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. Author manuscript; available in PMC: 2015 Jun 15.

Published in final edited form as: Arch Biochem Biophys. 2013 Nov 20;0:83–91. doi: 10.1016/j.abb.2013.11.005

A & B. Theoretical model of thin filament compliance (e.g., tropomyosin persistence length) with sarcomere length and longer titin isoforms. Faster force development at short SL (bar plots in A) may arise from greater thin filament compliance and less cooperative recruitment of force-generating cross-bridges. According to this idea force development rates (indexed by k_tr) should be greater in myocytes with longer more-compliant N2BA titin (theoretical bar plots in panels A & B). C–E. While k_tr during maximal Ca²⁺ activation was not different between N2B and N2BA myocytes at sarcomere length 2.30 μm (C & D), k_tr was faster in N2BA myocytes during submaximal Ca²⁺ activations (C & E). This difference is more evident when assessed by the k_tr ratio between half-maximal Ca²⁺ activated force (0.5 pCa 4.5) and maximal Ca²⁺ activation (pCa 4.5) (E). Bar plots are means ± SEM; *p<0.05, n = 7 for each group.

A & B. Theoretical model of thin filament compliance (e.g., tropomyosin persistence length) with sarcomere length and longer titin isoforms. Faster force development at short SL (bar plots in A) may arise from greater thin filament compliance and less cooperative recruitment of force-generating cross-bridges. According to this idea force development rates (indexed by k_tr) should be greater in myocytes with longer more-compliant N2BA titin (theoretical bar plots in panels A & B). C–E. While k_tr during maximal Ca²⁺ activation was not different between N2B and N2BA myocytes at sarcomere length 2.30 μm (C & D), k_tr was faster in N2BA myocytes during submaximal Ca²⁺ activations (C & E). This difference is more evident when assessed by the k_tr ratio between half-maximal Ca²⁺ activated force (0.5 pCa 4.5) and maximal Ca²⁺ activation (pCa 4.5) (E). Bar plots are means ± SEM; *p<0.05, n = 7 for each group.