Slip sliding away: load-dependence of velocity generated by skeletal muscle myosin molecules in the laser trap - PubMed (original) (raw)

Slip sliding away: load-dependence of velocity generated by skeletal muscle myosin molecules in the laser trap

Edward P Debold et al. Biophys J. 2005 Nov.

Abstract

Skeletal muscle's ability to shorten and lengthen against a load is a fundamental property, presumably reflecting the inherent load-dependence of the myosin molecular motor. Here we report the velocity of a single actin filament translocated by a mini-ensemble of skeletal myosin approximately 8 heads under constant loads up to 15 pN in a laser trap assay. Actin filament velocity decreased with increasing load hyberbolically, with unloaded velocity and stall force differing by a factor of 2 with [ATP] (30 vs. 100 muM). Analysis of actin filament movement revealed that forward motion was punctuated with rapid backward 60-nm slips, with the slip frequency increasing with resistive load. At stall force, myosin-generated forward movement was balanced by backward slips, whereas at loads greater than stall, myosin could no longer sustain forward motion, resulting in negative velocities as in eccentric contractions of whole muscle. Thus, the force-velocity relationship of muscle reflects both the inherent load-dependence of the actomyosin interaction and the balance between forward and reverse motion observed at the molecular level.

PubMed Disclaimer

Figures

FIGURE 1

FIGURE 1

(A) F/V data at 30 _μ_M (red circles) and 100 _μ_M ATP (black triangles) as means ± SE. Hill F/V fit to positive loads only (lines; see text) at 30 _μ_M ATP (_F_o = 15 pN, a/_F_o = 0.29, b = 0.21 _μ_m/s) and 100 _μ_M ATP (_F_o = 6 pN, a/_F_o = 0.33, b = 0.53 _μ_m/s). (B) Only increasing load sequence shown with force levels above displacement trace. (C) Filtered actin displacement traces (at 100 _μ_M ATP) at different loads with their respective linear regressions used to determine actin filament velocity; 10–90 velocities at each load were averaged to generate F/V in panel A.

FIGURE 2

FIGURE 2

Characterization of slips at 100 _μ_M ATP (similar results obtained at 30 _μ_M ATP). (A) Slip frequency versus load (r = 0.84). Inset is a displacement record with a rapid reversal or “slip” in response to 5 pN. (B) Slip amplitude versus force, each point is the mean ± SE. Regression omits 1-pN data yielding 60-nm average amplitude. (C) F/V data with (▪, solid line) and without slips (○, dashed line) and fit with Hill F/V equation.

Similar articles

Cited by

References

    1. Hill, A. V. 1938. The heat of shortening and the dynamic constants of muscle. Proc. R. Soc. Lond. B. Biol. Sci. 126:136–195.
    1. Huxley, A. F. 1957. Muscle structure and theories of contraction. Prog. Biophys. Biophys. Chem. 7:255–318. - PubMed
    1. Harris, D. E., and D. M. Warshaw. 1993. Smooth and skeletal muscle myosin both exhibit low duty cycles in vitro. J. Biol. Chem. 268:14764–14768. - PubMed
    1. Visscher, K., M. J. Schnitzer, and S. M. Block. 1999. Single kinesin molecules studied with a molecular force clamp. Nature. 400:184–189. - PubMed
    1. Kad, N. M., A. S. Rovner, P. M. Fagnant, P. B. Joel, G. G. Kennedy, J. B. Patlak, D. M. Warshaw, and K. M. Trybus. 2003. A mutant heterodimeric myosin with one inactive head generates maximal displacement. J. Cell Biol. 162:481–488. - PMC - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources