The off rate of Ca(2+) from troponin C is regulated by force-generating cross bridges in skeletal muscle.
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.
Wang
Ying
Y
Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida 33101, USA.
Kerrick
W Glenn L
WG
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006652:Histological Techniques; D066298:In Vitro Techniques; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000502:physiology*; D009218:Myosins / Q000378:metabolism; D013314:Stress, Mechanical; D019209:Troponin C / Q000378:metabolism*; D014732:Vibration
D019209:Troponin C; D009218:Myosins; D002118:Calcium