]>Tropomyosin Period 3 Is Essential for Enhancement of Isometric Tension in Thin Filament-Reconstituted Bovine Myocardium : Figure 2
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Figure 2: Slow pen trace of isometric tension in the standard activating solution (pCa 4.66, 5 mM MgATP, 8 mM Pi, ionic strength 200 mM, 15 mM CP, 320 units/ml CK, pH 7.00) at different temperatures (indicated). Experiments were performed in thin filament-reconstituted cardiac muscle fibers, in which nfTm (A), ▵ 2 T m (B), and ▵ 3 T m (C) were added back, together with bovine cardiac Tn. D, activation of native fibers; E, activation of thin filament-extracted fibers after gelsolin treatment for 50–90 minutes; F, activation of actin filament-reconstituted fibers; and G, activation of Tm- and Tn-reconstituted fibers. H, activation at eight different temperatures, as indicated. Between D, E, F, and G, the pen recorder was stopped so that extraction and reconstitution could be performed (at 0 ∘ C ). Before each activation, the muscle fibers were washed in the standard activating solution (at 0 ∘ C ), which did not induce tension. Tension was induced by switching the fibers to a bath of the same solution at the higher temperature. The fibers were relaxed in the Rx solution that contained 40 mM BDM at 0 ∘ C . Horizontal bars below the pen trace in C indicate that the temperature was 0 ∘ C during relaxation. The active tension in F develops as the result of withdrawal of BDM, and the temperature rises to 2 5 ∘ C . The active tension is relaxed as the result of the addition of 40 mM BDM, and the temperature drops to 0 ∘ C . Calibrations are 1 min (abscissa) and 10 kPa (ordinate).