Force-generating capacity of human myosin isoforms extracted from single muscle fibre segments.
Muscle, motor unit and muscle fibre type-specific differences in force-generating capacity have been investigated for many years, but there is still no consensus regarding specific differences between slow- and fast-twitch muscles, motor units or muscle fibres. This is probably related to a number of different confounding factors disguising the function of the molecular motor protein myosin. We have therefore studied the force-generating capacity of specific myosin isoforms or combination of isoforms extracted from short single human muscle fibre segments in a modified single fibre myosin in vitro motility assay, in which an internal load (actin-binding protein) was added in different concentrations to evaluate the force-generating capacity. The force indices were the x-axis intercept and the slope of the relationship between the fraction of moving filaments and the α-actinin concentration. The force-generating capacity of the β/slow myosin isoform (type I) was weaker (P < 0.05) than the fast myosin isoform (type II), but the force-generating capacity of the different human fast myosin isoforms types IIa and IIx or a combination of both (IIax) were indistinguishable. A single fibre in vitro motility assay for both speed and force of specific myosin isoforms is described and used to measure the difference in force-generating capacity between fast and slow human myosin isoforms. The assay is proposed as a useful tool for clinical studies on the effects on muscle function of specific mutations or post-translational modifications of myosin.
Li
Meishan
M
Department of Clinical Neurophysiology, Uppsala University Hospital, SE-751 85 Uppsala, Sweden.
Larsson
Lars
L
D000185:Actinin / Q000494:pharmacology; D000328:Adult; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009218:Myosins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms
D020033:Protein Isoforms; D000185:Actinin; D009218:Myosins