Crossbridge kinetics in chemically skinned rabbit psoas fibres when the actin-myosin lattice spacing is altered by dextran T-500.
The actin-myosin lattice spacing of chemically skinned rabbit psoas fibres was osmotically altered by dextran T500, and the transient kinetic response of tension arising from maximally cycling cross-bridges was measured by sinusoidal length perturbations. The lattice spacing was estimated from the width of the fibres measured under a light microscope. As the dextran concentration was increased, the widths during both relaxation and Ca-activation decreased monotonically. The tension increased to a maximum at 7% dextran, and decreased again at further increases in dextran. Dynamic modulus (stiffness) increased monotonically with compression by dextran; this increase is primarily due to the elastic modulus. The rate constants slightly decreased between 0% and 4% dextran, then decreased rapidly at higher concentrations. The rate of oscillatory work output stayed approximately constant between 0% and 4% dextran, and sharply decreased at higher concentrations. Apparently, two independent effects occur as the lattice is compressed by dextran: (1) a compensation for the spacing change through an increase in tension and a decrease in the rate constants (this takes place at low dextran concentrations); and (2) an alteration of the crossbridge kinetics by grossly decreasing both the tension and the rate constants (at high dextran concentrations). The first effect is interpreted as a decrease in the detachment rate, while the second effect is interpreted as a decrease in the rate of the 'power stroke' reaction.
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D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003911:Dextrans / Q000494:pharmacology*; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects*; D009127:Muscle Rigidity / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D009994:Osmolar Concentration; D011817:Rabbits; D014783:Viscosity
D000199:Actins; D003911:Dextrans; D000255:Adenosine Triphosphate; D009218:Myosins