Enhanced force generation by smooth muscle myosin in vitro.
To determine whether the apparent enhanced force-generating capabilities of smooth muscle relative to skeletal muscle are inherent to the myosin cross-bridge, the isometric steady-state force produced by myosin in the in vitro motility assay was measured. In this assay, myosin adhered to a glass surface pulls on an actin filament that is attached to an ultracompliant (50-200 nm/pN) glass microneedle. The number of myosin cross-bridge heads able to interact with a length of actin filament was estimated by measuring the density of biochemically active myosin adhered to the surface; with this estimate, the average force per cross-bridge head of smooth and skeletal muscle myosins is 0.6 pN and 0.2 pN, respectively. Surprisingly, smooth muscle myosin generates approximately three times greater average force per cross-bridge head than does skeletal muscle myosin.
VanBuren
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Department of Cardiology, University of Vermont, Burlington 05405.
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D000199:Actins / Q000502:physiology; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002645:Chickens; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000502:physiology*; D009218:Myosins / Q000502:physiology*; D014422:Turkeys
D000199:Actins; D009218:Myosins