| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 Department of Bioengineering, University of Washington, Seattle, WA 98195, USA
We studied the relative contributions of Ca2+ binding to troponin C (TnC) and myosin binding to actin in activating thin filaments of rabbit psoas fibres. The ability of Ca2+ to activate thin filaments was reduced by replacing native TnC with cardiac TnC (cTnC) or a site I-inactive skeletal TnC mutant (xsTnC). Acto-myosin (crossbridge) interaction was either inhibited using N-benzyl-p-toluene sulphonamide (BTS) or enhanced by lowering [ATP] from 5.0 to 0.5 mM. Reconstitution with cTnC reduced maximal force (Fmax) by 
1/3 and the Ca2+ sensitivity of force (pCa50) by 0.17 unit (P < 0.001), while reconstitution with xsTnC reduced Fmax by 2/3 and pCa50 by 0.19 unit (P < 0.001). In both cases the apparent cooperativity of activation (nH) was greatly decreased. In control fibres 3 µM BTS inhibited force to 57% of Fmax while in fibres reconstituted with cTnC or xsTnC, reconstituted maximal force (rFmax) was inhibited to 8.8% and 14.3%, respectively. Under control conditions 3 µM BTS significantly decreased the pCa50, but this effect was considerably reduced in cTnC reconstituted fibres, and eliminated in xsTnC reconstituted fibres. In contrast, when crossbridge cycle kinetics were slowed by lowering [ATP] from 5 to 0.5 mM in xsTnC reconstituted fibres, pCa50 and nH were increased towards control values. Combined, our results demonstrate that when the ability of Ca2+ binding to activate thin filaments is compromised, the relative contribution of strong crossbridges to maintain thin filament activation is increased. Furthermore, the data suggest that at low levels of Ca2+, the level of thin filament activation is determined primarily by the direct effects of Ca2+ on tropomyosin mobility, while at higher levels of Ca2+ the final level of thin filament activation is primarily determined by strong cycling crossbridges.
(Received 21 October 2004;
accepted after revision 6 December 2004;
first published online 9 December 2004)
Corresponding author M. Regnier: Department of Bioengineering, Box 357962, Seattle, WA 98195-7962, USA. Email: mregnier{at}u.washington.edu
This article has been cited by other articles:
|
|
 |
|
  K. L. Kreutziger, N. Piroddi, B. Scellini, C. Tesi, C. Poggesi, and M. Regnier Thin filament Ca2+ binding properties and regulatory unit interactions alter kinetics of tension development and relaxation in rabbit skeletal muscle J. Physiol., August 1, 2008; 586(15): 3683 - 3700. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. C. Lim, H. Yang, M. Yang, C.-K. Wang, J. Shi, E. A. Berg, D. R. Pimentel, J. K. Gwathmey, R. J. Hajjar, M. Helmes, et al. A Novel Mutant Cardiac Troponin C Disrupts Molecular Motions Critical for Calcium Binding Affinity and Cardiomyocyte Contractility Biophys. J., May 1, 2008; 94(9): 3577 - 3589. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. L. Kreutziger, T. E. Gillis, J. P. Davis, S. B. Tikunova, and M. Regnier Influence of enhanced troponin C Ca2+-binding affinity on cooperative thin filament activation in rabbit skeletal muscle J. Physiol., August 15, 2007; 583(1): 337 - 350. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. E. Gillis, D. A. Martyn, A. J. Rivera, and M. Regnier Investigation of thin filament near-neighbour regulatory unit interactions during force development in skinned cardiac and skeleta muscle J. Physiol., April 15, 2007; 580(2): 561 - 576. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Moreno-Gonzalez, T. E. Gillis, A. J. Rivera, P. B. Chase, D. A. Martyn, and M. Regnier Thin-filament regulation of force redevelopment kinetics in rabbit skeletal muscle fibres J. Physiol., March 1, 2007; 579(2): 313 - 326. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. E. Cantino and A. Quintanilla Cooperative Effects of Rigor and Cycling Cross-Bridges on Calcium Binding to Troponin C Biophys. J., January 15, 2007; 92(2): 525 - 534. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
