Slowed Dynamics of Thin Filament Regulatory Units Reduces Ca2+-Sensitivity of Cardiac Biomechanical Function
- 148 Downloads
Actomyosin kinetics in both skinned skeletal muscle fibers at maximum Ca2+-activation and unregulated in vitro motility assays are modulated by solvent microviscosity in a manner consistent with a diffusion limited process. Viscosity might also influence cardiac thin filament Ca2+-regulatory protein dynamics. In vitro motility assays were conducted using thin filaments reconstituted with recombinant human cardiac troponin and tropomyosin; solvent microviscosity was varied by addition of sucrose or glucose. At saturating Ca2+, filament sliding speed (s) was inversely proportional to viscosity. Ca2+-sensitivity (pCa 50) of s decreased markedly with elevated viscosity (η/η 0 ≥ ~1.3). For comparison with unloaded motility assays, steady-state isometric force (F) and kinetics of isometric tension redevelopment (k TR) were measured in single, permeabilized porcine cardiomyocytes when viscosity surrounding the myofilaments was altered. Maximum Ca2+-activated F changed little for sucrose ≤0.3 M (η/η 0 ~ 1.4) or glucose ≤0.875 M (η/η 0 ~ 1.66), but decreased at higher concentrations. Sucrose (0.3 M) or glucose (0.875 M) decreased pCa 50 for F. k TR at saturating Ca2+ decreased steeply and monotonically with increased viscosity but there was little effect on k TR at sub-maximum Ca2+. Modeling indicates that increased solutes affect dynamics of cardiac muscle Ca2+-regulatory proteins to a much greater extent than actomyosin cross-bridge cycling.
KeywordsSkinned myocyte Myosin Actin Troponin Tropomyosin In vitro motility assay Kinetics of isometric tension redevelopment Microviscosity Monosaccharide glucose Disaccharide sucrose
This work was supported by National Institute of Health grants HL63974 (PBC), a Florida State University Center for Materials Research and Technology (MARTECH) Pre-doctoral Fellowship (MAB), and American Heart Association Pre-doctoral Fellowships 0615164B (AKT) and 0815127E (CKPL). We thank Bradley’s Country Store, Tallahassee, FL, for generously supplying porcine hearts.
Conflict of interest
The authors have no conflicts of interest to declare.
- 5.Brunet, N. M., G. Mihajlović, K. Aledealat, F. Wang, P. Xiong, S. von Molnár, and P. B. Chase. Micromechanical thermal assays of Ca2+-regulated thin-filament function and modulation by hypertrophic cardiomyopathy mutants of human cardiac troponin. J. Biomed. Biotechnol. 2012:657523, 2012.CrossRefGoogle Scholar
- 9.Chase, P. B., Y. Chen, K. Kulin, and T. L. Daniel. Viscosity and solute dependence of F-actin translocation by rabbit skeletal heavy meromyosin. Am. J. Physiol. Cell Physiol. 278:C1088–C1098, 2000.Google Scholar
- 12.Édes, I. F., D. Czuriga, G. Csányi, S. Chłopicki, F. A. Recchia, A. Borbély, Z. Galajda, I. Édes, J. van der Velden, G. J. M. Stienen, and Z. Papp. Rate of tension redevelopment is not modulated by sarcomere length in permeabilized human, murine, and porcine cardiomyocytes. Am. J. Physiol. Regul. Integr. Comp. Physiol. 293:R20–R29, 2007.CrossRefGoogle Scholar
- 13.Endo, M., T. Kitazawa, M. Iino, and Y. Kakuta. Effect of “viscosity” of the medium on mechanical properties of skinned skeletal muscle fibers. In: Cross-Bridge Mechanism in Muscle Contraction, edited by H. Sugi, and G. H. Pollack. Tokyo: University of Tokyo Press, 1979, pp. 365–374.Google Scholar
- 18.Gordon, A. M., E. Homsher, and M. Regnier. Regulation of contraction in striated muscle. Physiol. Rev. 80:853–924, 2000.Google Scholar
- 23.Homsher, E., F. Wang, and J. R. Sellers. Factors affecting movement of F-actin filaments propelled by skeletal muscle heavy meromyosin. Am. J. Physiol. 262:C714–C723, 1992.Google Scholar
- 24.Köhler, J., Y. Chen, B. Brenner, A. M. Gordon, T. Kraft, D. A. Martyn, M. Regnier, A. J. Rivera, C.-K. Wang, and P. B. Chase. Familial hypertrophic cardiomyopathy mutations in troponin I (K183Δ, G203S, K206Q) enhance filament sliding. Physiol. Genomics 14:117–128, 2003.Google Scholar
- 27.Lamb, G. D., D. G. Stephenson, and G. J. Stienen. Effects of osmolality and ionic strength on the mechanism of Ca2+ release in skinned skeletal muscle fibres of the toad. J. Physiol. 464:629–648, 1993.Google Scholar
- 28.Landesberg, A., and S. Sideman. Coupling calcium binding to troponin C and cross-bridge cycling in skinned cardiac cells. Am. J. Physiol. 266:H1260–H1271, 1994.Google Scholar
- 50.Schiaffino, S., and C. Reggiani. Molecular diversity of myofibrillar proteins: gene regulation and functional significance. Physiol. Rev. 76:371–423, 1996.Google Scholar
- 51.Schoffstall, B., N. M. Brunet, F. Wang, S. Williams, A. T. Barnes, V. F. Miller, L. A. Compton, L. A. McFadden, D. W. Taylor, R. Dhanarajan, M. Seavy, and P. B. Chase. Ca2+-sensitivity of regulated cardiac thin filament sliding does not depend on myosin isoform. J. Physiol. 577:935–944, 2006.CrossRefGoogle Scholar
- 54.Schoffstall, B., V. A. LaBarbera, N. M. Brunet, B. J. Gavino, L. Herring, S. Heshmati, B. H. Kraft, V. Inchausti, N. L. Meyer, D. Moonoo, A. K. Takeda, and P. B. Chase. Interaction between troponin and myosin enhances contractile activity of myosin in cardiac muscle. DNA Cell Biol. 30:653–659, 2011.CrossRefGoogle Scholar
- 58.Wang, F., N. M. Brunet, J. R. Grubich, E. Bienkiewicz, T. M. Asbury, L. A. Compton, G. Mihajlović, V. F. Miller, and P. B. Chase. Facilitated cross-bridge interactions with thin filaments by familial hypertrophic cardiomyopathy mutations in α-tropomyosin. J. Biomed. Biotechnol. 2011:435271, 2011.Google Scholar
- 61.Weast, R. C. (ed.). CRC Handbook of Chemistry and Physics. Boca Raton, FL: CRC Press, 1982.Google Scholar