Force; Rodentia; Electrophysiology; Striated muscle; Muscle contraction; Lumbrical muscle; Biomechanics; Vertebrata; Troponin; Mammalia; Mouse; Mechanical stress; Dissociation; Intracellular
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00376.2001

Department of Physiology and Biophysics, University of
Miami School of Medicine, Miami, Florida 33101
The
effects of dissociation of force-generating cross bridges on
intracellular Ca 2+ , pCa-force, and pCa-ATPase relationships
were investigated in mouse skeletal muscle. Mechanical length
perturbations were used to dissociate force-generating cross bridges in
either intact or skinned fibers. In intact muscle, an impulse stretch
or release, a continuous length vibration, a nonoverlap stretch, or an
unloaded shortening during a twitch caused a transient increase in
intracellular Ca 2+ compared with that in isometric controls
and resulted in deactivation of the muscle. In skinned fibers,
sinusoidal length vibrations shifted pCa-force and pCa-actomyosin
ATPase rate relationships to higher Ca 2+ concentrations and
caused actomyosin ATPase rate to decrease at submaximal
Ca 2+ and increase at maximal Ca 2+ activation.
These results suggest that dissociation of force-generating cross
bridges during a twitch causes the off rate of Ca 2+ from
troponin C to increase (a decrease in the Ca 2+ affinity of
troponin C), thus decreasing the Ca 2+ sensitivity and
resulting in the deactivation of the muscle. The results also suggest
that the Fenn effect only exists at maximal but not submaximal
force-activating Ca 2+ concentrations.
force; intracellular calcium ion; actomyosin
adenosinetriphosphatase; mechanical length perturbation; deactivation