The R133W beta-tropomyosin mutation was associated with lower specific force (P<0.05) and rate constant of force redevelopment (P<0.01), and faster maximum velocity of unloaded shortening (P<0.05).
Case-Control
Does the R133W beta-tropomyosin mutation alter the regulation of muscle contraction in single human muscle fibres?
The R133W beta-tropomyosin mutation alters myosin-actin kinetics, causing a reduced number of myosin molecules in the strong actin-binding state and resulting in muscle weakness.
p-value: p=<0.05
A novel R133W beta-tropomyosin (beta-Tm) mutation, associated with muscle weakness and distal limb deformities, has recently been identified in a woman and her daughter. The muscle weakness was not accompanied by progressive muscle wasting or histopathological abnormalities in tibialis anterior muscle biopsy specimens. The aim of the present study was to explore the mechanisms underlying the impaired muscle function in patients with the beta-Tm mutation. Maximum force normalized to fibre cross-sectional area (specific force, SF), maximum velocity of unloaded shortening (V0), apparent rate constant of force redevelopment (ktr) and force-pCa relationship were evaluated in single chemically skinned muscle fibres from the two patients carrying the beta-Tm mutation and from healthy control subjects. Significant differences in regulation of muscle contraction were observed in the type I fibres: a lower SF (P<0.05) and ktr (P<0.01), and a faster V0 (P<0.05). The force-pCa relationship did not differ between patient and control fibres, indicating an unaltered Ca2+ activation of contractile proteins. Collectively, these results indicate a slower cross-bridge attachment rate and a faster detachment rate caused by the R133W beta-Tm mutation. It is suggested that the R133W beta-Tm mutation induces alteration in myosin-actin kinetics causing a reduced number of myosin molecules in the strong actin-binding state, resulting in overall muscle weakness in the absence of muscle wasting.
Ochala et al. (Fri,) conducted a case-control in R133W β-tropomyosin mutation with muscle weakness. R133W beta-tropomyosin mutation vs. Healthy control subjects was evaluated on Specific force (SF), maximum velocity of unloaded shortening (V0), and apparent rate constant of force redevelopment (ktr) in type I fibres (p=<0.05). The R133W beta-tropomyosin mutation was associated with lower specific force (P<0.05) and rate constant of force redevelopment (P<0.01), and faster maximum velocity of unloaded shortening (P<0.05).