Figure 3. Mechanical properties of skeletal muscle are regulated by detyrosinated MT filaments.

(a) Sarcomere shortening was assayed in single FDB fibres contracting with single action potential stimulation (1 Hz; field stimulation) under no-load conditions (see Methods). Representative raw SL measures of control (black) and PTL (red) treated fibres are shown. Neither taxol nor PTL treatment significantly altered resting SL or the per cent change (% change) in SL compared with the control condition. (b) PTL significantly increased the maximal velocity of contraction, although relaxation kinetics were unaltered. Taxol treatment did not significantly alter either contraction or relaxation velocity. However, PTL significantly decreased, while taxol significantly increased, the time to peak SL shortening. *P<0.05 (n=10 control, 18 PTL, 14 taxol). Statistical significance determined by using a Kruskal–Wallis with Dunn's post hoc test. (c) Following PTL treatment, Ca²⁺ transients (displayed as the resulting ratio, F(a.u.)) were assayed using the ratiometric dye, Indo1-PE during unloaded shortening of single FDB fibres (n=5 cells per treatment). PTL did not affect peak calcium or the kinetics of rise or decay. Statistical significance determined by Student's t-test. All values are mean±s.e.m.