Thick filament structural changes in the presence of calcium. (A) The intensity of the third-order of myosin-based meridional reflection (I_M3) from permeabilized porcine myocardium under resting (pCa 8.0) and activated (pCa 4.5) state from WT and D65A. (B) The first-order myosin-based layer line (I_MLL1) from permeabilized porcine myocardium under resting (pCa 8.0) and activated (pCa 4.5) state from WT and D65A. (C and D) The spacing of the third (C) and sixth-order (D) myosin-based meridional reflections (S_M3 and S_M6, respectively) from permeabilized porcine myocardium under resting (pCa 8.0) and activated (pCa 4.5) state from WT and D65A.