Figure 5.

Influence of motility conditions on temperature dependence of filament sliding speeds for (a) unregulated F-actin and (b) regulated thin filaments (F-actin plus native cTn and α-Tm) at pCa 5. Points are the mean of means ± S.D. from 45–75 filaments in each of ≥3 individual flow cells and are plotted against steady-state temperature (27– 42°C) for four conditions. For this series of experiments only, control conditions (circles, solid lines) were [Pi] = ∼1 μM (achieved by removal of contaminating Pi; Section 2); [ATP] = 2 mM (buffered by CP and CK; Section 2), and high ρ achieved by infusing 0.25 mg/mL [HMM] into the flow cell. Conditions were modified to test low ATP (200 μM ATP; inverted triangles, short dashed lines); high Pi (4 mM Pi; squares, long dash dotted lines); or low ρ (0.075 mg/mL HMM; triangles, dash dotted line). Lines were drawn to connect the points. Insets: temperature dependence of fraction of filaments moving under low ρ condition plotted for (a) unregulated F-actin and (b) regulated thin filaments at pCa 5. Note that the fraction of regulated thin filaments, but not unregulated F-actin, increases continuously over this temperature range.